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Cam design basics ?

General engine tech -- Drag Racing to Circle Track

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CamKing
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Re: Cam design basics ?

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ptuomov wrote:CamKing -- Thanks a lot, that's very useful and detailed info. Do I understand correctly M product code means mechanical? Would these run well on a hydraulic lifter? Would the H74500Ex that you listed in your Cayenne DP (Diesel Power?) cam post work, it looks similar to that profile? Or am I just assuming untrue things about your product coding system?
Sorry, that should be an 'H74500EX", not "M74500EX", and it is a Hydraulic lifter profile.

And MadBill was right, the DP is for Daytona Prototype, and Porsche did not like getting beat by their own engine.
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Re: Cam design basics ?

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Interesting. Do you happen to remember what the base circle diameter is for those Porsche Cayenne cams? Also, could those profiles be run on a 35mm hydraulic tappet?
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Re: Cam design basics ?

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op
the isky catalog does a good job in explaining stuff... :)
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Re: Cam design basics ?

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Ok so Boxter and Cayanne have 33mm lifters so these should fit on a 35mm lifter just fine.
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Re: Cam design basics ?

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ptuomov wrote:Interesting. Do you happen to remember what the base circle diameter is for those Porsche Cayenne cams? Also, could those profiles be run on a 35mm hydraulic tappet?
Yes, they'll work on a 35mm hyd tappet.
Base Circle on the Cayenne cams was 1.440"
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Re: Cam design basics ?

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Bringing this one back from the dead.

I heard Mark Cronquist of JGR mention today about closing the intake valve "early"* on restrictor engines / limited compression engines to build cylinder pressure, but he has learned with the less rules JGR Baja truck engines that you can close it too early.

I can imagine what is happening here, but anyone with experience elaborate on this? Mike?

*early is relative to what you would one would think the engine wants for the rpm, I am assuming.
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Re: Cam design basics ?

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hoffman900 wrote: Thu Jan 13, 2022 10:02 pm Bringing this one back from the dead.

I heard Mark Cronquist of JGR mention today about closing the intake valve "early"* on restrictor engines / limited compression engines to build cylinder pressure, but he has learned with the less rules JGR Baja truck engines that you can close it too early.

I can imagine what is happening here, but anyone with experience elaborate on this? Mike?

*early is relative to what you would one would think the engine wants for the rpm, I am assuming.

I want to go back and watch that part again. It was interesting for sure. I’d like to know how he defines limited compression, as in a number or a relatively low CR for the cam timing you need. If that makes sense.
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Re: Cam design basics ?

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ClassAct wrote: Thu Jan 13, 2022 10:24 pm
hoffman900 wrote: Thu Jan 13, 2022 10:02 pm Bringing this one back from the dead.

I heard Mark Cronquist of JGR mention today about closing the intake valve "early"* on restrictor engines / limited compression engines to build cylinder pressure, but he has learned with the less rules JGR Baja truck engines that you can close it too early.

I can imagine what is happening here, but anyone with experience elaborate on this? Mike?

*early is relative to what you would one would think the engine wants for the rpm, I am assuming.

I want to go back and watch that part again. It was interesting for sure. I’d like to know how he defines limited compression, as in a number or a relatively low CR for the cam timing you need. If that makes sense.
Yeah, it's all relative. He stated it started with the 12:1 rule in NASCAR, and then in relation to the restrictor plate engines, which obviously were well above 12:1 before the compression rule.

Hopefully Billy Godbold touches on it tomorrow.
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Re: Cam design basics ?

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hoffman900 wrote: Thu Jan 13, 2022 10:02 pm Bringing this one back from the dead.

I heard Mark Cronquist of JGR mention today about closing the intake valve "early"* on restrictor engines / limited compression engines to build cylinder pressure, but he has learned with the less rules JGR Baja truck engines that you can close it too early.

I can imagine what is happening here, but anyone with experience elaborate on this? Mike?

*early is relative to what you would one would think the engine wants for the rpm, I am assuming.
Welcome to the 90's :lol:

Back in the late 80's and 90's we had a lot of limited compression classes in circle track racing. Many in the 9-9.5:1.
To increase power, we needed to increase cylinder pressure. By increasing the lift, reducing the duration, and closing the intake valve sooner, we could increase the charge velocity into the cylinder, and increase the ram air effect. This increased the amount of mass into the cylinder, increasing the cylinder pressure, and increasing the power. It was very common for these engines to be running a 98-100 Intake Centerline.

We took what we learned from the limited compression engines, and used in in the restricted carb and restrictor plate engines. When the restricted inlet engine is above the point where the carb or restrictor plate starts restricting, the mass of the intake charge is reduced, and that reduces the cylinder pressure, so the higher lift, shorter duration, and earlier intake closing helped the power.
The issue was below the point the carb or restrictor plate started restricting. Below that point, the engine is seeing no reduction in mass of the intake charge. In these lower RPM's that early intake closing is way too early, and the cylinder pressure is too high.
Look at it this way, at high RPM's the engine thought it was running in Denver Colorado, but at low RPM's, it thought it was running in San Diego. We had to come up with a compromise for cam timing.
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Re: Cam design basics ?

