# How do I model a supercharger rotor?



## aonemarine

Tring to figure out how to model the hypocycloidal and epicycloidal curves of a supercharger rotor in alibre cad.  This is really making me pull my hair out!
  Steve H, have you managed this with your model blower??
Im trying to design a 3 lobe rotor for a  blower with a 71ish cid displacement...


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## GailInNM

Several different ways. 
Here are the basic equations.

Roots blower impeller is combination of Hypocycloid and Epicycloid curves
switching from one to the other whenever they touch.

a is equal to large circle radius and b equal to small circle radius
Origin is center of large circle. t is the radial angle.
 These are for 2 loves.  I have the equations for other lobe patterns but not handy right now.
Gearotic will also generate them for CAD input.

Hypocycloid
x = (a - b) cos(t) + b cos((a/b - 1)t), y = (a - b) sin(t) - b sin((a/b - 1)t) 

Epicycloid
x = (a + b) cos(t) - b cos((a/b + 1)t), y = (a + b) sin(t) - b sin((a/b + 1)t) 

If your modeling program can take parametric inputs then you are home free.  If not, dump the equations into a spread sheet and import it something like this and then smooth it.  You can set "t" to as fine a resolution as you want.

I can help you set any of it up if you need help.
Gail in NM



		Code:
	

pline
1.0000,0.0000
0.9886,0.0007
0.9551,0.0052
0.9012,0.0173
0.8298,0.0400
0.7444,0.0755
0.6495,0.1250
0.5497,0.1887
0.4495,0.2656
..........


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## aonemarine

Thanks for the input Gail.   I think i might be able to bumble through the equation for the 2 lobe rotors,  but what about for a 3 lobe rotor?  Im no engineer,  so this is going to take me some to sort out and understand so forgive the stupid question.  The equation is for basically plotting points to create the hypo/epicycloidal arcs and (t) would be the resolution?   Ugggg....wish i would have paid more attention in school....

Edit:  t= radial angle,  i should have read your example more closely...


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## aonemarine

Ok, i think im really screwing this up. Someone check me on this please. On the hypocycloid, A=3  B=2 T=1 i get X=2.9997715414???   Is that right?  If it is, what do i need to do to get the next position???
Uggg. My brain aches now....


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## barnesrickw

Just out of curiosity, does this require a four or five axis cnc?


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## aonemarine

barnesrickw said:


> Just out of curiosity, does this require a four or five axis cnc?



You could do it on a manual 3 axis mill with a rotary table or dividing head. Once you figure out the math anyway....


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## GailInNM

When I first posted I was on my way out the door and just got back in and have some time to expand a little bit on what I said. A little bit will depend on what tools you have available, both computer and machine tools.

Do you have Excel?  If so I will update a spread sheet that I wrote a long time ago to do all the calculations for you.  When I wrote it, it was just for my own use so I did not put any notes in it or make it easy to change parameters.  Won't take but a little while to clean it up. 
Gail in NM


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## johnmcc69

Do you have a pic or sketch with some rough dim's you could post?

John


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## aonemarine

Yes, i do have excel.  Was my math atleast correct?  I enjoy figuring things out in traditional manners, it makes things more clear over the long run.


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## aonemarine

johnmcc69 said:


> Do you have a pic or sketch with some rough dim's you could post?
> 
> John



Not yet. I had done some modeling of some rotors before, but the geometry was not correct and any lash in the gears would cause the rotors to collide.  The rotors were 3" dia 3 lobe and the lobe ends were .5" radius.  With a 10" long rotor the displacement would have been aprox 72 ci.  I 3d printed the rotors with the intention of investment casting them. I never cast them.
I can post a pic of them if you would like.?


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## GailInNM

I think you are off.  The original equations I gave you have a couple of conditions and I should have mentioned them.  My poor memory ne3eded a refresh.  

The ratio between the circles must be an integer relationship.  That is the large circle divided by the small circle must equal 2,3,4...etc. This ratio determines  the number of lobes.  Give me about 1/2 an hour and I will update the Excel spread sheet and that will make it easy for you to check your math.

Second item is that the angle in the original equations is in radians so if you are working in degrees they will have to be converted to radians.  That is 2Pi radians = 360 degrees.  The spread sheet will do the conversions.

Gail in NM


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## aonemarine

well that explains a couple of things. I should have set a=4 and b=1, also explains why t=180 or t=360 both had x=-1 LOL
this was a small test model,



and here were the printed rotors,




sooner or later ill get it sorted out LOL


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## rcfreak177

I did this some time ago on BobCad.
Was quite a lengthy task. I did make the rotors on a 4 axis machine, they came out well but have since melted them down for another project. There were 7hrs machining Time in each rotor from 75mm dia billet 7075. Next time I will be casting them allowing for finish machining in order to cut down the operation time. 

I have played with Alibre but am not very good with it.


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## GailInNM

Sorry for the delay.  I had some power hits that slowed me down.
I have attached the Excel spread sheet.  You can play with it to double check your numbers.

I will post a few screen shots of what it looks like imported into Autocad tomorrow evening.  Busy day tomorrow during the day.

You can change the number of increments, number of lobes and the large circle radius.  The small circle radius is calculated from the large circle radius and number of lobes.

Sheet is set up for a sample with 5 degree increments which is too coarse for machining but it gives you the idea.

Gail in NM 

View attachment Roots2.xls


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## barnesrickw

I have seen roots type blowers that have "straight rotors". They move air from top to bottom at low pressure.


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## MachinableWax

Not sure if this helps any, but this is a helpful link for M62, and M90 Eaton superchargers.  It has some dimensions, and twist angles. http://www.3800supercharger.net/

I can's seem to find it, but I know the guy who made that site has also made a cad animation of the basic function of the M62.  Not sure if he has an detailed cad on the rotors though.  Might be worth sending him an email from the contact info on that site.  His name is Bill.  

Also, if it would help, I have a couple of each version if you want any dimensions from them.   Actually, I have a set of M62 rotors I do not need.  You can have them if you pay for shipping.


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## aonemarine

The eatons are an entirely different beast than the roots type superchargers. I really need to stay with the roots type for simplicity. I plan on making a pair of these supechargers for the flathead im building for betsy. Im not sure that twin superchargers of such reduced size is a wise idea, but it would look cool


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## MachinableWax

If you change your mind, the offer is still on the table.


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## aonemarine

I thought they were screw type compressors??  Maybe i need to take a better look at them.


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## GailInNM

Aone: I know that you are beyond this point but since there are quite a few people following this thread I wanted to post a little bit of one way to get from the equations to a drawing of a roots blower rotor or coordinates that can manipulated for machining. 

To get to a drawing in Autocad I extract the X and Y coordinate columns for both the hypocycloidal and epicycloidal into two comma delimited files that I can use for script files to generate a polyline for each. The polylines are overlaid on each other and then used to trim each other wherever they cross.

The photo show first the hypocycloidal and then the epicycloidal curves as plotted from the above spreadsheet. Then they are overlaid on each other and trimming begins with the last photo showing the result rotor outline.
Gail in NM


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## aonemarine

Gail, you give me too much credit.... Im still learning, just like many following this thread  Thank you for your time helping us out.


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## MachinableWax

aonemarine said:


> I thought they were screw type compressors??  Maybe i need to take a better look at them.



