How do I model a supercharger rotor?

[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.

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]

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]

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

 

[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]

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]

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]

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.)

 

[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

 

[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

 

[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 +.

 

[mu38&Bg#]

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

 

[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