Engine swap / Trans swap 2001 gtp v. compatible years

**Banana Hammock** · 06-29-2016

I have a 2001 gtp roller than I am trying to get on the road again. I have been hearing different things regarding which year engine / trans I can use.

I picked up a '98 3800 gtp engine but I was told that it would not work due to the engine wiring harness being different? I would assume if this is the case I would just need a 2001 engine harness from a local junkyard? As far as I can tell the blocks are the same between the '97 - '03? I was also told that the only trans I can use is a 2001 otherwise I will have issues with the PCM.

I was hoping someone here in the know would be able to educate me on what I can / can't use.

Thanks

BH

**Fivefingerdeathpunch** · 06-29-2016

Wiring harness should be super similar, not much will be different if anything. Depends on if the car has cali emissions or not.

You will need a 99+ throttle body and MAF sensor through if you are using the 2001 computer.

The motor will swap over fine.

Any transmission that is a 4T65e HD from 1997-2002 is a direct swap. 2003 was the change over with valve body and internal controls.

**Banana Hammock** · 06-29-2016

Originally Posted by Fivefingerdeathpunch

Wiring harness should be super similar, not much will be different if anything. Depends on if the car has cali emissions or not.

You will need a 99+ throttle body and MAF sensor through if you are using the 2001 computer.

The motor will swap over fine.

Any transmission that is a 4T65e HD from 1997-2002 is a direct swap. 2003 was the change over with valve body and internal controls.

Thank you for the reply. I did have a 2002 gtp tranny sourced but the salvage shop selling it swore up and down to me that the gearing was different and that it wouldn't work.

**Banana Hammock** · 06-29-2016

Which tranny would I be looking for since I have a 2001?

4T65E HD W/internal neutral safety
4T65E HD W/external neutral safety

**Bronco Boy** · 06-30-2016

Originally Posted by Banana Hammock

I did have a 2002 gtp tranny sourced but the salvage shop selling it swore up and down to me that the gearing was different.....

This is correct.

**BillBoost37** · 06-30-2016

Technically you can use either trans. Then if you buy an internal range selector one, just put the external range on it and poof.. it's external.

Literally the selector just bolts on the outside.

**Fivefingerdeathpunch** · 06-30-2016

Originally Posted by Bronco Boy

This is correct.

The 2002 GTP didn't get different gearing. All GTP's got 2.93's from the factory. A 2002 transmission will fit in a 2001 just fine.

The standard SE and GT transmission have 3.29's and the impala's and bonnevilles got 2.86's and 3.05's as another option.

**Scottydoggs** · 06-30-2016

if you cant find the tranny you want, gear wise, it can be changed in the pcm.

**Bronco Boy** · 06-30-2016

Originally Posted by Fivefingerdeathpunch

The 2002 GTP didn't get different gearing. All GTP's got 2.93's from the factory. A 2002 transmission will fit in a 2001 just fine.

The standard SE and GT transmission have 3.29's and the impala's and bonnevilles got 2.86's and 3.05's as another option.

My bad. I thought he was gtalking GT to GTP. I reneg my previous statement. LOL

**Banana Hammock** · 07-02-2016

Originally Posted by Fivefingerdeathpunch

The 2002 GTP didn't get different gearing. All GTP's got 2.93's from the factory. A 2002 transmission will fit in a 2001 just fine.

The standard SE and GT transmission have 3.29's and the impala's and bonnevilles got 2.86's and 3.05's as another option.

Will any of the later years also work "'97-'00" ? From what I understand a 2003 will not work as it is different?

**Fivefingerdeathpunch** · 07-02-2016

I already answered that question in my first post.

Any transmission that is a 4T65e HD from 1997-2002 is a direct swap. 2003 was the change over with valve body and internal controls.

**Banana Hammock** · 07-05-2016

Originally Posted by Fivefingerdeathpunch

I already answered that question in my first post.

I don't mean to post redundant questions but I just don't want to waste my money on something that won't work. I called around today to price transmissions out and every place I called swore up and down that only a 2001 tranny will work.

**Fivefingerdeathpunch** · 07-05-2016

That's why I never ask them what they think because they don't know anything and only a select few do. I tell them what I want and if they have it great and if not I find it somewhere else.

You can search this topic up and down with the same answer in the end. The transmission MUST be from 1997-2002 and from a supercharged vehicle for it to be a direct swap. Anything newer than 2002 will not work and anything that came from a regular NA 3800 from a GT/SE or any other car like a buick/chevy will not be a direct swap.

There is nothing special or any different about any transmission made in 2001, they did not change gear ratio, case design, valve body, diff housing, axles etc etc etc, it is exactly the same as the years before.

**Banana Hammock** · 07-05-2016

Originally Posted by Fivefingerdeathpunch

There is nothing special or any different about any transmission made in 2001, they did not change gear ratio, case design, valve body, diff housing, axles etc etc etc, it is exactly the same as the years before.

That seems to be what I am finding while searching the transmission subforum on this site.

What do you think I should pay for a used one? The going rate for one from a salvage yard around here is about $350 including core.

**Fivefingerdeathpunch** · 07-05-2016

That price isn't bad at all and hopefully they have some sort of warranty incase it breaks right away. Some have like 90 day returns or something like that.

Lower mileage the better for sure and with anything used it's always a toss up on if it will last a long time.

**Banana Hammock** · 07-05-2016

Originally Posted by Fivefingerdeathpunch

That price isn't bad at all and hopefully they have some sort of warranty incase it breaks right away. Some have like 90 day returns or something like that.

Lower mileage the better for sure and with anything used it's always a toss up on if it will last a long time.

Pick n pull in my area is running a special where I can get a tranny for under $150 but the downside is not knowing anything about it.

**BillBoost37** · 07-05-2016

If you'd like to increase your chances of getting a better price.

Look up
99+ Bonneville SSEi
99+ Park Avenue Ultra
Buick Regal GS

They all have the same HD transmission as the GTP. Only difference is on the Bonneville and PA...the dipstick tube is different. It's held in by a 10mm bolt.

**BrandonHall10** · 07-05-2016

Originally Posted by BillBoost37

If you'd like to increase your chances of getting a better price.

Look up
99+ Bonneville SSEi
99+ Park Avenue Ultra
Buick Regal GS

They all have the same HD transmission as the GTP. Only difference is on the Bonneville and PA...the dipstick tube is different. It's held in by a 10mm bolt.

And statistically, those three are far less likely to see the kind of abuse a GTP trans sees.