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1999 Pontiac Engine And Tranny Swap

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PGT

New member
Hey i was going to place a 1999 buick regal ls engine and tranny in my 1999 pontiac grand prix gt becuause i need both and was wondering if it would fit without any problems. Thanks
 


Thanks but ah i also heard that the differential ratio was different as well as the Converter diameter or that wouldnt b a problem
 
As long as you're taking the whole engine and transmission, the converter size doesn't matter. If you grab the wire harness and PCM from the donor car, you won't have to worry about the different gear ratio.
 


HOLD ON A MINUTE!

The diff ratio is different, 3.05 in the Regal vs 3.29 in the GP GT. This means you would need to reprogram your computer, since I'm pretty sure you can't use a Regal computer in a Grand Prix (BCM issues, I believe). If the diff in your current trans is still in good shape, you could swap that in and you should be fine with your stock computer.
 
Scimmia said:
HOLD ON A MINUTE!

The diff ratio is different, 3.05 in the Regal vs 3.29 in the GP GT. This means you would need to reprogram your computer, since I'm pretty sure you can't use a Regal computer in a Grand Prix (BCM issues, I believe). If the diff in your current trans is still in good shape, you could swap that in and you should be fine with your stock computer.
Click to expand...


So even if i just drop the tranny in it would not work at all because i thought the diff ratio wasnt that big a deal
 
Scimmia said:
HOLD ON A MINUTE!

The diff ratio is different, 3.05 in the Regal vs 3.29 in the GP GT. This means you would need to reprogram your computer, since I'm pretty sure you can't use a Regal computer in a Grand Prix (BCM issues, I believe). If the diff in your current trans is still in good shape, you could swap that in and you should be fine with your stock computer.
Click to expand...

I thought GP BCMs were pretty accepting. It's the Chevy and Buick BCMs that give issues.
 
So it would b alright to go ahead and drop the whole tranny in out of the buick into my grand prix with no problem at all then or is there anything i have to keep in mind
 


If you run a 3.05 diff when the computer thinks you have a 3.29, it'll throw a code and max out the line pressures, it'll be shifting at the wrong times, your speedometer would be off, etc. Not a good idea. Either reuse your current diff, get another 3.29 diff, or reprogram your computer.

Sabrewings, I know for sure you can't use a GP PCM in a Buick, and I've always been told you can't go the other way, either. Even the gauge clusters in the Buicks get their signals differently than the GPs. Mechanically the cars are pretty similar, but electrically the Regals and the GPs have quite a few differences.
 
So how would you go about reusing the same differential out of my current grand prix transmission and into the the buick transmission or reprogramming the computer.
 
Scimmia said:
Sabrewings, I know for sure you can't use a GP PCM in a Buick, and I've always been told you can't go the other way, either. Even the gauge clusters in the Buicks get their signals differently than the GPs. Mechanically the cars are pretty similar, but electrically the Regals and the GPs have quite a few differences.
Click to expand...

I wish I still had my GM SI manual installed to look at the differences. :th_angry2:
 
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