I understand the need to balance HP with torque and RPM. Obviously you don't shift at 4,500 just because torque starts to decline after then. I just returned from Watkins Glen where I drove a friends STi that has a close-ratio six speed (Spec C fifth and sixth). It was running 245 /18 tires and pretty well max'd out the RPMs on the back straight. I could see that being a problem on tracks with longer straights without a higher RPM range. It's also a problem in "the boot" between 7 and 9, where I have to feather the throttle a little if I run out of revs.
My STi engine is set for a 7,200 RPM limit though it should survive 9K (so says Manley about my 26180 spring kit). That would have been pointless with the old, smaller, stock turbo since it starts running out of breath by 6,500.
From my research I was surprised to find that mildly tuned stock motors, in the 300 WHP range, did better than many modified motors at making torque early and had less torque drop-off as they approached 6,500 RPMs. This makes me wonder about what kind of mods really work. I think anything to make the engine more efficient will help. By this I mean improving head flow and reducing back-pressure after the turbo, as examples. I'm not so sure about changing cams when the DAVCS cams seem to perform so well up to the mid 350's.
This is EFI Logic's race motor for ST2 from 2010. It has 272 cams and possibly a ATP30R turbo. More power than we need...
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