[Tim Corcoran]

This is an interesting video and there is a part two that is good also

https://youtu.be/JPAeepqrY-0

[chuckies76ta]

Thanks for posting Tim. Very interesting.

https://www.youtube.com/watch?v=oBGkWGuwXLU

[Steve C.]

Regarding his point stating there is not really much gain when a port is maxed out in cfm air flow no matter how far you continue to open the valve it cannot flow any more air.

Regarding that, if interested there is this tid bit to explore that is published by David Vizard:

VALVE LIFT.
"A 2-valve cylinder head typically continues to flow more air up to lift values equal to as much as 0.35-0.4 times the valve diameter. The reason for this is that there is a flow pattern transition period that takes place at a lift value of about 0.25 of the valve's diameter. When this point is passed, if the port has been modified to support flow in this lift region, the valve efficiency actually starts to increase. This is the reason why a 2-valve engine responds to high lift."
"If you want to build a street motor with the most power without a sacrifice of idle and low speed qualities, then lift is the most important factor to maximize, not duration. The best street cams are those that seek to maximize lift while only adding a minimal amount of duration."

And another tid bit to explore, in part from the video....

"... the crank shaft has to overcome the resistance that the cam is putting on it so in other words the cam is a parasitic draw it takes horsepower to actuate the cams it also takes horsepower to compress these springs..."

Does this info below relate ?

Common Misconception:
Many people mistakenly think that using higher seat pressures causes a reduction in the horsepower delivered to the flywheel because higher seat pressures (and also higher spring rates required for high performance) require horsepower to compress the springs. This thinking is simply incomplete! For every valve that is opening and its valve spring being compressed, another valve is closing and its valve spring is expanding. This expansion returns the energy to the valve train and the engine. This results in a net power loss of "0" hp. Many engineering texts refer to this as the "regenerative characteristic" of the valve train. Recent tests at Crane have shown no horsepower loss on a hydraulic roller equipped engine when changing the seat pressure from 135# to 165#. Power actually improved significantly at top end, probably due to better control of the relatively heavy valves in the engine.
Source: Crane Cams


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[Dragncar]

Its a good video. A detailed video mostly for newbies.
There is stuff there (Vizard) even though he says there is not.
But he does use a flow sheet to pick a cam . I think thats a good idea.
The stuff about valve springs and them being a straight parasitic drag ? He did not mention the other side of the lobe giving some back.

[Tim Corcoran]

I noticed the same thing about Spring pressure that info is not correct. Even so it is a good video with some good entry level info. His second video on the same subject is also very good and a little more advanced. On that video he talked a lot about exhaust scavenging but least out an important aspect of it, specifically how the exhaust gas during overlap will actually pull in the intake charge during overlap. This is how a naturally aspirated engine can exceed 100% VE

[Steve C.]

Agree, nice videos.

In the first video he mentions a way to figure out how much horsepower you can get potentially from the cylinder heads and a SuperFlow formula involving their CFM air flow.
Appropriately he also stated for his build that parts weren't just thrown together to meet the horsepower goal.

Related to this, Air Flow Research also uses a similar formula as in the video. However it predicts a normally aspirated engine's horsepower potential based on "intake-system airflow".
But note, and important, according to Air Flow Research they state it is based on the net cfm airflow delivered at the valve thru the carb, intake manifold and cylinder head.
Not the cylinder head cfm flow itself.

There are some caveats involved, and as alluded to in the video, and also relates to not just throwing parts together. Air Flow Research points out that actually reaching the predicted power level requires the engine to have the right compression, the right cam, a tuned exhaust, and a nonrestrictive carb and intake manifold. AFRs view is the combined lift generated by the cam lobe and rocker arm should equal the observed lift on the flow bench needed to achieve the desired intake port flow, plus a good exhaust port flow. Etc, etc.