I have heard them referred as roots blowers over the years, but I looked it up, and this is wrong.  They are twin screw.  My mistake.


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## aonemarine

MachinableWax said:


> I have heard them referred as roots blowers over the years, but I looked it up, and this is wrong.  They are twin screw.  My mistake.



Im still trying to figure that one out, they are high helix rotors designed to pull air from the back of the case and push the air forward a bit before dumping it out the bottom, but there are also 8-71 blowers that are 3 lobe high helix rotors that are draw thru type. Question is would the eaton rotors work as a draw thru supercharger if the case was altered? Ive been trying to look up the twist on the 8-71 high helix rotors but havent found it yet....still searching...


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## aonemarine

NEW ENFORCER SUPERCHARGERS 
The NEW E-Force Enforcer Supercharger systems for small-block & LS Chevy are a traditional positive displacement supercharger that is ideal for use in street rod and muscle car applications. They include a newly designed intake assembly with Eaton Gen VI 2300 TVS internals, manifold, drive pulleys, 10-rib serpentine belt, and all the necessary hardware. Complete systems are pre-assembled for an easy bolt-on installation. E-Force supercharger systems are available with or without dual-carburetors and EFI throttle bodies. These systems are designed to be installed on a factory style front end drive. Will not work directly with aftermarket serpentine systems. Both systems are available in a natural satin aluminum or high quality polished finish for a show quality classic look. Compatible with 6-7/16" center-to-center air cleaners

Maybe?? I would love to see a breakdown of the case to make sure they arent doing anything strange with the flow path...


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## aonemarine

this pretty much sums it up, the air is redirected from the carb to the back of the housing.....
http://www.hotrod.com/how-to/engine/hrdp-0903-small-block-chevy-blower/#photo-02


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## MachinableWax

When you say back of the housing, do you mean the area of the s/c housing that is closest to the distributor when mounted?  

I would think that the air flow would go straight down, and into the LIM.


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## aonemarine

Pulley side = front. 
Basically, they made a custom case but kept the admission point at the rotors the same as the eaton.
You can really see it in the link i posted above.


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## MachinableWax

If you look at pictures 6, 8, and 9 in the gallery of this link http://www.superchevy.com/how-to/0610ch-magnuson-superchargers/parts-cost.html it looks like the only function of the back side of the housing is for the boost bypass valve.  It looks to me that the air flow goes straight down, from what I can see in those pics.


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## stevehuckss396

aonemarine said:


> Tring to figure out how to model the hypocycloidal and epicycloidal curves of a supercharger rotor in alibre cad.  This is really making me pull my hair out!
> Steve H, have you managed this with your model blower??
> Im trying to design a 3 lobe rotor for a  blower with a 71ish cid displacement...



I seem to be a little late to the party. I didn't use any fancy math, just trial and error. The radii on the lobes needs to be smaller than the radii in the valleys. The difference in radii depends on the clearance you want. I made by rotors with a .005 clearance so the outside diameter was .010 smaller than the bore and the radius on the nose was .005 smaller than the radius in the valley. The perfect fit is so no rotating parts touch so the pair get installed and geared together. Then they get blued and checked for wear spots. Alot of hand work to get them tight but not touching.

I basically took two bores on a known center (for gear mesh) and designed a rotor to fit. Sorry I cant help more than that.


Machining the lobes
[ame]https://www.youtube.com/watch?v=wF3fiEoAVKA[/ame]


Machining the valleys
[ame]https://www.youtube.com/watch?v=jhOgIGKxnC0[/ame]


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## aonemarine

MachinableWax said:


> If you look at pictures 6, 8, and 9 in the gallery of this link http://www.superchevy.com/how-to/0610ch-magnuson-superchargers/parts-cost.html it looks like the only function of the back side of the housing is for the boost bypass valve.  It looks to me that the air flow goes straight down, from what I can see in those pics.



  From thier description of the housing...

Inside the housing, the air travels from the carburetor to the rear of the housing, then into the inner cleaves of the rotors and out the bottom; this is described as an axial flow.

  I think it may be possible to cast a housing that will work (they did).  Ill be putting more thought into canabilizing one of the eatons. i can pick one up off e bay for $150.00 shipped. but right now I have a yoda to attend too


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## MachineTom

Beautiful work on the rotors. Having been inside the blowers of Detroit Diesel engines. The 53 series used a 2 lobe design and the 71 series used a 3 lobe helix design. Both rotors had 3 lands at the top of the lobe, similar to the way a drill is relieved at the lands.these had a close clearance of about .003"to the matching root. if I recall, When fitted to automotive engines blowers had the lands replaced with teflon strips, so to run near zero clearance. 

I had an Eaton blower on my Honda motorcycle, That was a two lobe design. That was a Beast.


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## ajk5292963

i need super charger profile,can some body help me out?


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## johnmcc69

Do you have a pic or sketch of what you have in mind?


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## mattb.351

aonemarine said:


> Ive been trying to look up the twist on the 8-71 high helix rotors but havent found it yet....still searching...



This site reckons the angle for a 6-71 is 30 degrees. I guess the 8-71 would be similar.

http://victorylibrary.com/mopar/blower/blower-GMC2.htm

I guess the limiting factor on the upper helix angle would be that that the back edge of the rotor has sealed against the housing before the front edge opens into the plenum. As you are probably aware, they did the twist to lessen the pulsing effect that supposedly happens with the straight rotors.

How would you machine the helix on a manual mill? Or will you be doing straight rotors? You could design the housing to allow the trailing edge (near the back) of the rotor to be closed last and the leading edge of the rotor to be opened first (triangular shaped opening) if pulsing was an issue. I suppose there'd be some tradeoff for volume pumped, but you could just design it a little larger to compensate.


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## Badhippie

Maybe this is something I can help you with I have personally rebuilt hundreds of blowers in my time and btw Machine Tom is correct in his statements. I would think this is where a rotary table would maybe help. But if you think about it wouldn’t you be better off by casting the part first then machining it from a casting. Since you are wanting to do this without A CNC. Also instead of using the old style 2 or 3 lobe rotors. Would it be easier to machine twin screws they are way more efficient then the old style 2 or 3 lobe design in every aspect. If you are wanting the rate of twist for the lobes I probably have that information written down somewhere in my notes. 
Just throwing in my opinion which won’t even buy you a cup of coffee


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## propclock

Just my thoughts. My friend Dwight Giles has a 1/3 scale blown v8
Black Widow. It started to smoke and he allowed me to overhaul it.
On rebuild all internals were perfect , some small scoring on the cylinders. I thought just no air cleaner and many years of running at shows. But a close look at the blower lobes shows they were making
occasional contact, and guess where that aluminum/
 aluminum oxide  goes. So the gears have to be perfect the machining has to be perfect  and then no problem. Otherwise !!!
and another note seal the main shaft, Dwight's had a vacuum leak
and prevented a low idol I used a sealed bearing backed up with a Teflon home made seal.  
I think rotors made out of Delrin would be a better choice.
Untested & untried but ??? Whos 2 know. 
Just my 1.414 cents worth


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## stevehuckss396

Just my 1.414 cents worth



45 degrees!


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## Bentwings

stevehuckss396 said:


> Just my 1.414 cents worth
> 
> 
> 
> 45 degrees!


