Rear end build help
 

Hello, currently seeking help with my rear end build. Want to know what would be a good gears setup for my car. I bought this car about 2 years ago and still rebuilding it. I'm mainly using this car for racing, going to buy another 3rd gen soon for my daily.

Engine Specs: (383 Stroker)

Cam - Voodoo Cam Duration 284/292, Lift 525/546
Crank - 400 Eagle Steel Crankshaft
Bore - .060 over
Heads - Vortec 67cc Chamber, 175cc Intake Runner
Tranny - 700r4

Tire Setup - 29 x10.5W

Re: Rear end build help
 

Gear it so that the engine is near its max HP RPM as it goes through the lights on whatever length track you're planning on running at.

That cam has about 240° of intake duration IIRC; should give peak HP at around 6200 in that size motor, probably around 425 HP. Work the HP/mph/weight equation to estimate trap speed, then plug that speed into a gear calculator with RPM & tire size to find the right gear, assuming 1:1 trans gear (3rd in a 700).

Re: Rear end build help
 

Not exactly. First, you need the loaded tire radius, which is less than half the advertised diameter.
Then, you need to know how much your torque converter slips at WOT; good converters slip about 400 RPM at WOT, I've had crappy ones slip as much as 1200.
Your actual trap speed will be 2-3 MPH more than what's shown on your timeslip, and there's a popular argument for trapping 500 RPM above your HP peak.
But if you were running 14 flats at 100, at 5000 RPM, then I'd gear for a calculated 4600 at a real 103. This is playing it safe, and is more streetable as well.
The math is easy: axle ratio x 336 x MPH / ( loaded radius x 2 )
so for example, 25.7 advertised = 24.9" tires, then 3.23 x 336 x 103 / 24.9 = 4489 = 4900. 3.42 x 336 x 103 / 24.9 = 4753 = 5150