Doing some planning on a Camaro SS engine/trans pullout swap for my 77 C10 pickup. I'll be using an all-stock donor drivetrain, complete down to the ECU tuning and exhaust manifolds. I want this to be as stock as possible.

Looks like the stock tire diameter of the donor Camaro has pretty much identical sized tires (29.5" tall) to what is on my truck. However, an L99/6l80 equipped Camaro came with a 3.27 rear gear. My truck has 3:73’s.

Assuming I drop in the combo as is with my 3.73's, will this cause the transmission shifting to be completely out of whack? I guess what I’m asking, is what happens with the shifting on a 6l80 when you have a higher numerical gear than what the trans is factory tuned for? Early shifts? Late shifts? Will it even care?

I will be putting in an Eaton Trutrac differential sometime in the future, so a ring gear change to something closer to mimic the stock Camaro drivetrain isn’t out of the question if needed.

 

It will need to be tuned after the swap anyways.
When your tuner does his thing, he will insert the tire size and gear ratio and if using HP tuners it will automatically set the shift points and speedo calibration for you.

If you dont adjust the ECM for the gear ratio it will still shift ok since it will think your going faster than you actually are making the transmission shift earlier with 3.73s than with the 3.27's

 

Thanks for the info. When you say “it will need to be tuned after the swap anyway” are you referring to removing the VATS? Because if I can replicate the donor car’s final drive, there would be no need for a tune, correct?

 

As long as nothing changes it wouldn't need tune. If everything stays the same like MAF, intake tube size, similar exhaust, ect. But yes vats will need to be disabled and if that is being done with HP tuners you can easily returned the gear ratios in about 15 seconds

 

VATS will have to be removed before the engine will run. With HP Tunners you will have to purchase tokens to write to the PCM to remove VATS. Once you have purchased the tokens you are free to change whatever you like as many times as you like. So why not adjust the shift points?

 

Thanks again for all the info. This is all new to me (if you can’t tell). I’m an old school SBC carb guy
I guess when I say I don’t want to “tune” the trans I just don’t want to get in there and start modifying a bunch of factory parameters. If it’s as simple as plugging in my final drive ratio to HP tuners and everything “self adjusts” I wouldn’t mind that. I’m just not sure how it all works.
Regardless, it looks like there is no gear for a GM 12 bolt anyway that would let me mimic the Camaro’s 3.27, so I may just stay with the 3:73’s and adjust the PCM/TCM. GM truck 12 bolt ring and pinion sets seem to jump from 3.08’s to 3.40’s with nothing in between.