After a lot of searching I found the Spirograph kit or toy. I’ve ordered it just to help me understand how the process works. 
I have a complete 6-71 in excellent near new condition so I have something to look at and take measurements from.  It’s been a long time since I built my first racing blower. I did my Willys  streetrod one and drove it some 30k miles just weekly cruising back roads.
I really appreciate your work on this project. I’m sure I’ll have more questions.  I’d like to create a printed working plastic model then maybe a metal printed one.  I’ll have to investigate costs as I don’t have either process myself.  There are places near me that I can work with however. 
a gentleman made a screw blower YouTube series however it failed to produce boost.  He said tolerances are just too close for his shop.  I know even the race guys spend incredible amounts for these superchargers.  I ran 6-71 and 8-71 for a long time on our funnycars.  These had nylatron seal strips that had to be replaced regularly.  It was a fun era of my life.
byron


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## mrehmus

I think the Gearotic software will model one for you.


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## lohring

I think liquid seal compressors are often overlooked as superchargers for small engines.  They are easy to build and can use fuel as the seal.  They have built in intercooling and metering the fuel input should work.  See Liquid Ring Compressors | Products & Systems | Nash

Lohring Miller


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## lohring

Take a look at this video to get an idea of how to build one..  

Lohring Miller


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## awake

lohring said:


> Take a look at this video to get an idea of how to build one..
> 
> Lohring Miller



That was helpful - I was not understanding how this would work until I saw this animation. The key seems to be that some of the liquid seal is extracted with the gas, and must be replenished - is that correct?


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## lohring

Yes, and if the seal is fuel, you have a well mixed air/fuel mixture fed into the engine intake.

Lohring Miller


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## awake

lohring said:


> Yes, and if the seal is fuel, you have a well mixed air/fuel mixture fed into the engine intake.
> 
> Lohring Miller


That is cool ... except, how do you control the amount of fuel going into the mixture? Is it a function of how much fuel is fed into the liquid input?


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## mattb.351

propclock said:


> Just my thoughts. My friend Dwight Giles has a 1/3 scale blown v8
> Black Widow. It started to smoke and he allowed me to overhaul it.
> On rebuild all internals were perfect , some small scoring on the cylinders. I thought just no air cleaner and many years of running at shows. But a close look at the blower lobes shows they were making
> occasional contact, and guess where that aluminum/
> aluminum oxide  goes. So the gears have to be perfect the machining has to be perfect  and then no problem. Otherwise !!!
> and another note seal the main shaft, Dwight's had a vacuum leak
> and prevented a low idol I used a sealed bearing backed up with a Teflon home made seal.
> I think rotors made out of Delrin would be a better choice.
> Untested & untried but ??? Whos 2 know.
> Just my 1.414 cents worth


Would a thorough running in on the bench (just the blower) help in this regard? Even going as far as heating the assembly up to engine running temperature. What's the clearance on a full size blower meant to be? Say a 6-71?


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## Bentwings

mattb.351 said:


> Would a thorough running in on the bench (just the blower) help in this regard? Even going as far as heating the assembly up to engine running temperature. What's the clearance on a full size blower meant to be? Say a 6-71?


We often took either a new blower or a rest ripped one out of the box and bolted it on the racer. At best it got a warm up of a few minutes then it was run flat out. The big hemi would run 8500 rpm snd that was it. It was valve spring limited even with titanium valves and moving valve train parts. Valve springs lasted 4-4 runs at best. So we were. Instantly ordering them and replacing them. We ran the blower at 50% over drive. It wasn’t well known then that the blowers were good for about 8500 blower rpm . We sacrificed top end speed for the power boost of the line line.  High gear was like ho him, look around and see if the competition was close.  We kept leaning the fuel and adding timing.  Actually probably going down on overdrive might have helped overall but we were going quicker and faster each run by leaning it out and adding timing. There were multi stage lean out valves but we just didn’t get that far. It was important to make a good show and make all your runs match racing. The power of the dollar.in 5 years running we only lost one run due to breakage. We blew up a clutch but the remains stayed locked up enough to make it down the track.  Believe me I had my knees in my face on that one. Through a hurclean effort  and a borrowed clutch we came back and won the event.  Cost wise it was an expensive weekend but the effort got us a return match race that we also won so I suppose it was a wash dollar size.  It’s a great memory we hash over every reunion.  One of those “play hurt” sporting events.
I did watch the video and got a good handle on how these blowers are developed.  I have a set of near new rotors to measure and a perfect case so I’m going to try and model 3dprinted blower. I don’t have s printer but there are lots of shops near me that do.  I’m not sure what scale to model to but it’s easy to change that.  The screw blower video was fun but sad that the unit didn’t work. It apparently made some cool noise. The real racers run them pretty fast but I think the printed model might not survive.

byron


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## lohring

awake said:


> That is cool ... except, how do you control the amount of fuel going into the mixture? Is it a function of how much fuel is fed into the liquid input?


Model engines use a needle valve.  You may need to get fancier if anything other than full throttle operation is needed.

Lohring Miller


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## mu38&Bg#

As a cheap, low tech pump, if it made sense in engines I think there would be at least a few examples in history. Sealing liquid entrainment and poor efficiency is probably why they aren't used.


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## Bentwings

dieselpilot said:


> As a cheap, low tech pump, if it made sense in engines I think there would be at least a few examples in history. Sealing liquid entrainment and poor efficiency is probably why they aren't used.


The mechanical fuel injection used in top fuel and alcohol racers is far from simple or cheap. Even back in the old days. The fuel pumps are very high pressure and very precise items. Carefully flow tested and mapped. Even nozzle check valves and distribution blocks are tested and log books are kept. The. Percentage of fuel that goes into the blower is noted and manifold temp pressure and weather data enter into the picture. Rules prevent computerization but allow viewing after each run. In the old days we only had spark plugs to monitor the burn conditions. They were replaced after each run so en back then a notable expense. You always talked nice to the suppliers and ran their stickers if you had their sponsorship. They were about $ 5:00 bucks apiece then, much more now. So 24-36 a day counted up. They couldn’t be used in your daily driver or truck either.  There was quite a trick to reading spark plugs depending on fuel used and motor tune up. Everything did something to how hot the plug got and what it looked like after a run. We didn’t have nice cameras like today if you took any with your 35mm camera it would be a week before you got them back. Sometimes I wonder how we ever got down the track. It was a bad run if you didn’t burn or wreck at least one piston a run. 1-200 bucks each depending on if you could save them . I cut new grooves in lots of them.  Race stories are always fun when bench racing in the shop.

byron


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## lohring

There were two supercharged four strokes introduced around 1990 for acrobatic RC airplanes.  The first was the YS 120 that used the crankcase as a supercharger.  The second was the OS 120 with a roots supercharger.  Both used pressurized fuel systems with a metering diaphragm.  The YS system prevailed but both are far more complex and heavy than the two stroke OS 60 Hanno Prettner Special they replaced.  

The pressure fuel systems all these engines used could be used to regulate fuel flow into another style supercharger.

