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Well, Ive read some on this subject and always found different information.

Whats your conclusion, does a long dur cam affect cylinderpressure or is this just BS?

Thanks
Matt
 

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Got to check the intake closing point. After checking out comp cams high energy series vs the magnum series, there is quite a bit of difference between when the valves close on cams with the same lift. The magnum series cams allows you to run more compression because of the late valve closing.
At lease thats what comp cam told me, and why doesn't cam manufactures show the closing degree on their advertisements if it is so important in selecting a cam?
 

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You can't bleed off pressure you don't have, and once the valve is closed, it shouldn't leak. The old John Deere tractors have a bleed-off valve at the top of the cylinder to bleed off enough cranking pressure to allow a man to start the engine by manually rotating the flywheel.
 

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I've been working the graveyard shift (11pm to 7am) doing some vehicle testing/mileage accumulation (500 miles a shift). I'm a little groggy. I think I've commented on this before but the explanation of long duration or overlap "bleeding off" compression is not a good explanation of the interaction between cam timing and pressure.

As far as the "why don't the manufacturers..." comment, this is another bit faulty logic reasoning.
 

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What PW said.

I agree with Paul.Also note some cam companys will advertise their cam timing / duration at .020 , but the recomended valve lash will be .024:shh:
So you must calculate your ACTUAL running timing at .024;) and factor this into your comparisons of other cams.:D

IMHO it's best to compare VALVE timing at a half a thou with running lash in.This is what the running engine see's.Lift rate and lift under the curve is another area to be considered,,but IMO the true valve timing is when the valve just sets down or just breaks it's seal.There's alot of performance lost or gained at lift's under .020.

WP:) RED67:chev:
 
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