Pro Stock cams

[Guest]

Just wondering if Darrin would give us a ballpark idea of the cam specs for a 500" Pro Stock motor. I'm aware that valve lift is better than 1", but just wondering how much duration is required to run at such high rpm. Does an IHRA Pro Stock motor have significantly more duration than a NHRA Pro Stock?

[Darin Morgan]

Just wondering if Darrin would give us a ballpark idea of the cam specs for a 500" Pro Stock motor. I'm aware that valve lift is better than 1", but just wondering how much duration is required to run at such high rpm. Does an IHRA Pro Stock motor have significantly more duration than a NHRA Pro Stock?

A typical Pro Stock camshaft is a 570 lobe 284 duration on the intake 560 lobe 304 duration on a 117. The rockers are 1.85 intake and 1.8 exhaust. Its no real super secret. That is about the average cam profile we use. We have bigger cams but they tend to hurt parts over 9800rpm. We will be going bigger in the near future. With the bigger core cams comes more lift. We are now at 1.050 to 1.060 gross lift with as little deflection as possible so the net lift is probably about .990 to .995. ( I am guessing) That does not tell the whole story. With lobe loft we actually get a dynamic 1.100 lift above 8500rpm.

The IHRA cams are 600+ lobes but I don't know what people are using in the duration department. I would expect it to be in the 290s at .050. They have REALLY wide LCs at or above 120. They can be much more aggressive on there lobe profiles due to the fact that they don't exceed 8500rpm.
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[maxracesoftware]

A typical Pro Stock camshaft is a 570 lobe 284 duration on the intake 560 lobe 304 duration on a 117. The rockers are 1.85 intake and 1.8 exhaust.

Darin , how close are you to .41 to .42 Lift/Diameter Ratio ??

.560 Lobe times 1.85 = 1.036 lift
.573 Lobe times 1.85 = 1.060 lift (1.100" Loft)

1.060 / .42 L/D = 2.524 OD intake valve ???
1.060 / .41 L/D = 2.585 OD intake valve ???

from Dyno testing a limited amount of various types of Race Engines,
the Data is trending towards .37 to .39 L/D Ratio for abrupt short turns
like 23 deg SBC heads -to- .41 to .42 L/D Ratio for large short turn modern raised runner heads with better valve axis -to- port axis

[Darin Morgan]

A typical Pro Stock camshaft is a 570 lobe 284 duration on the intake 560 lobe 304 duration on a 117. The rockers are 1.85 intake and 1.8 exhaust.

Darin , how close are you to .41 to .42 Lift/Diameter Ratio ??

.560 Lobe times 1.85 = 1.036 lift
.573 Lobe times 1.85 = 1.060 lift (1.100" Loft)

1.060 / .42 L/D = 2.524 OD intake valve ???
1.060 / .41 L/D = 2.585 OD intake valve ???

from Dyno testing a limited amount of various types of Race Engines,
the Data is trending towards .37 to .39 L/D Ratio for abrupt short turns
like 23 deg SBC heads -to- .41 to .42 L/D Ratio for large short turn modern raised runner heads with better valve axis -to- port axis

SSSHHHHHHHHHH! We don't want everyone to know that do we?
All kidding aside your research is right on track! I am glad to see others see the same thing I do. It helps to compare notes with others in the field because it validates our theories. The abrupt SSR heads will STOP running at about 8800rpm. Flows like crazy and will not run. How many time have we seen that? We got into the tall port, steep SSR routine about seven years ago and proved beyond any shadow of a doubt that it will not make power at high engine speeds with these cams. I think the velocity profile in the port right at the apex of the SSR exceeds.55mach localized velocity and everything STOPS. We had an engine with an SSR at 3 inches high and that engine would literally shut off at 8600 rpm. The higher the initial air speed the more critical the SSR becomes. I think that is why we are now seeing higher test pressures used to flow these heads. So we can mimic what the heck is going on.
I run no bigger than a 2.515 diameter valve 53.5% of the bore. If I go bigger it flows a little more but can never reach the same cfm/INsq so its efficiency drops and the power along with it. We are now at .417 L/D ratio gross and .437 L/D dynamic.