Lohring Miller


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## Bentwings

lohring said:


> There were two supercharged four strokes introduced around 1990 for acrobatic RC airplanes.  The first was the YS 120 that used the crankcase as a supercharger.  The second was the OS 120 with a roots supercharger.  Both used pressurized fuel systems with a metering diaphragm.  The YS system prevailed but both are far more complex and heavy than the two stroke OS 60 Hanno Prettner Special they replaced.
> 
> The pressure fuel systems all these engines used could be used to regulate fuel flow into another style supercharger.
> 
> Lohring Miller


I do remember those engines. I don’t think I ever saw a boost pressure posted. Those were not ver big units but very well made. And they did work, probably more as good atomizers than actual pressure. The glow carbs were usually fed from muffler pressure to the fuel tank so fuel dribbled through the needle valve. The velocity of air intake and thrashing in the crankcase provided mixing.  Actually back in early we2 days a draw through carb was used  sustained negative g loads caused engingines to cut out. It was well known on Spitfires.  When the big radials came out with big power something needed to change. I think it was P&W working with Bendix came up with the throttle body fuele injection that ultimately came out on cars with the early efi. These allowed inverted flight and capability I’ve negative g maneuvers. Ed’s entually it was a floatless carb.  Another one of the amazing aero progresses the war brought about. It did take the auto industry 20 years to further developed the concept. I had an original ‘57 chev with the Rochester fuel injection. This unit did have a float system but it remained full controlled by a thing called a spill plunger. This allowed a calibrated fuel flow modulated with an intricate vacuum system. At one point I had a copy of about every tech manual available at the time I also had the adjusting and calibrating equipment that not even dealers had.the car also had an original one of some number nascar related 4 speed transmission. Almost all of these one offs became racers. Mine was raced for several years I was able to equal the nation drag race record but just never could get the exceed percentage at the qualifying races to set the record myself. I never should have sold that car. There a still a few in existence but priceless collector items. There are only a few select parts custom made for them these units were made until 1963 on corvette even those are very rare. It was an exotic car in its day the street versions were often removed and the two four barrel carb systems installed when dealers couldn’t service the fuel injection. These units were stuffed under the bench and forgotten about.
Anyway the glow carb is a very simplified variant of today’s racing mechanical fuel injection. I’ve often wondered if a modern O2 sensor and gage could be made up to help Rc gas engine tuning. The oil in the fuel might make for shorter life for the sensor but I trade a sensor for a well tuned engine any day. I’ve used these on all of my streetrods with great success.

byron


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## Bentwings

mrehmus said:


> I think the Gearotic software will model one for you.


Thanks. I did look this up it apparently had been updated several times. I’ll try and possibly test the free trial version. 
I did order the plastic drawing kit more to help me understand the process . I may end be able to plug in some scaled numbers to get some kind of representation. 
byron


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## lohring

Pipe pressure was used on two strokes.  The above engines used either timed crankcase pressure (YS) or gear pump pressure (OS).  a regulator diaphragm adjusted the flow.  Walbro carbs also use crankcase pressure with a regulator diaphragm.

Lohring Miller


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## Bentwings

lohring said:


> Pipe pressure was used on two strokes.  The above engines used either timed crankcase pressure (YS) or gear pump pressure (OS).  a regulator diaphragm adjusted the flow.  Walbro carbs also use crankcase pressure with a regulator diaphragm.
> 
> Lohring Miller


I used perry pumps and regulators including the vibrating pump on my big twin pattern plane. It was a hungry plane with two 7.5 ducted fan motors. I ran lots of nitro as I was into top fuel drag racing. There was always left over or wrong mix fuel. I just used a hydrometer to sort out what I needed. Glow plugs props fuel were my big expenses.  I flew the plane a lot so it wore itself out constantly. I had spare motors just like we did for the the race car. I could try in through the pattern twice then I had to land for fuel. Mid air refueling would have been cool. We didn’t have the computer radios but today I think it might be possible with FPV and positioning. I found a pet tracker that is radio frequency activated. They flame one foot location. Night mid air refueling?LOL CONSIDERING RADIOS AND THE HOBBY TODAY ID BE IP FOR ABOUT ANYTHING. I was pretty wild in the old days. I’d do anything sports related. It didn’t matter what sport if it was was a game winner gamble Id roll it. Bases loaded 1 run lead score 3-2 count on league heavy hitter and I threw a knuckle ball for a called third strike. Coach made me bat boy for the next three games.


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## Bentwings

Bentwings said:


> I used perry pumps and regulators including the vibrating pump on my big twin pattern plane. It was a hungry plane with two 7.5 ducted fan motors. I ran lots of nitro as I was into top fuel drag racing. There was always left over or wrong mix fuel. I just used a hydrometer to sort out what I needed. Glow plugs props fuel were my big expenses.  I flew the plane a lot so it wore itself out constantly. I had spare motors just like we did for the the race car. I could try in through the pattern twice then I had to land for fuel. Mid air refueling would have been cool. We didn’t have the computer radios but today I think it might be possible with FPV and positioning. I found a pet tracker that is radio frequency activated. They flame one foot location. Night mid air refueling?LOL CONSIDERING RADIOS AND THE HOBBY TODAY ID BE IP FOR ABOUT ANYTHING. I was pretty wild in the old days. I’d do anything sports related. It didn’t matter what sport if it was was a game winner gamble Id roll it. Bases loaded 1 run lead score 3-2 count on league heavy hitter and I threw a knuckle ball for a called third strike. Coach made me bat boy for the next three games.


When you consider that most yard two strokes can operate in about any position, the Walbo and Tilison carbs are pretty good. Our aerobatic planes can fly about any position near constant. They aren’t totally float-less but there is enough crankcase pressure to force fuel through anyway. If you were to come up with a good draw through supercharger they would probably work fine. A blow through might require some fuel tank pressure. I’ve not seen any thing like this but I’d be game to try it if I could.  Someone noted that they had built a centrifugal blower so maybe two staging something like this with with the first stage a draw through on the carb. My question then is you now have a lot of fuel laden air even lightly compressed  it could get dangerous. Most of this would be metal so I wouldn’t expect parts flying all over if there was a back fire.it doesn’t take long before the idea of using a ducted fan as the primary stage but scroll design gets complicated fast. I think a neat small planetary gear drive would be nice here. I may look into this after I get this roots blower out of my head. I haven’t seen much that worked on the Briggs motors but it would be a start. Putting a Walboro carb on the intake of a leaf blower then ducting to the Briggs would be my first choice.those blower housings are often plastic so some static spark could set off a spectacular flash.LOL. My son and grand son are like me try anything once. .


----------



## bdolin

My 1982 Ferrari has Bosch mechanical fuel injection, needa a fuel pump but they are easy to come by.
How about e
An epitracoidal Wankle style engine as a compressor. Relatively easier to machine with oil in the fuel to act as seals


----------



## Bentwings

Today I had opportunity to view the near new condition of a 6-71 blower. It indeed is perfect without a single scratch or mark on the rotors or case. I’ve never seen a new one up close so I’ll be able to get real measurements either in person or by various media. It will be nice to model one from exact measurements for a change. We set up two ways to measure the rotor of one using the lathe readouts the other by assembling the rotors and end plates the measure the diametrical clearance in the case knowing the rotor clearance and the case bore. The case is also without any scratches or scuffing. All that has been done is remove the mounting lip from the side. Standard first step in building a Streetrod or race modified blower. Even the intake and exhaust ribs are in marked and intact. Not sure what we are going to do with it other than preserve it. It would be a collector item at some point so for now it will serve as a measurement source. It’s all clean just a little dusty hopefully I’ll be able to model this exactly then make a high helix model. I may 3D print a scale size for testing as the screw blower guy did. If it works ou I may 3D metal print a scale model too. It would have a better chance of surviving a very high speed test .


