Gearing change in 4T60E, Chip need to be changed?

[dbtk2]

I am hoping to buy my friends '93 Lumina from him and put in a 4T60e with 3.43 final drive (from a DOHC engine) and possibly put the 3.33 differential out of his bad tranny in the new (used) one for 3.73 final drive. (I was told that all you have to do for 3.73 gearing is put the 3.33 dif in the 3.43 tranny) However, if I am going to change the gearing, to 3.43 or 3.73 I am going to need to get the chip changed correct?

If so, what would it cost to have this done, and also all of the normal stuff thats done to the chips?

Thanks,

Shawn

[TheProfessor]

yes im pretty sure you would

[SappySE107]

Its the shift points that need to be changed mostly, and I don't know what you would want them to be exactly. Its based on MPH and not RPM so its a bit difficult for me to guess.

[dbtk2]

Yeah, I know its based on MPH... I just wanted to confirm that the computer does in fact need to be changed.

Shawn

[SappySE107]

Only if you want it to shift at the same shift points it used to for RPM Otherwise its gonna tach up higher.

[dbtk2]

Well, I would probably leave the shift points at the same spot for 3.43 gears, but with 3.73's there is no way I could do that. Then I would just raise the limiter and get all of the regular chip changes done to it.

Wouldn't the gearing difference make the speedometer off? I know on L67's if you change the gearing you will get a SES light and the speed will read wrong...

Shawn

[SappySE107]

Nope, no issues with the speedo that I have found. Definetly no SES light:P Have to ask someone with that done though if they noticed a difference with the speed vs one of those radar signs that tell you your speed.

Im in indiana so if you wanted to test out the shift points and make changes, we can probably arrange someone to meet up and do that.

[dbtk2]

That sounds good. We might have to do that come spring when (hopefully) this project is done.

Shawn