Cam's LSA effect on power
#41
Originally Posted by Adrenaline_Z
Does that necessarily mean there is less overlap? These Pro Stockers run durations from 280-300 degrees at a min. of 0.050" lift.
#42
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Aparently in prostock applications they are moving away from overlap to get power up so there must be a very good reason
where I can verify this information from professionals in the Pro Stock engine
tuning business.
I'll see if I can get a direct response and post it with his permission.
#43
Originally Posted by Adrenaline_Z
I'm not aware of the valve timing trends in Prostock, but I do know a place
where I can verify this information from professionals in the Pro Stock engine
tuning business.
I'll see if I can get a direct response and post it with his permission.
where I can verify this information from professionals in the Pro Stock engine
tuning business.
I'll see if I can get a direct response and post it with his permission.
#44
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Originally Posted by CollinsAutomotive
there are in fact alot of vairiable and if this thread is going to distill down to best LSA it totally negates the conversation. there is no best overlap. There is Best overlap with each camshaft cylinder head header exhuast bore and stroke combination. What would be nice is to build a good mathmatical formula to determine what the best overlap would be for a given combination of parts.
#45
Originally Posted by CollinsAutomotive
well lets ask this question are they changing the duration of the camshaft ?
#46
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Originally Posted by CollinsAutomotive
again this will depend on the lobe sizes. But 30yrs ago prostock cams were in the 100-110 range from what i have been told. With advances in cylinder heads,Manifolds,headers exhuast and carbs and the newer lobe designs they have been getting wider and wider. that duration and RPM are much higher. Its just something a few yrs ago that made me go Hmm why did they do that. So i tried playing with wider LSA's to see if there was trend. It turns out that we started finding power on the smaller cube engines by going wider then everybody else was. The duration was going up but the overlap was being held constant. It was interesting to see the engine make alot more TQ and HP at the same RPM. there are in fact alot of vairiable and if this thread is going to distill down to best LSA it totally negates the conversation. there is no best overlap. There is Best overlap with each camshaft cylinder head header exhuast bore and stroke combination. What would be nice is to build a good mathmatical formula to determine what the best overlap would be for a given combination of parts.
Ummm yeah.... there is a set overlap that every motor likes.
Pro Stock went wider LSA for a few reasons.... most of it is RPM. You need to close the intake valve, later and later in a PS motor due to the RPM range that they run in. 10,000rpm (or more) dicates a late IVC point, plus as AdrenilineZ mentioned this much duration means lots of overlap no matter what the LSA. PS heads also run canted valves, which will always widen your LSA, and extreme example is the Hemi, and a mild example is a BBC. One more thing that people never look at is the pressure differences between the cylinder and the intake port at the RPM they are turning... Now put the valve lift and duration that is needed to get the air moving into the cylinder and you can see that 130° of overlap can cause problems.... PS wants scavenging but those motors run more on inertia/wave tuning than anything else out there, and that means you have to get everything right.
As for the early EVO, it will always hurt power, but when you have a smaller exhaust valve to fit more intake valve in the head you just can't get enough time(duration) to clean out the cylinder unless you do this. Now balance this out with the rest of the valve events, and if you need time (duration) to empty the cylinder and you have to keep overlap down, your ECL needs to be higher and now the valve opens eariler. On top of that PS motors have very good burn, but very high leads relative to that burn due to the bore and stroke ratio and the shorter and shorter rods they are running. It's not as bad as F1, but it's not very good either. The burn still happens in the same place in the crank rotation.
Bret
#47
Originally Posted by GIGAPUNK
Well other than the: as big as possible, until you're blowing too much fuel out of the exhaust valve, race car idea. Which I have no trouble believing, but let's presume I need to design A cam for my car and don't have the resources to go through 20 cams determining where that point is. Theoretically/mathmatically (not experimentally) how is it found?
I suppose you could theoretically/mathematically model the overlap/scavenging process, but to do so with any semblance of accuracy would require a non-linear Finite Element Analysis and, for the effort required to do this, you might as well run some experiments, which have already been done and I posted the results earlier (how convient!).
Furthermore, some engines have been built with extra overlap added in by using a small lobe before the intake lobe and another one after the exhaust lobe. In other words, the intake valve starts opening during the end of the exhaust stroke, then closes a little to make room for the piston, then opens like normal. The exhaust valve is also opened more after TDC to increase overlap. At least in the test that I saw, this improved power. I imagine this isn't used more because a) most people get a poor enough idle without resorting to this and b) the valvetrain dynamics are likely outside the accepted reliability envelope that we normally operate in.
Mike
#48
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Originally Posted by engineermike
Furthermore, some engines have been built with extra overlap added in by using a small lobe before the intake lobe and another one after the exhaust lobe. In other words, the intake valve starts opening during the end of the exhaust stroke, then closes a little to make room for the piston, then opens like normal. The exhaust valve is also opened more after TDC to increase overlap. At least in the test that I saw, this improved power. I imagine this isn't used more because a) most people get a poor enough idle without resorting to this and b) the valvetrain dynamics are likely outside the accepted reliability envelope that we normally operate in.