----------



## mu38&Bg#

Are you making a scale model of the 6-71? If not a scale model, you may as well start with theory and go from there.


----------



## Bentwings

I’m planning on some scal 1/4 or there about. I’ll have to see about 3D printing cost. We don’t have CBC machining so carving from bilirubin stock is not possible. I know a couple shops near by but material has become so expensive lately that just raw material would be out ic my budget. I can’t print money like the current politicians can.

byron


----------



## Bentwings

lohring said:


> Pipe pressure was used on two strokes.  The above engines used either timed crankcase pressure (YS) or gear pump pressure (OS).  a regulator diaphragm adjusted the flow.  Walbro carbs also use crankcase pressure with a regulator diaphragm.
> 
> Lohring Miller


Hi, I thought I might have described hoe the 6-71 and other gmc blowers work in the real world
So here goes I can get a little long winded when I get into one of my favorite bench racing or shop chats

first the common application is on streetrods. These blower are pretty big so they often stick out of the hood a ways. For street use modified carbs are used. Holley makes special modified ones you can buy o


lohring said:


> Pipe pressure was used on two strokes.  The above engines used either timed crankcase pressure (YS) or gear pump pressure (OS).  a regulator diaphragm adjusted the flow.  Walbro carbs also use crankcase pressure with a regulator diaphragm.
> 
> Lohring Miller


i ws in the middle of a reply and a spam call came in and cut me off so if a reply comes that you don’t understand just delete it. I start over. 6-71 and others like them are pretty big so they stick out of the hood quite a ways. Add carbs and scoop and you get quite an impressive unit. So how does it work? Carbs are normally mounted on top of the blower so they are called draw through. The blower pulls air and fuel through the carb just as normal. At idle the carb acts as normal seeing a vacuum of 15 or more inches. Since only a limited amount can go through there is vacuum in the intake manifold again 15-17 inches. Some will argue this but my cars have had vacuum boost gage on bothe carb and manifold for a long time. When you open the throttle more air/fuel goes in and vacuum drops ubtill you open the throttle far enough then you begin to get boost in the manifold. Now interesting enough there is a huge flow of air through the carb it continues to do it’s job until you exceed its capacity then you begin to see vacuum between the blower and carb. As though the blower isn’t there. You can clearly see this if you have dual vacuum boost gages.I could write a book on what goes on and tuning . I’m not the authority on this but I’ve been very successful puttin 30k miles on my street rods and 200k plus on factory supercharged cars. I. Now tuning. Pulling air and fuel through the car lubricates and cools the blower some. There are inter coolers available that boat guys use these add another’s couple inches to height so not real practical for street use. Blower are great mixture atomizers. You get pretty even mixture in each port and carb calibrated air fuel ratio.I use a gage for this to 0 2 sensor it’s used for accurate tuning adjustment just as modern EFI does. Is just the brain is in my head not an electronic box.
Now lighting the mix is another story . Race cars have used magnetos for many years. Of late there are electronic ignitions that have many features I’ll leave for another day. Roots blower are pretty easy to work with. Now modeling presents another issue. These font scale very well it’s hard to get a small one to pump aid under pressure as you can see in the nice example the gentleman that modeled the screw compressor or blower. Clearances become very critical snd just getting enough air into the unit is hard. This was discovered ver early in the early diesel development. So centrifugal blowers and turbos were developed to force additional air into the gmc blower. This compound supercharging. It could be done in a model but it’s quickly apparent how complicated this could get. Plus you still have machining tolerances to deal with. 
we use a highly developed mechanical fuel injection on the race cars. Grossly simplified its similar to glow fuel model enginges carbs. Basically a barrel valve with a threaded needle valve for fuel control fed with light fuel tank pressure to provide fuel at all time not depending on vacuum assist. In modern race applications ther is a high pressure fuel pump and various pressure/volume control devices. A percentage of fuel is injected above the blower rotors to provide sealing and cooling of the mixture the rest is sprayed into the ports as fine mist the ratios determine power and. Oolong effect.this is well beyond discussion here. Nitro and alcohol do all kinds of things in engines. Sometimes very bad thingsLOL. I’ll try and post a couple pictures of my Streetrod willys. I also have a couple pictures of a friends motor and supercharger ver simulate to mine.
byron


----------



## Bentwings

I know it would be an added expense but there are relatively inexpensive air fuel ratio stand alone gage systems available I had one in several of my supercharged streetrods. They were invaluable fore tuning. They won’t work long with oil in the fuel like a two stroke might have .the o 2 sensor does not like to get wet with anything gas water or oil. They are about $60 themselves. I flooded one of the hot rods accidentally and trashed an o2 sensor. These are used in our every day modern cars some have many more than one to maintain emission quality. I use it for tuning the carbs. You could see each circuit in the carb as it worked. A vacuum boost gage above and below the blower monitored pressure and vacuum so you could see the circuits working at all times and conditions. Originally I had a spread sheet so I could monitor test results . The cat converters take care of a lot of contaminates so protect those after the cat but the forward ones get hosed occasionally. Viewing or reading spark plugs like we did in the old days probably wouldn’t be fun on a model 18 cyl radial. I can’t imagine how plugs were changed or even servicing a Corsair on some sandy airfield in the pacific. It’s probably no wonder why these planes had 50 gallons of oil on them. My father in law said there was never much left after a mission. No oil change necessary just fill the tank and get ready for the next mission.


Bentwings said:


