T56 into a classic

[dan468]

Originally Posted by capev86

nice thing about this trans is there are 2 pair of overdrive ratios available (and corresponding first gear ratios). you can have hot rod performance, big rig power AND drive smooth on the highway and get awesome (for a truck) gas mileage with a proper 6 speed. i want to put one of these behind a hot rodded 292 in an early 50's chevy 1 ton panel truck done up to look completely stock right down to the wheels (but with a modern chevy 8 lug chassis with IFS, sway bars and 4 wheel disc....some day)

.8 (5th) / .62 (6th) that would be great behind a 3.42, 3.73, 4.10, 4.11, etc

4.10 x .62 = 2.54 overall

.7 (5th) / .52 (6th) that would be awesome behind a 4.56, 4.57, 5.13, etc

4.57 x .52 = 2.38
5.13 x .52 = 2.67
6.13 x .52 = 3.19 (think rock crawler or stump puller with highway ability)

in comparison, a stock 700r4 in OD

3.07 x .7 = 2.15
3.73 x .7 = 2.61

obviously somewhere between 2.50 and 3.00 is good for mild highway driving (60-70mph). you can see why the 3.07 is a terrible choice in a truck.....it has to work too hard to make overdrive worthwile and so gas mileage is no better than with a more aggressive gear even if the rpms are lower. with OD and a 3.73 you get the best of both worlds! you obviously want to stay well above 2.00 unless you have a turbo diesel truck with a banks kit or other serious mods (tons of torque). tire height and chassis tonnage/primary use and driving pattern will also determine what you want to run. i love my funky 3 on the tree in my 72 burb 3/4 ton 2wd, but if it had been a floor shifter, i'd rip it out and put one of these bad boys in when i get my 406sbc in my truck!

so 3.73 is the best route?