Originally Posted by 1BIGJIM

(1) With this combination would it be worth the time to have a custom cam made for my application? Will I see that much of gain in HP?

(3) Any other suggestions would be great.

Stroked 496 MarkIV
9:5: Compression Ratio
Edelbrock Marine Heads, Oval , 110CC
Imco Exhaust
RPM AirGap Intake
Barry Grant 750DP
Currently Comp Cam Extreme Marine 270
224/234 @.050 and .550 lift

I only want to spin this setup to 5,300 RPMS Max

Originally Posted by 1BIGJIM

This thread got interesting.

Any suggestions for my application

Originally Posted by JCPERF

Call up Crane and get a 525HP Mercury cam.It runs good in alot of combos.They make the cams for Mercury

Originally Posted by 1BIGJIM

This thread got interesting.

Any suggestions for my application

Originally Posted by SB

I believe I understand where you are coming from, but my thinking is that if you are going to start releasing comb pressure why do it slowly - ie: longer seat to .050" ? You'll get some pressure release but not a whole lot of flow.

If we want max exhaust flow, why wouldn't we get the exh valve to open faster ? Less psi to help evacuate the exhaust at 'flowing lifts' doesn't seem as favorable to me as more psi at 'flowing lifts.'

The pressure decay of a low compression engine (piston going down during power stroke) isn't that fast and the psi itself isn't all that high - compared to higher compression engine.

So, if we decide on this 10 degree split is best for this certain engine, why wouldn't we open it then and get it open as fast as possible to use the combustion pressure to our adavantage ?

Again, the piston is going down here, therefore we are using only pressure differences to evacuate the cylinder.

As we know, the more gases left in cylinder the more pumping losses we'll see as piston then comes up and has to force rest of exhaust out.

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I've studied a lot of wide exhaust seat durations this past year and a bunch of motors + applications will like up to 10 degree seat and at .050" (not all of course - many like lower)spread but I've very rarely seen any respond to say 13,14, or etc spread. Reading on the 12-16 spreads with very high compression and/or nitrous and/or big boost SC engines, has revealed this still causes some power loss (not that much because of higher comb psi - psi decay quicker because of high psi) but is to releive the parts eating heat that would cause problems if exh valve was closed a little longer.

BTW: Studied means I'm still looking at this stuff, and thus why my questions. It's pretty interesting and a pretty deep area of information. Therefore, I'm not poking but just trying to pick your brain - as I'm doing with many others on this subject - to see as many explanations / theories / experiences on this subject. Always more than one way to skin a cat. Poor ol' cat. LOL.