# Camshaft lobe timing



## JohnnyGTR34 (Apr 14, 2013)

Hello!

  I am new to this forum, and I have a question. I am currently designing a SOHC 16-valve miniature V8 engine that I plan to build after I finish the CAD model. There is one major problem that I am running into, and that is how to position the camshaft lobes for proper timing. As of now the crank is cross-plane and I have no preference for direction of rotation (If there is a specific counterclockwise or clockwise direction, I'd like to know which is best) I plan on having it run on Nitro, so 8 glow plugs will be used in the favor of simplicity. 

  Basically what I would like to know is where can I find a chart or some reference for camshaft lobe positions? The camshafts rotate the same direction as the crank, also.

Here is a photo of the current design if anyone is interested. Thank you for having a look!


----------



## stevehuckss396 (Apr 14, 2013)

This was just covered in a thread about 3 weeks ago. I'll see if I can find it


----------



## JohnnyGTR34 (Apr 14, 2013)

Oh, was it? Thank you! I can delete this thread if necessary


----------



## Dousi (Apr 14, 2013)

cam/valve timing

I've asked this question, this is the thread.


----------



## canadianhorsepower (Apr 14, 2013)

try this

http://www.tildentechnologies.com/Cams/CamPerformance.html


----------



## dman (Apr 14, 2013)

http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/ this is for the specs. 

as for what lobe goes where, you gotta come up with a firing order based on your crank design first. there can be 16 different working combinations for any v8. the most common is counter clockwise viewing the crank from the rear of the engine with the cylinders numbered evens on the right bank, odds on the left, again this is viewed from the back the most common order is 1-8-4-3-6-5-7-2 but 1-8-7-2-6-5-4-3 is gaining popularity on modern engines and happens to be the same as one of the two ford firing orders but ford numbers the cylinders wrong so it ends up looking different.... and the third popular firing order is 1-8-7-3-6-5-4-2

1-8-7-2-6-5-4-3 is said to have more even bearing loading and now there is some rumors that it has better thermal characteristics reducing hot spots.

1-8-7-3-6-5-4-2 is said to make the most horsepower. probably having to do with crank harmonics and intake interference. but 1-8-7-2-6-5-4-3 is also becoming a popular firing order for performance engines. 

if you designed your cross plane crank the same as a conventional american v-8 one of these will work for you.


----------



## Till (Apr 14, 2013)

JohnnyGTR34 said:


> in the favor of simplicity.


If you got questions on cam lobes, syncronizing eight carburetors will be a giant challenge for you. If one of your eight carburetors runs on too lean mixture, the piston  will get hot, expand, seize and destroy half of your engine including the  crankshaft.
In favor of simplicity, i strongly recommend to use only one single caburetor with a 8-way split manifold in the beginning. You can upgrade later. This way you can easily change different commercially available carburetors until your engine runs fine, which rules out the mayor source of problems (carburetor). Then the next step is to adapt to a two carburetor design feeeding a cylinderbank each and so on... depending on your patience... however, using an existing cam design from commercially available plans will be the easiest solution for the question in post 1.


----------



## stevehuckss396 (Apr 14, 2013)

Here it is. The numbers below are lobe centers.

Your cam would have #1 exhaust at zero degrees and intake would lag 110 degrees so it would be at 250 degrees. #8 being next would lag by 45 degrees so 315 degrees BUT the cylinder bank is 90 degrees back so the lobe for any even cylinder needs to lag by an extra 90 degrees. #8 would be Zero - 45 - 90 so it is at 225 degrees and its intake lags by 110 so 115 degrees. Draw up a degree wheel with the segments numbered clockwise and start laying it out. 


Cylinder# / Intake degree / Exhaust degrees

1 / zero / 250
8 / 225 / 115
4 / 180 / 70
3 / 225 / 115
6 / 90 / 340
5 / 135/ 25
7 / 90 / 340
2 / 315 / 205


----------



## JohnnyGTR34 (Apr 14, 2013)

I agree, but I may find it more challenging with the resources available to make an effective 8-way split manifold. It's still in the development phase however, so anything can change so I may redo the intake setup.

To steve: Thanks! This should help greatly.


----------



## JohnnyGTR34 (Apr 14, 2013)

Till: Also, I figured that the displacement for each cylinder was roughly 3.1 cc. Is using a carburetor designed for 2.5 - 3cc engines logical for each cylinder of my engine, or would it being a four stroke make it completely different?


