Thread: Changing internal gearing? (not final drive)

4L80E ratios are
1st-2.48
2nd-1.48
3rd-1.00
4th-.75

4T80E ratios are
1st-2.96
2nd-1.63
3rd-1.00
4th-.68

4T60/65E ratios are
1st-2.92
2nd-1.57
3rd-1.00
4th-.71

There are a few different final drives for the 4T60/65E that will work in these transmissions BUT becaues the gears are of different tooth count and none of the other ratios are HD diffs I dont think the gearing changes between the two as the diff case is different sized for the gearing. IIRC the choices are 3.29 as the HD diff is, 3.05, and 2.86 for NON HD

Nope the internals are much larger and heavier in the 4L80E. The old THM400 uses the same gear ratio also, minus OD. Most guys want to go with a 2.75 1st gear conversion in those transmissions, Ive never heard of anyone wanting to go backwards! GM used the lower ratio in 1st for better in town acceleration. The 700R4 was originally designed for trucks and that is how the 3.06 ratio in 1st came into play and they never changed it. With NA engines its crap with the HUGE drop from 1st to second gear, but with the L67 in the car it doesnt car since there is so much torque across the powerband.

Well if its a race car get a 4500 stall converter then it will always be in the sweet spot lol. After the car launches its never going to be at a low rpm again, so that really doesnt matter. A Lingerfelter book that I bought a long time ago talks alot about the engines' powerband matching the trans, and having a manual trans or 6 speed per say keeps in in a really tight rpm range through the ran where an auto works better with an engine with a broad powerband. He plotted on a graph the rpms through each gear in the quarter mile and from that graph you average out what rpms you are at the longest period of time and that is where you focus everything on, not the peak numbers or the low rpms just going into each gear. Again if my cutlass with an ugle 3.06 first gear and a 2200 rpm stall converter is really never under 5K the whole way down the track and watching that on a HPT graph doesnt have much to it, its a very flat line the whole run and the engine sits within an 1800 rpm powerband almost the whole lenght of the track. It isnt in first gear long and it hooks up very hard, there is no wasted time feather or easing into the throttle, its WFO when the tree drops and hang on!

Originally Posted by Trannyman95

With NA engines its crap with the HUGE drop from 1st to second gear, but with the L67 in the car it doesnt car since there is so much torque across the powerband.

That explains why the GTs' pull till about 35-37mph then bog out, the gear change (if it were possible) would really help out the NA crowd, but then again none of us stay NA for that long