[Guest]

Darin, I'm wondering how the cams in your 358" PST motors compared to the current 500" cams. Were they similar, but with a little less lift?

[Darin Morgan]

Darin, I'm wondering how the cams in your 358" PST motors compared to the current 500" cams. Were they similar, but with a little less lift?

They where completely different than what we have today. That was years ago so camshaft lobe design has come a long way in just a year or two. I would approach those engines a little differently in regards to camshaft design and intake manifolding to take advantage of the 60mm cores. Its a case of ," if I only new then what I know now!" The cams intake lobes we had where .488 to .490 lobes at 279 to 280 duration @.050 on a 113 to 114 lC..
I would have a little shorter manifold with about the same size plenum and a .500 lobe at 282 on a 114.5 LC.and I would get on the Spin Tron at Comp Cams and work with them to utilize the loft at high engine speeds above 9500rpm. You really need to operate those engine between 9000 and 10500 rpm. I would not drop the engine below 8900rpm if at all possible. There is no reason a hard core effort could not make one of those trucks run 7.20s.

[Guest]

I'm interested to know if you ran a full 20 degrees more duration on the exhaust lobe with the truck motors too. Is that 20 degrees extra duration determined by the 60% exhaust to intake flow ratio? My current cam has only 6 degrees more on the exhaust even though the exhaust to intake flow ratio is 61%. I'm wondering if I need to look at adding more exhaust duration.

[Darin Morgan]

I'm interested to know if you ran a full 20 degrees more duration on the exhaust lobe with the truck motors too. Is that 20 degrees extra duration determined by the 60% exhaust to intake flow ratio? My current cam has only 6 degrees more on the exhaust even though the exhaust to intake flow ratio is 61%. I'm wondering if I need to look at adding more exhaust duration.

As the saying goes, You can get away with camming a mediocre exhaust port but you cant get away with camming a mediocre Intake port. In other words, you can make up for some deficiencies in the exhaust port flow with the camshaft. We all have moved the intake so far off the bore wall that the exhaust is now over in a hole against the cylinder wall. It does not flow as well as it could so we throw some more duration at it and speed up the opening ( get it into a high flow area quicker ) and everything works fine. If you tried that with an intake the engine would not respond or fall on its face.

I cant say for sure that your engine would respond to adding more duration to the exhaust. We really need to know more about the engine combination we are dealing with to make a recommendation one way or the other. Just adding duration isn't like a broad spectrum antibiotic that kills all ills. You need the right drug for the right disease.

[Guest]

Darin, let me give you a few more details. The motor is a 15 to 1 410 small block Chevy with GM 15 degree heads (402 on the intake and 255 on the exhaust w/no pipe), and a sheet metal intake with two fours. The cam is 286-292 on 113. I think the cam may be a bit too big because I only really want to run the motor to about 8300 or so.

The motor is in a 2800 lb 57 Chevy drag car with a Powerglide.

This cam was picked by the cam company I bought it from, but I'd really like to try somethng different for next year. Considering I have more intake duration than a 500 inch Pro Stocker, I'm guessing I have too much. Would you be able to give me a recommendation for a cam?

Thanks for your help,
John Wheatley

[Darin Morgan]

Darin, let me give you a few more details. The motor is a 15 to 1 410 small block Chevy with GM 15 degree heads (402 on the intake and 255 on the exhaust w/no pipe), and a sheet metal intake with two fours. The cam is 286-292 on 113. I think the cam may be a bit too big because I only really want to run the motor to about 8300 or so.

The motor is in a 2800 lb 57 Chevy drag car with a Powerglide.

This cam was picked by the cam company I bought it from, but I'd really like to try somethng different for next year. Considering I have more intake duration than a 500 inch Pro Stocker, I'm guessing I have too much. Would you be able to give me a recommendation for a cam?

