Originally Posted by
Roadknee
When you consider the stock Vortec 350 is some 255 hp at 4,400 at the flywheel this is a very impressive build. It's making over 255 at the wheels at 4,400 and some 320 hp peak.
For what it's worth, the 4L80E and 14 bolt probably won't show a drastic reduction on the chassis dyno compared to the 4L60E an 10 bolt rear. The acceleration rates on a chassis dyno are relatively low so the additional hp required to accelerate the higher mass is relatively low as well. As acceleration rates grow, the difference between the two would become more apparent. Even so, I recall a HP TV episode where they compared a Mopar drag car at the track with a 8-3/4" rear and a Dana 60. The D60 is a much larger and heavier unit, but the 1/4 mile time was basically unchanged.
I have a header design program called Pipemax that also does a pretty good job of estimating torque and hp given some basic engine parameters. It predicts 255 hp and 340 ft-lbs for the stock vortec assuming 95% peak VE, which I think is about right for these motors. Your motor peaks on the chassis dyno at around 5,600, and would peak a few hundred rpm higher on an engine dyno. The exhaust manifolds are the real bottleneck and are likely limiting VE to something under 100%. Assuming a 5,800 rpm engine hp peak and 98% VE, Pipemax predicts 380 peak hp and 380 peak ft-lbs. Your headers might increase VE to 102%, which is what my AFR headed 383 with equal length tuned headers makes. Pipemax predicts 400 peak hp and 400 ft-lbs. Pipemax also recommends intake and exhaust valve lift of 0.564" intake and 0.540" exhaust (preferred) and 0.500" intake and exhaust (minimum) to prevent choke. Depending on your valve lift, you can potentially find some gains there as well.
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