----------



## dman (Apr 14, 2013)

looking at your rendering, it appears you have direct valve actuation, no rocker arms. this may be ok but the point of rockers is to control the forces of the rotating cam trying to bend the valve stem. in full scale direct actuation works but only if the valve springs sit in a bore with a cup over them guided in the bore. the easiest way to do this is the way toyota, gm and fiat did it on certain engines which is to make the head in several pieces. a head that has the cooling passages and valves and guides, then on top of that a cam box that has a bore for each valve and a cam bore above the spring bores then either bearing caps to hold the cam in or a valve cover with the cam bore machined into it. if the cam boxes are cast aluminum and the cam is chrome plated or made from a alloy steel with good corrosion resistance and precision ground you may be able to use the aluminum as the bearing surface like most manufacturers do today. 

notice that bores for the valve cups in the pic below? but you can still see under it to the springs. that's so oil doesn't get trapped in the bore and lock up the valve, it needs to drain so things move and you dont leak oil past the guides. but without casting the head it will be difficult to make this feature in one piece. which is why you want to make it in two pieces. 

https://encrypted-tbn0.gstatic.com/...Ge4sLTJZaD5gNbFIZQms7988yIZhYxM42W9Iu9T3zuZWS

if you dont want to use cups and shims to set the lash you want to add a rocker and adjuster. you can move your cam bore over a little and add a pivot. the ford mod motor design would be easiest to adapt you blueprints for. you could add adjusters to either the pivot or the valve end. 

http://image.hotrod.com/f/techartic...6_02_o+valve_arrangement+on_ford_pl_heads.jpg


----------



## JohnnyGTR34 (Apr 14, 2013)

Another question, What would you recommend for lift distance? I'm not sure what is sufficient and what is too much. I'm trying to design the lobe but I don't want to design it wrong so that it may break the valve stems. Thanks for the reply dman! I'll have to look into this more.


----------



## dman (Apr 14, 2013)

JohnnyGTR34 said:


> Another question, What would you recommend for lift distance? I'm not sure what is sufficient and what is too much. I'm trying to design the lobe but I don't want to design it wrong so that it may break the valve stems. Thanks for the reply dman! I'll have to look into this more.



the flow area equals the valve area at just under 25% the valve diameter but you can go a bit more for better CD (coefficient of discharge) and more area under the curve. so 25%-30% the intake valve diameter should be good and you can make the exhaust as big as the intake even though the valve is smaller, infact the exhaust lobe is often a bit bigger than the intake for more duration and area under the curve since the exhaust timing is less critical to velocity and pressure that helps make horsepower. under 25% valve diameter and you are under using the valves, 35% intake valve diameter is about as much as you will ever see.
the exhaust valve diameter is usually 75-80% the intake valve diameter.


----------



## JohnnyGTR34 (Apr 14, 2013)

Great, sounds good. Compared to the .625 bore, how large should the valves be? As of now I have them set at .28 (about the diameter of a #5 countersunk flathead machine screw, what I will be using for the valve stem with a few modifications), is this sufficient?


----------



## dman (Apr 14, 2013)

JohnnyGTR34 said:


> Great, sounds good. Compared to the .625 bore, how large should the valves be? As of now I have them set at .28 (about the diameter of a #5 countersunk flathead machine screw, what I will be using for the valve stem with a few modifications), is this sufficient?



sounds about right. maybe you could make the intake a tad bigger but not much. basically if the valve flow charicteristics were perfect you would need an area around the valve that was 41% larger than the valve (less actually because the seat is smaller than the valve). but that's just theoretical based on cross section and many other things get in the way but it's a place to start. once the valves are large enough that you have less than that much extra room around them the flow is less efficient but the actual flow still increases with increased valve diameter to a point. just not at a rate proportional to the increase in valve area. the number you have puts you pretty close to the ideal size. and it's just a model. you're not engineering a race engine. it's certainly going to run with a valve that size....


----------



## mu38&Bg# (Apr 15, 2013)

Have you designed the glow plug hole yet? Might be better to make room for it before working on valves.