Thanks for your help,
John Wheatley

You can call me any time at the shop and we can talk in depth about your combination and what we can do to make it work to your expectations.

[AR ENGR]

Darin,

What is the short answer on the super wide LSA? I'm not familiar with seeing numbers like 117 and 120. Most race cams that I see are in the 106 or 108 range. And it also seems like the more serious the motor, the tighter the LSA. But you guys have gone the other way.

[Darin Morgan]

Darin,

What is the short answer on the super wide LSA? I'm not familiar with seeing numbers like 117 and 120. Most race cams that I see are in the 106 or 108 range. And it also seems like the more serious the motor, the tighter the LSA. But you guys have gone the other way.

First I want to know what engine combination your dealing with when you say," Most race cams that I see are in the 106 or 108 range." What engines are you referring to?

[buddy rawls]

you can't group cams into applications based on durations and LSA. there is way more to it. there is a cylinder volumetric flow that is based on CID and rpm. then there is flow capability of the inlet and outlet paths with varying degrees of velocity and flow potential that are based on the cylinder volumetric flow. similarly to flowing a runner at a different static pressure (as an example) Also you will static compression that will play a tradeoff with cylinder pressure support versus total fillable cylinder volume.... etc

The PS motors and PST motors are going to be running enormous flow capability versus the cylinder volumetric flow. so for a given unit of time, you will be able to feed the cylinder with less duration. In addition, the highly efficient inlet flow and associated cylinder filling and VE is going to require the earlier exh events dependingon the total flow capabilityof exh path, and still maintain a nice overlap exchange with a lower angular number. lower overlap angle does not necessarily correlate to less overlap charge exchange. If the door is big, it does not have to be open as long. but there has to agreement between the valve events and flow potential to maintain good velocity and inertia.

In a superstock motor you see drastic differences. compare a SS motor to a PST motor, looking at all the parameters and you can see what is happening. the restricted inlet capability is going to really require careful selection of the IO/IC to work in conjunction with head running near its velocity/flow cut-off, without compromising the cylinder fill with too long of seat timing activity. Likewise the overall lower cylinder fill potential will respond much more favorable to the later exhaust events. So you will see some the more restricted set-ups really bring the LSA in narrow, even to the 100-104 range at times.

In my 'real quick' calcs the 15:1, 410CID cam did not seem real out of whack for the flow potential (I assumed a 2" exh primaryOD). Depending on the particular powerband aspects as well as the lower lift E/I flows and the total inlet path flows, it may be changed around a bit.

One thing I wanted to add, is that alot of people think the valve event derivation process varies from application to application. It doesn't and shouldn't. the goal is the same, its just the numbers may look different. It is entirely possible to use the same EXACT process and math for a street emissons performance as for pro-stock motor and 4cyl off-road motor. the cams may look astronomically different but the process can be identical.

[Jay Allen]

The motor is a 15 to 1 410 small block Chevy with GM 15 degree heads (402 on the intake and 255 on the exhaust w/no pipe), and a sheet metal intake with two fours. The cam is 286-292 on 113. I think the cam may be a bit too big because I only really want to run the motor to about 8300. The motor is in a 2800 lb 57 Chevy drag car with a Powerglide.

It is my opinion that cam companies typically choose camshafts that are too big at .050" on the intake side. It is my belief that camshafts that are small(er) at .050 and a little more lobe area by the lift will make more average power. This is ecspecially true in an automatic situation where TQ is your friend.

It would be nice to know how big the cylinder head is this example. On an engine that has an average piston speed of 5187.5 ft/min, there had better be a fairly large cross sectionally head on this thing to feed it!

Thanks!

[Guest]

Jay,

So is it safe to say that a cam that is bigger at .050 with the same lobe area and less rocker arm would be more "Peakey" and require a 5 speed to work. (Like a Pro Stock Cam?!?!?!?!?!)