Post by hoffman900 »

Thanks, Mike. I totally understand what a restrictor does to choke flow / mass flow.

I think where I am most curious about is how it relates to engines where you hold compression lower for reasons related to efficiency. Take an old hemi chamber for example, something like a Norton, old Chrysler Hemi, Toyota 2TC's, and the like. A dome that isn't going to trash the compression process might mean 10-11:1 compression. Knowing that, would you purposely close the intake sooner for that application if I told you fuel octane wasn't an issue (ie: not rules limited, etc.)?

Like where is the tradeoff in trashing combustion efficiency with high static compression ratios and their corresponding domes vs. gaining it back with an earlier intake closing? With NASCAR being held to 12:1, they obviously had to pursue other avenues to get cylinder pressure, and I think that's where Mark was coming from.
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Re: Cam design basics ?

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That's exactly what we did with the classes that were restricted to 9-9.5:1 compression.
there were a lot of restricted compression classes in the late 80's, Modifieds, Asphalt Latemodels, Winston West stock cars, and others.
Besides the compression limit, these were engines that had been well developed (358ci SBC, 23degree aluminum heads, single plane manifold, headers, etc). Everyone in the industry had a lot of experience with every aspect of these engines, except the compression limit.
We started with what worked in a 13:1 version of the same engine. We kept shortening up the duration, and getting the area back by increasing the lift, and closing the intake valve earlier and earlier.
this increased the velocity of the intake charge, increasing the ram-air effect, which increased the mass trapped in the cylinder, and that increased the compression pressure and heat. On average, we were reducing the duration by about 8 degrees, and advancing the intake centerline by about 4 degrees, so we would have about the same intake opening point, but be closing the intake about 8 degrees sooner.
What we found when we kept going farther in this direction, you reach a point where you are no longer increasing the amount of mass being trapped in the cylinder, yet the temp keeps climbing. The higher heat required us to adjust the fuel and spark, and those adjustments would hurt the power.
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Re: Cam design basics ?

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It's like everything else. There's always diminishing returns.
I tell my customers that run Methanol, to run as much compression as they can get, and in practical cases, that's correct, but even that has a limit.
No matter how good the fuel is, you will reach a point where the added power made by the increase in compression, is less then the power required to compress that added compression.
Everything has it's limits.
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Re: Cam design basics ?

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CamKing wrote: Fri Jan 14, 2022 1:08 pm It's like everything else. There's always diminishing returns.
I tell my customers that run Methanol, to run as much compression as they can get, and in practical cases, that's correct, but even that has a limit.
No matter how good the fuel is, you will reach a point where the added power made by the increase in compression, is less then the power required to compress that added compression.
Everything has it's limits.
Thanks, Mike. These are the answers I was hoping to get.

Since you were there, what did Honda first mess up with their foray into Indy Cars in the mid 1990s? They relied on their V6 turbo and NA F1 experience and whiffed it.
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Re: Cam design basics ?

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hoffman900 wrote: Fri Jan 14, 2022 1:15 pm
Since you were there, what did Honda first mess up with their foray into Indy Cars in the mid 1990s?
Are you talking about the Judd-Honda that debuted in 1988 ?
That engine was designed and Built by Judd, and Honda just put their name on it.
I never looked inside of one, but it was a new engine, trying to run against engines that had been running in IndyCar for over a decade(the Cosworth V8, and the Ilmor that was almost an exact copy of the Cosworth), and were well developed by 1988. Besides the fact that the chassis were all designed around the Cosworth/Ilmor engines, The guys running the series(CART) were all connected with Cosworth or Ilmor.
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Re: Cam design basics ?

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CamKing wrote: Fri Jan 14, 2022 1:48 pm
hoffman900 wrote: Fri Jan 14, 2022 1:15 pm
Since you were there, what did Honda first mess up with their foray into Indy Cars in the mid 1990s?
Are you talking about the Judd-Honda that debuted in 1988 ?
That engine was designed and Built by Judd, and Honda just put their name on it.
I never looked inside of one, but it was a new engine, trying to run against engines that had been running in IndyCar for over a decade(the Cosworth V8, and the Ilmor that was almost an exact copy of the Cosworth), and were well developed by 1988. Besides the fact that the chassis were all designed around the Cosworth/Ilmor engines, The guys running the series(CART) were all connected with Cosworth or Ilmor.
No, the 1994 engine when Rahal had to buy a Ilmor-Chevy Penske car to qualify for the Indy 500.
-Bob
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