[25stevem]

You can’t just look at the exh to intake ratio, the level of cylinder pressure the motor will make and how fast from BDC the piston gets to its fastest acceleration point are all factors.

Low compression motors leave far more unused gasses ( think of heat that can no longer be used to drive the piston ) in the cylinder at the time the exh valve opens and this added amount of unused gas requires more time to get out of the motor.

This is one of the main reasons that even though low compression motors make less power then a similar high compression motor, they tend to run hotter.

[Steve C.]

Regarding the exhaust -to -intake ratio I would suspect the entire exhaust system in use from the cylinder heads to the tail pipes comes into play.

Example, a 2-1/2" system vs a 3" system, type of mufflers, etc.


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[Skip Fix]

Originally Posted by 25stevem

You can’t just look at the exh to intake ratio, the level of cylinder pressure the motor will make and how fast from BDC the piston gets to its fastest acceleration point are all factors.

Yes and no. Like Steve C said it is the whole exhaust and intake packages. But it all STARTS at the head. If you can get way more out the exhaust port to tailpipes why do you need more exhaust duration. Too much overlap and big exhaust can kill velocity and scavenging out. You have an intake deficiency! So working on getting more intake flow in vs exhaust out is what you need. 4 different cams, 2 sets of headers and a couple of different exhaust systems om my NMCA RAIV I played that game.

Talks with John Schloe n his RAIV Stocker and John Angeles on his SS RAIV also.