> Hi, I thought I might have described hoe the 6-71 and other gmc blowers work in the real world
> So here goes I can get a little long winded when I get into one of my favorite bench racing or shop chats
> 
> first the common application is on streetrods. These blower are pretty big so they often stick out of the hood a ways. For street use modified carbs are used. Holley makes special modified ones you can buy o
> 
> i ws in the middle of a reply and a spam call came in and cut me off so if a reply comes that you don’t understand just delete it. I start over. 6-71 and others like them are pretty big so they stick out of the hood quite a ways. Add carbs and scoop and you get quite an impressive unit. So how does it work? Carbs are normally mounted on top of the blower so they are called draw through. The blower pulls air and fuel through the carb just as normal. At idle the carb acts as normal seeing a vacuum of 15 or more inches. Since only a limited amount can go through there is vacuum in the intake manifold again 15-17 inches. Some will argue this but my cars have had vacuum boost gage on bothe carb and manifold for a long time. When you open the throttle more air/fuel goes in and vacuum drops ubtill you open the throttle far enough then you begin to get boost in the manifold. Now interesting enough there is a huge flow of air through the carb it continues to do it’s job until you exceed its capacity then you begin to see vacuum between the blower and carb. As though the blower isn’t there. You can clearly see this if you have dual vacuum boost gages.I could write a book on what goes on and tuning . I’m not the authority on this but I’ve been very successful puttin 30k miles on my street rods and 200k plus on factory supercharged cars. I. Now tuning. Pulling air and fuel through the car lubricates and cools the blower some. There are inter coolers available that boat guys use these add another’s couple inches to height so not real practical for street use. Blower are great mixture atomizers. You get pretty even mixture in each port and carb calibrated air fuel ratio.I use a gage for this to 0 2 sensor it’s used for accurate tuning adjustment just as modern EFI does. Is just the brain is in my head not an electronic box.
> Now lighting the mix is another story . Race cars have used magnetos for many years. Of late there are electronic ignitions that have many features I’ll leave for another day. Roots blower are pretty easy to work with. Now modeling presents another issue. These font scale very well it’s hard to get a small one to pump aid under pressure as you can see in the nice example the gentleman that modeled the screw compressor or blower. Clearances become very critical snd just getting enough air into the unit is hard. This was discovered ver early in the early diesel development. So centrifugal blowers and turbos were developed to force additional air into the gmc blower. This compound supercharging. It could be done in a model but it’s quickly apparent how complicated this could get. Plus you still have machining tolerances to deal with.
> we use a highly developed mechanical fuel injection on the race cars. Grossly simplified its similar to glow fuel model enginges carbs. Basically a barrel valve with a threaded needle valve for fuel control fed with light fuel tank pressure to provide fuel at all time not depending on vacuum assist. In modern race applications ther is a high pressure fuel pump and various pressure/volume control devices. A percentage of fuel is injected above the blower rotors to provide sealing and cooling of the mixture the rest is sprayed into the ports as fine mist the ratios determine power and. Oolong effect.this is well beyond discussion here. Nitro and alcohol do all kinds of things in engines. Sometimes very bad thingsLOL. I’ll try and post a couple pictures of my Streetrod willys. I also have a couple pictures of a friends motor and supercharger ver simulate to mine.
> byron


my plan is to build a 1/5 or maybe smaller printed model blower. Additionally I’d like to create some of the development models like the 8-71, 10-71,12-71 then add the high helix models. I know it sounds ambitious but it’s a hobby, right. I talked to a printer guy Friday and he said he could work with me optimizing modeling and printing. He also does metal printing. He said that in metal it might be possible to print close enough tolerance to make the models reasonably efficient. He is familiar with the blower and has seen the drag racer versions in action. I know that when you scale things down some things can get too smal to be practical so these can be modified for structural integrity. Turbos snd centrifugal blowers/superchargergets just don’t work very well when scaled down as it’s hard to spin them fast enough to really produce much boost. A positive displacement blower like these can work and there have been a few made by the model engine companies. A metal printed one could be made so sealing rotor strips could be fitted just like the full size. However you would have to create a slitting device to make the strips they would be pretty small so a knife like thing could probably be made. That’s getting too far ahead.  I’ve also got a planetary gear set or kit to model a changeable ration gear drive. It’s plastic but the gears are all available as metal gears on the internet. I wouldn’t want to try and drive anything but a plastic scale model at any big overdrive like we used in racing but a bench top demo would be fine. A 4 axis cnc mill could make impressive rotors pretty easily as well as a nice case. It would be really cool to see some of the recent V12 engines with a scaled gmc blower on them. Conley already makes a V8 with supercharger. Need to get back to my hobby. 
byron


----------



## Bentwings

Bentwings said:


> I know it would be an added expense but there are relatively inexpensive air fuel ratio stand alone gage systems available I had one in several of my supercharged streetrods. They were invaluable fore tuning. They won’t work long with oil in the fuel like a two stroke might have .the o 2 sensor does not like to get wet with anything gas water or oil. They are about $60 themselves. I flooded one of the hot rods accidentally and trashed an o2 sensor. These are used in our every day modern cars some have many more than one to maintain emission quality. I use it for tuning the carbs. You could see each circuit in the carb as it worked. A vacuum boost gage above and below the blower monitored pressure and vacuum so you could see the circuits working at all times and conditions. Originally I had a spread sheet so I could monitor test results . The cat converters take care of a lot of contaminates so protect those after the cat but the forward ones get hosed occasionally. Viewing or reading spark plugs like we did in the old days probably wouldn’t be fun on a model 18 cyl radial. I can’t imagine how plugs were changed or even servicing a Corsair on some sandy airfield in the pacific. It’s probably no wonder why these planes had 50 gallons of oil on them. My father in law said there was never much left after a mission. No oil change necessary just fill the tank and get ready for the next mission.
> 
> my plan is to build a 1/5 or maybe smaller printed model blower. Additionally I’d like to create some of the development models like the 8-71, 10-71,12-71 then add the high helix models. I know it sounds ambitious but it’s a hobby, right. I talked to a printer guy Friday and he said he could work with me optimizing modeling and printing. He also does metal printing. He said that in metal it might be possible to print close enough tolerance to make the models reasonably efficient. He is familiar with the blower and has seen the drag racer versions in action. I know that when you scale things down some things can get too smal to be practical so these can be modified for structural integrity. Turbos snd centrifugal blowers/superchargergets just don’t work very well when scaled down as it’s hard to spin them fast enough to really produce much boost. A positive displacement blower like these can work and there have been a few made by the model engine companies. A metal printed one could be made so sealing rotor strips could be fitted just like the full size. However you would have to create a slitting device to make the strips they would be pretty small so a knife like thing could probably be made. That’s getting too far ahead.  I’ve also got a planetary gear set or kit to model a changeable ration gear drive. It’s plastic but the gears are all available as metal gears on the internet. I wouldn’t want to try and drive anything but a plastic scale model at any big overdrive like we used in racing but a bench top demo would be fine. A 4 axis cnc mill could make impressive rotors pretty easily as well as a nice case. It would be really cool to see some of the recent V12 engines with a scaled gmc blower on them. Conley already makes a V8 with supercharger. Need to get back to my hobby.
> byron


After looking at the printed screw blower I’ve backed away from a similar thought.
After seeing a couple of new v 12 enginges I think it would be a natural to add a 6-71 style appropriately scaled to one of these.   There are countless YouTube stories of supercharging Briggs & Stratton engines most unsuccessful. One even went far enough to add a dyno to test real hp gain. This is a pretty easy thing to add. It’s much easier to deal with carbs on this style supercharger as opposed to centrifugal or turbo as they will be draw through rather than blow through so dealing with fuel pressure is much easier. 
byron


----------



## mu38&Bg#

The issue with turbos is the smallest units available are still good for something like 80HP, they are poorly matched to small singles.