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[PAUL K]

Originally Posted by Tim Corcoran

he talked a lot about exhaust scavenging but least out an important aspect of it, specifically how the exhaust gas during overlap will actually pull in the intake charge during overlap. This is how a naturally aspirated engine can exceed 100% VE

I haven't watched the video but I've been preaching that for years on here. I usually get flamed any time I mention it in the "street" section.

[PAUL K]

Originally Posted by Dragncar

Its a good video. A detailed video mostly for newbies.
There is stuff there (Vizard) even though he says there is not.
But he does use a flow sheet to pick a cam . I think thats a good idea.
The stuff about valve springs and them being a straight parasitic drag ? He did not mention the other side of the lobe giving some back.

One should use all info available to spec a cam. Knowledge is power.

As far as spring pressures go I remember great debates on this Website in regards to that subject. I think it was finally decided as one spring was opening and fighting the spring pressures another was being helped by the pressure as it closed. So they cancelled each other out regardless how much pressure was used.... I
always thought that would mean an assembled engine would spin by itself...that has yet to happen.

I'm sure Dan Whitmore told you about the gains in power he found by reducing spring pressures.

[Steve C.]

Horsepower to compress the springs. That was addressed in my post #3


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[Dragncar]

Originally Posted by PAUL K

One should use all info available to spec a cam. Knowledge is power.

As far as spring pressures go I remember great debates on this Website in regards to that subject. I think it was finally decided as one spring was opening and fighting the spring pressures another was being helped by the pressure as it closed. So they cancelled each other out regardless how much pressure was used.... I
always thought that would mean an assembled engine would spin by itself...that has yet to happen.

I'm sure Dan Whitmore told you about the gains in power he found by reducing spring pressures.

Yes he did. He told me about some Pontiac builders who put a 8500RPM spring for a engine that is done by 6500RPM. Some shop in "Ohio".
He said all that extra spring pressure contributed to breaking lifter bores in a Pontiac too.
I miss that guy, I used to bounce a lot of stuff off him and always got a good answer.
He told me about you. Not by name but a younger guy looking to get into the business he helped out, had to be you.
The valve spring parasitic loss deal. I am sure heavy spring pressure does take more power to turn the engine over. But you get something back on the other side of the lobe. I doubt its 1 to 1. Has to be some formula-ratio.

[Steve C.]

Three links to explore.....

How much 'parasitic load' does a camshaft represent?

https://cr4.globalspec.com/thread/25...haft-represent

Valve Spring Power Consumption

https://www.eng-tips.com/viewthread.cfm?qid=236426

Calculate Torque Required to Turn Cam

https://www.reddit.com/r/Engineering...d_to_turn_cam/

" I was taught that the only power taken away from an engine due to the installation of heavier valve springs (very little) was due to extra friction/heat created. Valves being pushed down, and others returning should cancel themselves out..
Plus flat tappet and roller cams exist if that makes any difference in the power required. I'm a CS student so.. I'm not sure how specific calculations would have to be."

( Information provided in this post does not represent any endorsement and is offered for general interest only )


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[jhein]

Seems like it would be pretty easy to measure the amount of torque required to turn the cam with the valvetrain fully assembled. Also seems like it's possible that it could be slightly different in a running engine with the the gasses flowing, compressing, combusting etc. whatever forces that may exert on the valves.

[chuckies76ta]

Case in point. Take the spark plugs out and spin the engine over. It spins pretty easily. So there can't be that much resistance to the valve springs.

[PAUL K]

Originally Posted by jhein

Seems like it would be pretty easy to measure the amount of torque required to turn the cam with the valvetrain fully assembled. Also seems like it's possible that it could be slightly different in a running engine with the the gasses flowing, compressing, combusting etc. whatever forces that may exert on the valves.

Originally Posted by chuckies76ta

Case in point. Take the spark plugs out and spin the engine over. It spins pretty easily. So there can't be that much resistance to the valve springs.

Fwiw engines with stiff springs are noticeably harder to turn over by hand. The first engine I assembled that used 1100 pound springs (380 closed) seemed like it locked up after installing the first rocker arm. I was thinking the valve was hitting the piston. After the rest of the rocker arms were installed that engine turned over easier. So there is some merit with the theory the closing springs help the opening springs fight the spring pressures.

