If you are only interested in 0 to 60 speed, then pick a ratio that puts you at 60mph with no gear change or just one gear change and puts you at the rpm of peak hp plus about 5% .
To find this ratio, you will need to know the exact tire circumference, and the aforementioned rpm of peak horsepower.If you dont have a dynochart, you will need one of those in-car accelerometers,like the Dynorad or the G-tec.Any other way could be a shot in the dark.If you have to shift more than once before you hit 60,your car may/will be slower than if you coulda hung in there. I like a one-gear 0 to 60, but it takes a pretty good motor to get there quick, and even more $ in the suspension.
I believe you will need 2 gears,with your combo.
Heres the math; (RPM x Tire circumference)/(1056 x Rear gear x Trans lowgear)
rewriting it to solve for gear,we get;
Rear gear =1/(mph x 1056 x trans low)/(rpm x tc)
So lets say you have 26 inch tires, an auto trans with ratios of 2.45-1.45-1.00, and that your engine peaks at 5000 rpm. Then;
Rear gear = 1/(60 x 1056 x 1.45)/ {(5000 + 5%) x (26 x 3.1416)}
and RG = 1/91872/(5250 x 81.7)
and RG = 1/.2142 =4.67
The closest ratio is a 4.56, which will require reving to 5128 @ zero convertor-slip. Bingo
Doing the same math with a one-gear(2.45 low) 0-60 requires a 2.73 RG
Obviously other ratios will work. But every other ratio will require a sub-optimum gearshift that typically costs a quarter or more seconds in a stock box, during which time the power is burning clutches.
Also obviously; if your engine is peaking at a later rpm, the gear will need to be larger, unless you use first gear. For a 5600 peak, the optimum numbers are 5.13 for 2-gear and 2.94 for a 1 gear.
If you just wanna have fun, stick whatever in there, bigger than about 3.55( which will put you at 4000/60/2nd). 3.91s get 4400/60/2nd
Aint math fun?