----------



## Kasey

Bentwings said:


> I know it would be an added expense but there are relatively inexpensive air fuel ratio stand alone gage systems available I had one in several of my supercharged streetrods. They were invaluable fore tuning. They won’t work long with oil in the fuel like a two stroke might have .the o 2 sensor does not like to get wet with anything gas water or oil. They are about $60 themselves. I flooded one of the hot rods accidentally and trashed an o2 sensor. These are used in our every day modern cars some have many more than one to maintain emission quality. I use it for tuning the carbs. You could see each circuit in the carb as it worked. A vacuum boost gage above and below the blower monitored pressure and vacuum so you could see the circuits working at all times and conditions. Originally I had a spread sheet so I could monitor test results . The cat converters take care of a lot of contaminates so protect those after the cat but the forward ones get hosed occasionally. Viewing or reading spark plugs like we did in the old days probably wouldn’t be fun on a model 18 cyl radial. I can’t imagine how plugs were changed or even servicing a Corsair on some sandy airfield in the pacific. It’s probably no wonder why these planes had 50 gallons of oil on them. My father in law said there was never much left after a mission. No oil change necessary just fill the tank and get ready for the next mission.
> 
> my plan is to build a 1/5 or maybe smaller printed model blower. Additionally I’d like to create some of the development models like the 8-71, 10-71,12-71 then add the high helix models. I know it sounds ambitious but it’s a hobby, right. I talked to a printer guy Friday and he said he could work with me optimizing modeling and printing. He also does metal printing. He said that in metal it might be possible to print close enough tolerance to make the models reasonably efficient. He is familiar with the blower and has seen the drag racer versions in action. I know that when you scale things down some things can get too smal to be practical so these can be modified for structural integrity. Turbos snd centrifugal blowers/superchargergets just don’t work very well when scaled down as it’s hard to spin them fast enough to really produce much boost. A positive displacement blower like these can work and there have been a few made by the model engine companies. A metal printed one could be made so sealing rotor strips could be fitted just like the full size. However you would have to create a slitting device to make the strips they would be pretty small so a knife like thing could probably be made. That’s getting too far ahead.  I’ve also got a planetary gear set or kit to model a changeable ration gear drive. It’s plastic but the gears are all available as metal gears on the internet. I wouldn’t want to try and drive anything but a plastic scale model at any big overdrive like we used in racing but a bench top demo would be fine. A 4 axis cnc mill could make impressive rotors pretty easily as well as a nice case. It would be really cool to see some of the recent V12 engines with a scaled gmc blower on them. Conley already makes a V8 with supercharger. Need to get back to my hobby.
> byron



By "model" do mean on a 3D printer? I have done that and built 2 of them, each as a 2 vane  rotor pumping about 240ccs per vane stroke. Made one in PLA and the other in ABS on steel shafts and ball bearings with seals. Run both under my overhead drill to test them. Have fitted carbon graphite vanes, 71 x 50 x 5 mms. Works well but is very noisy. Not sure if that comes from the housing or the vanes slamming back into the rotor as their slots may be too shallow. Both are run in now but Will not have much of a practical service life because of the plastic rotor and housing.


----------



## Bentwings

That sounds exactly what I was planning on doing. It’s been awhile since I’ve used solid works so I’m having to relearn some but it’s coming back. I have access at least for a while but eventually I’ll probably have to go to fusion 360 to stay up to date. I doubt we will get into cnc in our small shop as we just don’t do enough to justify it. It’s easier to just take a file to a local shop and have it done.  The metal printed one sounds like it could work but tolerances might not be good enough. A metal one with stripped rotors could probably blow a head right off a Briggs. Make a nice video. LOL.
Buron


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## Bentwings

I want to add just a thought of my ultimate plans for this project.
While we were into alcohol funny car racing the west coast hot shots began really optimizing the blown alcohol motors. On guy dug up and old dump used for really big industrial stationary engines . With some hot rod engineering he converteted it to high enough capacity to handle in excess of 2,000 hp. And he began getting the most from the hemi on alcohol. Ultimately testing a top fuel engine into reportedly a huge explosion in his shop. As part of this the bigger 10,12, and 14 71 blowers came about. More boost is better right. Alcohol happens to be far less sensitive to detonation so more air and more alcohol make more power. Indeed they beat the tail out of us mid westerners ubtill we began getting their old used stuff.LOL

the blowers got longer and longer. But how did they make cases and rotors? Well you can easily make case extensions but cncstill was not readily available then. So the question was where or how were the long rotors made? After a few blower explosions it was discovered that the rotor shafts were much longer and sections of rotors had been added to make longer rotors. The extra section were pinned to the shafts ultimately this failed in spectacular fashion. Then cnc entered the picture and billet rotors became possible.
So I would like to just model this progression ultimately creating a 14-71 blower with extended case. Today the model can be printed and for the hard core a metal printed version could be made. I don’t intend to build a model blower dyno at this point as I probably don’t have deep enough pockets for this. Blower synod exist it’s hard to believe how much hp it takes to drive these on a top fuel car. There are numbers floating around suffice it to say it’s huge. You have to wonder how the belt can transmit that much power. They don’t for long and are often replaced each run. They break or strip the teeth off. Sometimes break the pulley. My Streetrod went 30k miles on a belt with no wear showing. The pulley on the crank was nearly worn out from road sand and dirt but the belt was fine. I should have purchased a hard anodized pulley to start and there would have been little wear on it. 
snyway I just want to model some history in the race things we dealt with years ago.

so that’s my add in. I need to get back tocadd modeling so I can move on to plastic models. I’m really limited in the shop due to vision issues. Probably as much of a hazard to others as well as myself. Best to let me work on the key board. Bad enough I can barely see these keys. I have to use a card or have someone else write the check out so I don’t put too many 0’s or1’s in the amount box.
Byron


----------



## Bentwings

Bentwings said:


> I want to add just a thought of my ultimate plans for this project.
> While we were into alcohol funny car racing the west coast hot shots began really optimizing the blown alcohol motors. On guy dug up and old dump used for really big industrial stationary engines . With some hot rod engineering he converteted it to high enough capacity to handle in excess of 2,000 hp. And he began getting the most from the hemi on alcohol. Ultimately testing a top fuel engine into reportedly a huge explosion in his shop. As part of this the bigger 10,12, and 14 71 blowers came about. More boost is better right. Alcohol happens to be far less sensitive to detonation so more air and more alcohol make more power. Indeed they beat the tail out of us mid westerners ubtill we began getting their old used stuff.LOL
> 
> the blowers got longer and longer. But how did they make cases and rotors? Well you can easily make case extensions but cncstill was not readily available then. So the question was where or how were the long rotors made? After a few blower explosions it was discovered that the rotor shafts were much longer and sections of rotors had been added to make longer rotors. The extra section were pinned to the shafts ultimately this failed in spectacular fashion. Then cnc entered the picture and billet rotors became possible.
> So I would like to just model this progression ultimately creating a 14-71 blower with extended case. Today the model can be printed and for the hard core a metal printed version could be made. I don’t intend to build a model blower dyno at this point as I probably don’t have deep enough pockets for this. Blower synod exist it’s hard to believe how much hp it takes to drive these on a top fuel car. There are numbers floating around suffice it to say it’s huge. You have to wonder how the belt can transmit that much power. They don’t for long and are often replaced each run. They break or strip the teeth off. Sometimes break the pulley. My Streetrod went 30k miles on a belt with no wear showing. The pulley on the crank was nearly worn out from road sand and dirt but the belt was fine. I should have purchased a hard anodized pulley to start and there would have been little wear on it.
> snyway I just want to model some history in the race things we dealt with years ago.
> 
> so that’s my add in. I need to get back tocadd modeling so I can move on to plastic models. I’m really limited in the shop due to vision issues. Probably as much of a hazard to others as well as myself. Best to let me work on the key board. Bad enough I can barely see these keys. I have to use a card or have someone else write the check out so I don’t put too many 0’s or1’s in the amount box.
> Byron