However I have yet to see one keep spinning on its own.

[Stan Weiss]

I am sure that someone on a spin tron has measured the difference in HP needed to rotate an engine at lets say 7500 RPM with different spring rates. I just have not seen that data.

Stan

[grivera]

Great video. While not the point of the video, he mentioned was a 20% hp loss from flywheel to tires. Paul Carter pointed out using a percentage is flawed logic as it would mean an 500 hp engine would lose 100 vs a 250 hp engine losing 50 hp.

[Dragncar]

The part I am wondering about is where he takes the total potential HP on a 338 cfm head and uses the 91% of the exhaust flow and only comes up with 639 horsepower. (703 x 91%)
No Pontiac head I know of has a 91% intake/exhaust ratio so the typical Pontiac head is going to be worse.
But we have all seen 340 cfm Pontiac heads making far more than 640 horsepower.
Am I missing something ?

[Tim Corcoran]

Originally Posted by Dragncar

The part I am wondering about is where he takes the total potential HP on a 338 cfm head and uses the 91% of the exhaust flow and only comes up with 639 horsepower. (703 x 91%)
No Pontiac head I know of has a 91% intake/exhaust ratio so the typical Pontiac head is going to be worse.
But we have all seen 340 cfm Pontiac heads making far more than 640 horsepower.
Am I missing something ?

I was thinking the same thing because the ratio between intake and exhaust flow on a Pontiac engine is not great even on a ported E-head with upgraded 1.77 exhaust valves, yet they still make pretty good power so I would say the data he provided in the video was flawed or at least exaggerated with regards to HP limitations on exhaust to intake flow percentage. Even so I didn't agree with everything presented in the video but still think some good info was presented and it was an interesting presentation on both videos. It appears most of his experience was related to LS, SBC and BBC engines. He also discussed the long debated short rod long rod subject. Smokey Yunick said to install the longest rod that can fit into the engine, what he didn't say the longer rod will give you more power. Pro Stock cars don't have an ideal rod to stroke ratio but make massive power per C.I. So I believe the real advantage to a long rod is reduced cylinder wall loading which will give some longevity to the bore and less stress on the rotating assembly. Some say cam selection is critical to a long rod vs a short rod engine because a longer rod will have he piston dwell longer at TDC than a short rod. There is a tradeoff at some point as a short rod weighs less and a long rod has less cylinder wall loading. For a bracket car a longer rod is my preference.

[Formulajones]

Originally Posted by Tim Corcoran

On that video he talked a lot about exhaust scavenging but least out an important aspect of it, specifically how the exhaust gas during overlap will actually pull in the intake charge during overlap. This is how a naturally aspirated engine can exceed 100% VE

Ive mentioned this before. Pulling in the intake charge during the exhaust stroke also has the affect of cooling the next cycle, the compression stroke. This helps ward off detonation. The more you advance the camshaft the more the intake valve is open at TDC on the exhaust cycle. Paul C explained it to me that he likes to see the intake valve open around .030-.040" at TDC on the exhaust stroke. This isnt always doable depending on the cam LSA. Wider LSA makes this harder to accomplish. On wide 112-114 LSA cams I can usually reach about .020-.025"

[Steve C.]

I agree with Tim's post regarding the long rod issue.

I'm of the opinion the increased popularity of the longer rod in a Pontiac situation came about with Jim Butler's involvement probably 30 or more years ago with his collaboration with the Eagle crank deal. And related, within his articles in Pontiac Enthusiast magazine back then he mentions his use of the 4.250 stroke crank and 6.8 rods, along with his custom JBP Ross pistons. It increases the displacement of the 455 engine. At the same time, the better rod angle, the improved rod-to-stroke ratio of 1.6:1, and the raised pin location in these custom pistons relieve the stress on the block. The higher pin pushes up on the piston instead of out on the skirt and results in less friction.

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