Thread: Engine/Trans assembly swap

First off im new here so hello to everyone! I currently have an 06 grand prix base model 3.8 non supercharged with 209k miles with rod knock and also a very shady trans I have found an 05 donor car that got hit in the rear end runs and drives good wanting to swap engine and trans from 05 to 06 but when calling junkyards and LKQ they say it wont work that the 05 isn't compatible with the 06. it has always been my understanding that the grand prix from 04-08 was 3.8 series 3 didn't realize there were changes done. if anyone could shine some light on this subject for me and let me know what I may or may not have to swap over or if its even possible to do. again wanting to take engine and trans as an assembly from the 05 and install it into my 06. thank you in advance!!

Agreed. Only strange years are 04, which some I've seen the old oil pan and mount, and 08 which some switched to can-bus protocol and a new ecm that won't work, but you can swap your wire harness and it'll work. Good luck with the swap! Bill Boost has a really good engine/ trans removal how- to btw.

Awesome! Thanks for the quick and helpful responses. I didn't think there was any reason the trans and engine wouldn't swap over but I figured id ask to make sure. Last thing I want to do is tear them both out hold up the car and shop space more than im already going to. Thanks again very much appreciated!

Not trying to beat a dead horse here or question the ones who answered me but called the GM dealer and gave them both the VIN numbers off of each car and they looked up all sorts of parts like intake, sensors, oil pans, engine harness and trans gear ratios and all come back the same only thing I didn't have them check is the cams or any timing stuff. I called other junkyards and they are saying the engine wont swap over also and I work at a dodge dealer and one of the service guys is saying there could be a slight issue with cams or timing maybe? So I called LKQ talked to a guy there and he said that their system does not tell them why it wont work it just tells them it wont work they said if you can switch something then their system will tell them that but it doesn't they said it could be something as little as a bolt hole in the block for an accessory or plumbing to bolt to that is different. If I could get some more insight on this that would be greatly appreciated im trying to avoid taking 2 engines/trans assemblies out and be stuck and then have to either put the stuff back together or get an engine/trans assembly separate in who knows what amount of time. Thank you!

As long as the trans. going in is the same gear ratio and not from a supercharged car it should swap in. It's when the gear ratios are different that you run into issues. As far as I know the Series III N/A is the same in any car. Heck, I know people swap these motors into the 97-03 cars so I don't see what the difference would be. Engines should be exactly the same.

**UPDATE** Finally got to talk to my normal guy at LKQ and he knows his stuff he said engine displacement is different from 05-06 so apparently that's why I cant swap engines. Anybody care to enlighten me on if that's true or any way around it? Thank you

Your normal guy needs an info update:

3.8L L26 N/A V6
3.8L L32 Supercharged V6
5.3L LS4 V8

Only engine options in the 7th gen cars.

H

3.8orsepower

Ok then not sure where to go next with that I already know the engines that are available but apparently the internals were changed from what he tells me and that changes displacement slightly enough to not work but they are still 3.8 liter series 3 engines. Can anyone give me some in depth information on this swap I am thinking about doing? Will it work no issues? Will just the engine swap not the trans or will both with no issues at all? Thank you!

Originally Posted by lovemeagrandprix

Ok then not sure where to go next with that I already know the engines that are available but apparently the internals were changed from what he tells me and that changes displacement slightly enough to not work but they are still 3.8 liter series 3 engines. Can anyone give me some in depth information on this swap I am thinking about doing? Will it work no issues? Will just the engine swap not the trans or will both with no issues at all? Thank you!

lol he's flat out wrong. The displacement is identical. Identical pistons, identical heads, identical connecting rods. He's probably thinking from supercharged to na which yes, there's a different displacement. 04 is really the only "odd-ball" since it still uses the non-powdered connecting rods, some have the old oil pan, and a few other minor changes, but there were no other major changes until 08 when they switched to a new pcm.

On the transmission, as I've rebuilt quite a few of these, I can guarantee there's no incompatibility from 05-06 except from tapshift (comp-g), and of course from LS4 (bell-housing and a few other things are different).

How is there a displacement difference from an N/A motor to an S/C motor? The only difference I can see would be the positive displacement of the Eaton SC and that is air, not physical cylinder size. The base motor should still be a 3.8L, unless I've missed something that you could expand on??

This is why I like car-part.com. They usually show anything that fits within the year range, even if it's not from the exact car.

Originally Posted by FordMan77

How is there a displacement difference from an N/A motor to an S/C motor? The only difference I can see would be the positive displacement of the Eaton SC and that is air, not physical cylinder size. The base motor should still be a 3.8L, unless I've missed something that you could expand on??

Haha nice catch! And yes, you are correct, I meant to say compression ratio. That's what I get for typing on my mobile phone!

Bottom line, whoever is telling you this bull obviously knows way less about these engines than he thinks.

When I went on car-part.com 04 only works for 04, 05 only works for 05 and 06 goes from 06-09 so I went ahead and called a junkyard they confirmed that then I called LKQ and they also confirmed that and told me yes either displacement or compression ratio was different I cannot remember exactly which one but they said that's why I an engine from 05 wont go into an 06. Trust me if it wasn't for taking up my buddys dads shop and my buddys time I wouldn't care id just try it and see but im trying to avoid wasting his time or his dads space my car being down and excessive future alcohol consumption due to frustration haha. At this point in time im thinking about not even worrying about swapping the trans and engine as an assembly and just doing the trans but like I said in my first post my trans is being very shady and my engine has rod knock and they both as far as I know have 209k on them and car was women owned since 130k so im sure its time they both be replaced lol

Could there be tiny differences in the wiring harnesses between years?

But what others have said, it will work. I would leave the harness on the donor engine and trans and use that.

Originally Posted by lovemeagrandprix

Ok have an update talked to a junkyard someone referred me to and they told me that the 05 has 220 CID and the 06-09 has 231 CID and that is apparently the difference so im sure it will work but the programming may not so there may in lie the problem. im just so confused as to why there would be a change in CID (cubic inch displacement) from 05 to 06 that sounds so stupid to me and not right.

Lol sorry man, but they clearly have no idea what they're talking about... there is no difference. All 3800s have 231 displacement period... it's an error in their system