Aode/4r70w

Treneth said:

Good day gents!, looking for some of your guys opinions, one of these day I'm likely going to blow my c4 and swap into a 4r70w. I'm wondering how low rear end ratio a guy could go with before its hardly streetable, I have about 10km( yes km I'm canadian lol) of highway to get into town with the 3.55 and c4 I have now I can tolerate though not the most ideal. Could a guy go into 4.10 maybe 4.30 with a 4r70w and still do some highway without revving through the roof?

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You won’t need to change out the gear at all if you swap to a 4r70w. A c4 first gear is 2.46. A 4r70w has a 2.84 first gear. Swapping to anything more than a 3.73 will make a 4r70w first gear useless.

The transmission has 4 internal gears that multiply the rear gear ratio.
The C4 has 3
The C4's first gear is 2.46, the 4R's is 2.84. Multiply the 3.55x2.46, or 2.84 to get the effective total gear multiplication.
If this car has street tires on it, the 4r first gear will be effectively over 10:1
Basically just a tire blazer, made even more insane by adding a rear gear over 4:1

Depends on RPM capability. If your engine can spin a few RPM (6500+) and still make power up there, first gear might not be as useless as you think. Also depends on the converter and the programming of the 4R70W.

It's possible to swap in the AOD planetary gearset so that you'd have a 2.46 first gear. Many swap 4R70W gears into AOD's so they are in fact backward compatible but just to be fair, it's not a direct swap. That way you'd have a usable low gear AND overdrive.

For rear gear, if you have 3.55 now, with the 0.70 OD the engine RPM would be then effectively be like having a 2.48 final drive. So yes you could theoretically run with a 4.30 rear gear and it'd be like having a 3.01 with the OD. If you swapped to the AOD gearset, that'd drop a little as it's OD ratio is higher (0.667 vs 4R70W .70). Example if you are at 3000 on the freeway right now with 1:1 C4, with 4R70W, you'd be at around 2100. With AOD gearset, about 100 RPM less.