Thread: Picked up some GT 40 P heads

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Originally Posted by DennyW

The only thing I see with going over your cam specs, is you will have 2= Over Drive gears... 4th gear for 45-50 mph, and 5th gear for 80+ mph...

Do you mean that with the 3.0 rear gears or the 3.50 rear gears?

Here are some calculations based on my 5th gear at .68:

R&P ratio 70mph 5th gear .68 RPMs
3.0 1714
3.50 1999
3.89 2222
4.11 2348

Since you said I'd have 2 overdrives, here are the numbers for 4th gear at 1.0:

R&Pratio 70mph 4th gear 1.0 RPMs
3.0 2520
3.50 2940
3.89 3268
4.11 3452



I may end up with a 29" tire which would change these numbers a little but not too much.

This chart didn't post the way I intended but I think you guys can figure it out. It's all figured at 70mph with the different rear gear ratios with a 28" tire. The same is applied to both 4th & 5th gear.