IVC & manifold design effect on RPM
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TECH Apprentice
Joined: Sep 2005
Posts: 334
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IVC & manifold design effect on RPM The production style long runner LS cathedral port intake manifolds seem tuned to deliver peak torque ~4800rpm and peak hp ~6200rpm. We see a lot of camshafts with very late @ .050" IVC events (50*+ ABDC) that seem to help hold the power from falling off after the manifold induced peak. These late IVC events seem effective at stretching the useable powerband to 7000 rpm or higher. However, even relatively mild cams with IVC events 10* earlier pull strongly to ~6500 rpm. It seems like you need to "over-cam" the motor quite a bit to get past the intake design. So, if you get rid of the long runner manifold and go with a single plane 4bbl style, or a shorter runner like the new Edlebrock Pro-Flow XT, wouldn't it make sense that your cam choice should close the intake valve earlier to achieve the same rpm range? I would think that IVCs in the mid to late 40's ABDC should be able to peak at 6500+, and pull to 7000+, if not constrained by the intake runner design. Does that seem reasonable?