The 2.5CC carb  will be far too large for a 3.1CC four stroke cylinder. I ran a 2.5CC  Rossi slide carb on a 15CC single cylinder four stroke (OS FS-91S) and  it made full power.If the engine will be run without load, even  smaller will be better. Carbs are really sized for the amount of power  the engine makes(airflow). Putting a carb from a 0.5-1.5HP engine (most  2.5CC glow two stroke car engines) onto a cylinder that will make maybe  0.1-0.2HP, will result trouble in tuning and fuel draw.

Greg


----------



## JohnnyGTR34 (Apr 15, 2013)

Hmm, I guess I never really thought of that. Will it run off a single 2.5cc carb if the engine is 25 cc? (roughly).

dman: I agree. Thanks for your input guys! it really helps.


----------



## JohnnyGTR34 (Apr 15, 2013)

dieselpilot said:


> Have you designed the glow plug hole yet? Might be better to make room for it before working on valves.



And to answer your question, yes I have! It will accept a standard 1/4-32 glow plug. Thanks for the support you guys! I'm learning quite a lot that I did not know about IC engines ;D


----------



## mu38&Bg# (Apr 16, 2013)

JohnnyGTR34 said:


> Hmm, I guess I never really thought of that. Will it run off a single 2.5cc carb if the engine is 25 cc? (roughly).



I would say a single carb of that size is enough for display running.

Will you be using bucket cam followers?

Greg


----------



## dman (Apr 16, 2013)

JohnnyGTR34 said:


> Hmm, I guess I never really thought of that. Will it run off a single 2.5cc carb if the engine is 25 cc? (roughly).
> 
> dman: I agree. Thanks for your input guys! it really helps.



if you have a common plenum the air demands are much smaller, individual cabs need to be big to supply the peak air demand but the air is only flowing about 180deg out of 720deg rotation. with a common plenum and 4 or more cylinders the air demand is more constant so a 2.5cc 4 stroke carb could in theory power a 10cc 4cyl engine to similar speeds. also the rpm range may be different and the effective displacement of a 4-stroke is half that of a 2-stroke since it take 2 revolutions. that and glow engines have pressurized fuel tanks so they dont need velocity in the carb as much... it all adds up.


----------



## mu38&Bg# (Apr 16, 2013)

If the engine will never make more torque than to overcome it's own friction, it doesn't need a large carb. Glow engines do use muffler pressure in the tank, but for proper function a good venturi signal is essential. This is true of any carb throttle.

Greg


----------



## Till (Apr 18, 2013)

JohnnyGTR34 said:


> Till: Also, I figured that the displacement for each cylinder was roughly 3.1 cc. Is using a carburetor designed for 2.5 - 3cc engines logical for each cylinder of my engine, or would it being a four stroke make it completely different?


 Well I will start one last try to convince you of the great benefits of a single caburetor design. But to add further information, I will try answer your question first  



 The carb size is not linked directly to total engine or cylinder displacement. The size of the carb is determined by the amount of air-fuel-mixture needed. (Thus, four-strokes need smaller carbs than two-strokes of equivalent size and rpm).
 Small carbs are good for small air requirements, but they are restrictive to higher amounts of air. With small amounts of air, a big carb will not be able to vaporize fuel into the air properly, so you can't archieve smooth running at low engine rpm, when air requirements a very small..
 So a small, high-revving engine with bad idle requires a similar carb as a big, low-revving engine does for sufficient performance.


 &#8594; Long stroke engines with camshaft timings focused on lower revs with a high amount of low end torque require smaller carbs than short stroke engines with wild cams do.


 I hope you now understand why you can't pick the right caburetor by simply taking one from an engine with similar displacement. You have to choose one that fits your engine's individual charateristics. Small changes on the carb setup cause huge differences.


 So I strongly recommend one single carb for all eight cylinders in the beginning.  
 Only one carb to exchange,
  only one to adjust.
 And the best point: No need to syncronize.


 If you still want to go for eight carbs in the beginning, a good idea is to build a singlecylinder engine with 1/8 of displacement first so you can test different carb designs and sizes on that single cylinder to archive smooth run at idle and desired maximum poweroutput (could be tested easily by using a propeller and mesuring max rpm). Then use eight of these carbs on the eight cylinder engine.


Ok, one last try: A single carb for all eight cylinders will produce a deeper and more vibrant resonance of the induction sound because of the combination of bigger  induction manifold volume and longer runners.