Bret
#49
Originally Posted by SStrokerAce
Yep the dynamics to run that at more than about 2000-3000rpm would pretty much make an impossible situation.
Bret
Bret
#51
Originally Posted by CollinsAutomotive
Saying gernerically however that wedge heads can't overscavenge is fairly rediculous. . . But making a genral statment that More overlap is always better is ignorant.
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From the man's finger tips:
Originally Posted by Darin Morgan
Yes all valve timing are quoted at .050". A standard Pro stock cam right now
is .568/.550 lobes 279°/306° on a 118.5 or 119.5 LC
We run as litttle as 64° of overlap at 0.050".
is .568/.550 lobes 279°/306° on a 118.5 or 119.5 LC
We run as litttle as 64° of overlap at 0.050".
Originally Posted by Darin Morgan
On average about 80% of what I talk about is not public knowledge. It really doesn't matter though. What most people consider secret is just sound mechanical engineering. As far as I am concerned, there are no secrets. If people think that by touching on specific engine design criteria and engine specs is somehow going to make them an engine builder over night or able to built and tune a Pro stock engine, they are being silly. I will tell any one, anything they want to know. You just have to ask the right questions.
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines
http://www.rehermorrison.com
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines
http://www.rehermorrison.com
#55
Originally Posted by engineermike
Well I'm glad we had this conversation then. I can't wait to relay this information to the 2 said highly competitive and record-holding engine builders so they can start making real power. . . And, yes, your example of changing LSA from 114 to 116 and gaining power is almost totally irrelevant because of the changes to IVC and EVO.
#56
Originally Posted by Adrenaline_Z
From the man's finger tips:
#57
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Originally Posted by GIGAPUNK
So Mike's theory of max overlap seems a little controversial, but I don't see anyone arguing against as much exhaust duration as possible. Which brings me to an obvious question.
What's the latest you would want an EVC?
What's the latest you would want an EVC?
Bret
#58
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Originally Posted by Adrenaline_Z
From the man's finger tips:
Originally Posted by Darin Morgan
Yes all valve timing are quoted at .050". A standard Pro stock cam right now
is .568/.550 lobes 279°/306° on a 118.5 or 119.5 LC
We run as litttle as 64° of overlap at 0.050".
is .568/.550 lobes 279°/306° on a 118.5 or 119.5 LC
We run as litttle as 64° of overlap at 0.050".
Bret
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Originally Posted by CollinsAutomotive
Well yes they are runing 65 degree of overlap but they have also realized that A there is an optimum number for a specific intake exhuast combo B that to achive that optimum number they have to move the lobe forward or backward.
engine class I have little knowledge about.
The only thing I'm disputing is the direction of overlap toward a decreasing
value. Overlap is critical for any N/A engine. The amount of overlap doesn't
concern me.
I think many people here are getting too wound up on the exact figures, instead
of understanding the basics. I personally don't give a $hit if my overlap is
a degree off, or my IVO is not optimized. I had a quarter mile goal in mind
and I've achieved that goal. That makes me happy and the fact that I
can visualize and understand the effect of a later IVC or a tighter LSA using
similar lobes.
This discussion has gone from street engine to Prostock overnight and it's
totally confusing the conversation as far as I'm concerned. Nobody is going
to get the perfect cam numbers from this thread, or any other thread for that
fact. What's right for Giga's engine, is not right for your engine, or Darin's
engine. Even from city to city, and season to season those specs are going to change.
#60
Originally Posted by Adrenaline_Z
You don't have to get defensive, I'm just supplying information about an
engine class I have little knowledge about.
The only thing I'm disputing is the direction of overlap toward a decreasing
value. Overlap is critical for any N/A engine. The amount of overlap doesn't
concern me.
I think many people here are getting too wound up on the exact figures, instead
of understanding the basics. I personally don't give a $hit if my overlap is
a degree off, or my IVO is not optimized. I had a quarter mile goal in mind
and I've achieved that goal. That makes me happy and the fact that I
can visualize and understand the effect of a later IVC or a tighter LSA using
similar lobes.
This discussion has gone from street engine to Prostock overnight and it's
totally confusing the conversation as far as I'm concerned. Nobody is going
to get the perfect cam numbers from this thread, or any other thread for that
fact. What's right for Giga's engine, is not right for your engine, or Darin's
engine. Even from city to city, and season to season those specs are going to change.
engine class I have little knowledge about.
The only thing I'm disputing is the direction of overlap toward a decreasing
value. Overlap is critical for any N/A engine. The amount of overlap doesn't
concern me.
I think many people here are getting too wound up on the exact figures, instead
of understanding the basics. I personally don't give a $hit if my overlap is
a degree off, or my IVO is not optimized. I had a quarter mile goal in mind
and I've achieved that goal. That makes me happy and the fact that I
can visualize and understand the effect of a later IVC or a tighter LSA using
similar lobes.
This discussion has gone from street engine to Prostock overnight and it's
totally confusing the conversation as far as I'm concerned. Nobody is going
to get the perfect cam numbers from this thread, or any other thread for that
fact. What's right for Giga's engine, is not right for your engine, or Darin's
engine. Even from city to city, and season to season those specs are going to change.