I’m sorry instead of dump above I meant dyno. That makes more sense. Like I said I’m a hazard.
Byron


----------



## Bentwings

Those of you pursuing this project should go to a site that shows a rebuild or build assembly of a stock blower. There are seal areas between the rotors not shown on the models they are called the CC. Clearances. There is a spec for these it’s a common measurement we used to use to check the condition of a used blower or modified one. Often this area got scuffed beyond usefulness. Modern blowers have nylatron seal strips in these areas too that need servicing eventually.  These seal surfaces need to be included in the rotor sketch drawing befor you extrude it or twist it otherwise it will be nessary to go back and edit the sketch which becomes a pain.  Just so you know it’s not just a round bump or three as most are.  If you are planning on seals well this is where they go. In the old days this was a nasty machining setup to make the grooves. Modern cnc makes it easy. I’m not sure printing can make this accurately so I’m looking at more flexible sealing materials. Just making a seal cutter tool could be another shop exercise.  I haven’t got this far yet.I don’t think I’ll do the helical gears unless I can find a down load file. The helical gears are so the CC clearances can be adjusted by shimming the gears. These shims used to come in a blower overhaul kit. Or you could Jude arbor shims.getting printed gears to mesh close enough might be an issue to be dealt with when the time comes.  You don’t want back lash especially in model size blower. 0-0 would be the clearance neededso any wear on the gears will quickly wipe out rubbing rotors. 
so the whole project is just that a big model hobby project with lots of pit falls.
I’m going out this weekend and make some measurements then get back to developing some kind of sketch.  The initial model I saw done on the internet looked pretty easy but all this added detail has complicated it considerably. I don’t know if I’ll post a video or not . I may make a detailed drawing of the end of the rotor but I’ll have to see if this is practical. I’m having to relearn some modeling things that were not available in my working days.  
mice got two other projects to keep in mind too.
So anyway I’m open to challenge or questions and comments.

byron


----------



## Bentwings

Kasey said:


> By "model" do mean on a 3D printer? I have done that and built 2 of them, each as a 2 vane  rotor pumping about 240ccs per vane stroke. Made one in PLA and the other in ABS on steel shafts and ball bearings with seals. Run both under my overhead drill to test them. Have fitted carbon graphite vanes, 71 x 50 x 5 mms. Works well but is very noisy. Not sure if that comes from the housing or the vanes slamming back into the rotor as their slots may be too shallow. Both are run in now but Will not have much of a practical service life because of the plastic rotor and housing.


You should hear the noise a full size 8-71 makes when being driven 50% over crank speed wide open throttle even with full fire suit and ear plugs it’s deafening. My Streetrod could be heard blocks away the few times I got after it


----------



## Kasey

Bentwings said:


> You should hear the noise a full size 8-71 makes when being driven 50% over crank speed wide open throttle even with full fire suit and ear plugs it’s deafening. My Streetrod could be heard blocks away the few times I got after it


I'm shortening the vanes by 5 mm and curving the base; that may put a cushion of air there to soften their return, I hope.


----------



## Kasey

Yet mine runs at only 1/2 crank speed and it's intolerable without ear muffs. Here is a photo of it dismantled. I need to put a tin liner in now as the ABS vane contact surface is scraping off from the vanes rubbing on it. (shows only one of 2 vanes.)


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## Bentwings

I think it was noted above about the OS max and YS pattern motors of years ago. I loved pattern planes and flying them. Ironically it was one of the few sports I never won or excelled at. I always seemed to come up a point short at the end of the day. I eventually became way too expensive and time consuming to build models. I never ha the OS supercharged or the YS I always thought they were cool but my shank motors ran perfectly. I was a Dirty birds fan an had a bunch of them. I made Fiberglas canopy mold and used muffled tuned pipes on them. I had a few Brody UFO an a couple Arrows. The forty birds was the fastest but I think the UFO SEEMED TO HANDLE THE increasing weight and the three blade props that became necessary for noise restrictions.I wasn’t into pylon racing but one club sponsored an unlimited event each year. The DirtyBirty did well as it could turn well especially with my combat flaps copied from p51 and Corsair. The best win though was with my twin .7.5 ducted fan motored twin. It was really fast and sported combat flaps sealed control surfaces with buried tuned pipes fuel pumps and healthy nitro fuel. Those were expensive motors in the day. Ducted fan jets were just getting popular so I fell in with that crowd as I could get nitro since we ran a top fuel funny car too. I live just across the road from the flying club field so I could go and fly every night if I wanted to. I don’t know how many motors I went three but it was a bunch.it seemed like I’d build a couple racer motors for the week end and a few for the Rc planes in my spare time.  Rc model costs were small peanuts compared to the race car stuff. A single racer piston cost more than a Hano motor. Sponsor and match race money paid our race budget. I wish I had some of that now instead of memories.LOL. 
mom hoping this blower project can be a fun bench racing and shop talk event. There aren’t too many of us that grew up in the shop and went on to engineering and aerospace stuff. 
sorry I get off topic occasionally. I just enjoy talking about mechanical stuff and making things interesting. It’s fun that my boys have picked this up too one is a pro bike racer, one has a big landscaping business. Another has automotive business and race car shop on the side with smalll machine shop. One plays town baseball. He knows everything about the game. Played in little league World Series. So some of the “0ld dad stuff” has rubbed off. Being old isn’t so bad after all.
Off the soap box for now.
Byron


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## Badhippie

Talk about noise you should hear a duel blower setup on a EMD locomotive engine. BTW they are even bigger then a 14:71 blower. In notch 8 under load you can not even hear yourself think 
Thanks 
Tom


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## Kasey

ANY IDEAS ON HOW TO MAKE IT QUIETER? My rotor is only 80mm D and 70 mm long, with 2 vanes. Both the rotor and housing are made of 3D printed plastic.only the vanes are carbon graphite. I've had it running semi-dry at about 2000rpm +.


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## mu38&Bg#

Install in intake muffler to attenuate the pulsing air flow. If you have mechancial noise that's a different story.


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## Bentwings

I used a 6-71 on my Streetrod and drove it everywhere for 30k+ miles. Going down the road with two flow thru air cleaners in the big BDSacoop you could only hear a small whine. Standing along side idling again it was minimal. Mostly determined by how tight the belt was. Too tight made a little more noise. Full throttle 6000 rpm it was a streak ing sound you could hear blocks away. 3” exhaust made a terrific roar. 15” wide tires spinning on pavement made a sound all their own.LOL beside paving the street with black rubber marks.  A friend now has a similar Streetrod with even more power than mine and when he gets after it you appreciate the 5 point racing seatbelt and form fitting seats. I never really felt the cars were that fast driving but riding passenger changes the picture.  I drove fuel gunny cars for quite a while and the acceleration boot kinda went away after a while and you found you could look around as you were going down the track. It got your attention when something went wrong like a clutch explosion right between your feet or a blower explosion and instant removal of the windshield replaced by a blast furnace. Those time it was reassuring when a $1000 fire suppression system did its job. I drove my street rod sensibly often going to the grocery store and cruising back roads with the other guys. There was no crazy driving on rod cruises. We stayed together as a group followed the road rules . Basically had a good time together.
Here is my friends Streetrod 637 hp 2800 pounds. It’s a 1954 Henry j two door sedan 

byron


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