----------



## JohnnyGTR34 (Apr 19, 2013)

Till said:


> Well I will start one last try to convince you of the great benefits of a single caburetor design. But to add further information, I will try answer your question first
> 
> 
> 
> ...




Yeah, I see your point! I have already begun designing a single carb intake manifold for my engine that will be 3D printed with the help of a friend of mine. Should I have the inlet of the manifold be centered over the block or can it be towards the front?


----------



## Till (Apr 20, 2013)

Suggestion for a layout:
 carb-chamber-runners


 Connect all intake-port runners to one central chamber, make sure all runners have the same lenght. Make sure the chamber has at least the volume of all runners combined.


 This way you can assume that the partial pressure in the chamber is the same everywhere in the whole chamber, so each runner inducts the same amount of air+fuel mixture (very good!)


 The air will oscillate in the runners, so at a small bandwith of engine rpm, this provides a dynamic supercharging effect.


 For a low rpm high torque concept, choose long runners with a small cross section. This will greatly improve carburetion at idle speed, too.
 For a high rpm high output power concept, choose short runners with a bigger cross section.


 Hint: If the chamber is connected to the runners via flexible rubber tubing, you can figure out the perfect runner-lenght by exchanging with tubes of different length (all eight tubes must be of the same length every time, of course). Measure propeller speed at different throttle settings (1/4...½... fully open) to estimate the best solution.


With rapid prototyping, manufacturing &#8222;good&#8220; runners is an easy task. So make sure the junctions of the chamber with the runners have smoothly rounded transition and that the runners are slightly tapered towards the inlet ports.


 For a more aggressive throttle response, the chamber could be made smaller, but this makes the equal distribution of air-fuel mixture to each cylinder much more difficult to archive (so don't do this on your first modelengine).


----------



## JohnnyGTR34 (Apr 25, 2013)

Till said:


> Suggestion for a layout:
> carb-chamber-runners
> 
> 
> ...



Thanks, Till! I was wondering how equal distribution of fuel would work without the proper manifold. So, if I have a 7/32" intake port diameter, is that sufficient? I would like it to have a deeper, low idle sound.

I figured out the timing for each camshaft, thanks for your help you guys!


----------



## canadianhorsepower (Apr 25, 2013)

> Hint: If the chamber is connected to the runners via flexible rubber tubing, you can figure out the perfect runner-lenght by exchanging with tubes of different length (all eight tubes must be of the same length every time, of course). Measure propeller speed at different throttle settings (1/4...½... fully open) to estimate the best solution


 
I think this is a truck load of work for nothing specialy on a model engine.
In theory it's sound great but in reality it's BS for all of this to be 100% effective all cylinder must be identical.:fan:
Exactly same picton,rod and crank weight( different weight=different acceleration=not same carb set up) this is also real foe valve leeking,
intake, exaust and combustion chamber scavengingthat must be identical for that to work.

In Nascar with $80,000. motor and all the equipement they have they can't do it. What they are doing after all the theory is assemble and running they
are using a special tool calculating a v belt flexing that is equal to piston acceleration and from the result they change valve lash to equal evething.

It's a known fact that nascar motor camshaft have more duration on all the four cylinder at the 4 corner then the middle one


----------



## mu38&Bg# (Apr 25, 2013)

Tuned intake runners on model engines are fairy tales. The lengths required are not significantly different than full scale.

Luc, that's due to the types of manifolds used on Nascar engines.


----------



## canadianhorsepower (Apr 25, 2013)

dieselpilot said:


> Tuned intake runners on model engines are fairy tales. The lengths required are not significantly different than full scale.
> 
> Luc, that's due to the types of manifolds used on Nascar engines.


