4T65E to 4T65E-HD

**robmurt90** · 08-21-2012

I did search but I feel like every other page I get a different answer haha, I have a 1998 Grand Prix GT (3.8 N/A) that needs a transmission, my buddy has a 2002 Grand Prix GTP (3.8 SC) that's wrecked. I was wondering if it was possible to just bolt the 4T65E-HD in place of my 4T65E with out any other motifications? Some posts I was reading said the PCM needed retuned and others didn't. Just want to make sure I can use it or not before I spend the time to swap them or pass up on a free transmission.

Thanks for any help.

**Fivefingerdeathpunch** · 08-21-2012

Car would need to be custom tuned.

GT is 3.29 and GTP is 2.93 gear ratio

**robmurt90** · 08-21-2012

Okay that's what I thought, just wanted to make sure I was understanding correctly. Thanks

**matt5112** · 08-21-2012

PCM has to know which final drive your trans has.

Passenger axle is different as well.

Flex plates in those years were only drilled for one torque converter.

GT recieved a 240 mm converter, GTP 258 mm.

**BillBoost37** · 08-21-2012

M.... NA was 245mm, SC 258. some other bodies had 258mm for both. (you know the ones..lol)

The transmission cooler line connections also changed.

**winterstorm** · 08-21-2012

you're gunna lose torque if u put the 4t65eHD in there because of the lower ratio. i would just modify yours and make it heavy duty. im not too familiar with transmissions so i wouldnt know how to do it, but im sure it can be done. do that or save your money up for a tranny from triple edge performance.

**BillBoost37** · 08-22-2012

Wstorm - Take a non-hd and put a HD diff in. Poof... HD with the same 3.29 ratio.

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