 
Yes I know  but I guess "faity tailes" is a better wording for model engine


----------



## JohnnyGTR34 (Jun 7, 2013)

Hey guys! It's been a long time. Thanks for your support, I figured everything out! Right now it's a twin turbo SOHC mini V8, the ball bearing turbos from turbokeychains.com. (I know it won't create any meaningful boost, but it's just so cool)


----------



## gbritnell (Jun 7, 2013)

Johnny,
You have been given some useful information from all the respondents. I have been building miniature engines for a long time and still don't have all the answers. Each engine has it's own characteristics and therefore it's own fuel/air needs. Your last posting about putting toy turbos on and engine is upsetting to me because the people on this board were trying honestly to help you with a problem and you more or less throw all that aside. All I can tell you is when you get your engine finished to the point of putting some type of fuel system on it you think that trying to adapt and tune a carb to it is tough then adding supercharging of any type will be a nightmare. 
gbritnell


----------



## JohnnyGTR34 (Jun 8, 2013)

Well this thread is about camshaft lobe timing and I can say that with the help of the kind individuals on here, I figured it out. So I'm not throwing it completely aside, but I have taken into consideration all of the carburetor and air intake suggestions that everyone has provided and modified the engine as such. So I am very sorry you are disappointed but I am extremely greatful that I was able to receive help from you folks. As for the turbos, They are up in the air at the moment. The turbos are cast and include a twin shield chromium steel ball bearing for the turbine shaft, and a "race" model is available for custom order (about 75$) that includes multiple strengthening and performance enhancements (like a stronger compressor blade), so I wouldn't exactly call these toys, but I have the plans modeled up so that I can remove them at any time.

Anyways, thanks for taking your time to comment on this thread and voice your opinion


----------



## John Rus (Jun 9, 2013)

Doesn't a turbo charger or super charger need a lower compresion ratio to run properly?  Other wise you might get into of worms!

John.


----------



## Septic (Jun 9, 2013)

I hope that you wont take this comment as any sort of personal attack, or insult, as that is certainly not my intention and I can understand to an extent what you're trying to do because I too have been that way inclined (even if it was 30 years ago)

It's important to push boundaries and explore limits (especially our own) but its just as important to mount our engines securely before firing them up next to the wife's china cabinet.....

I am slightly concerned that, as with a huge number of enthusiastic, talented and intelligent people, you may have been sucked into devoting your efforts and energies toward an over ambitious project that will leave you disappointed and disheartened... Especially where the project itself will consume a huge amount of time and effort on your part.

Your design focus, from what I can gather seems to be centred almost exclusively on techniques used primarily in the full sized world to increase performance e.g.  V-8, multi-carb, turbo, etc  ideas which, as I'm sure many people will agree, don't necessarily react as you might expect to being scaled down to the sizes we're talking about without using exotic materials, special fuels, incredible levels of machining accuracy and certainly not novelty turbochargers that would most likely stop the engine working efficiently enough to do anything but build up enormous levels of heat, destroying themselves and possibly damaging other components...

If my assessment is wrong, or if I've misread/understood your thread you have my sincere apologies, but otherwise, I'd encourage you to either concentrate on a far simpler V-8 if (it must be a V-8) or better still, focus your obvious enthusiasm for performance on creating a highly tuned single, or twin which would offer you a far greater sense of accomplishment and leave you with a much greater understanding of how induction, valve timing and fuelling work, so you can then go on to design powerful, multi cylinder power plants successfully.


----------



## stevehuckss396 (Jun 9, 2013)

John Rus said:


> Doesn't a turbo charger or super charger need a lower compresion ratio to run properly?  Other wise you might get into of worms!
> 
> John.



Not really. The lower the compression ratio is the more boost you can have without excessive cylinder pressure. That's the short version but there are advantages to low compression and high boost.


----------



## John Rus (Jun 9, 2013)

Whoops! I meant " a can of worms!".

Thanks, now that you mention it I do recall somthing about still being able to use higher compresion ratios.  Thanks for the clarafication.

John.


----------



## JohnnyGTR34 (Jun 10, 2013)

Thank you septic. I do agree with what you have advised me to do. I haven't started building it, it's still in the design phase and I do agree that a single cylinder would be a great deal easier. This project unfortunately has been put to the side though because I am working on my car. I hope to resume it soon!


----------



## JohnnyGTR34 (Apr 10, 2014)

Hello all, after a long break from this forum I am briefly returning. Unfortunately, I don't think this engine will ever make it to a physical model. Ive been extremely busy with my car, robotics, and have development. If I ever find time in the future, I'll pick up this project again but in the mean time I am too busy. School is keeping me very busy as well. I would like to thank all of you for your experienced advice and good intentions, and I would also like to apologize for immaturity on my part with sticking on fake turbos to my cadd model, which I quickly realized would most likely be a disaster. Anyway, thanks a lot to everyone.


----------

