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Motor swap - Options

Cougar281

Cougar281

New member
My primary area of expertise is with Duramax engines and Allison Transmissions, so please forgive my newb questions.

A friend of mine has a 2004 Grand Prix GT. He was considering getting rid of it, but if he could make it more fun to drive (IE: more power :cool:), he'd keep it for a long time, like me.

I read over the top swap thread, and I'd rather not do that. I'd rather have the lower static compression of the L32 and maybe run a touch more boost than have the higher static compression +boost of a top-swapped motor. Do the GT & GTP use the same PCM, with only the programming being different? IF we go this route, my plan would be to pick up a motor and transmission from a GTP and drop them in, along with the GTP's PCM (Assuming it's the same), unless EFILive releases support for that PCM and I can get a GTP's tune. What PCM does the 04+ GT & GTP use? It looks like it MIGHT be an Atlas PCM (it appears to have a 56-pin C1, 73-pin C2 and 56-pin C3, which both the Atlas PCM and E40 ECM have, although I know it's not an E40)

The other though I had was a GXP's 5300 LS4. Near as I can tell, the LS4 weighs 478#, but I can't find any weight info on the 3800. Since the 3800 has an iron block and the LS4 has an aluminum block, I'm thinking that the two are likely similar in weight. I'm going to "study" the electronics on the GT/GTP/GXP's, and maybe even see if I can find an intact GXP to look under the hood, but on the mechanical side, does anyone know if the motor mounts differ between the two on the cradle side? They're probably different on the block side, but will the LS4's mounts bolt into the GT's cradle? I read the one thread I found related to a LS4 swap, but there wasn't any useful technical info. The advantage to swapping in a LS4 with the E40 ECM & T42 TCM is I can tune them with EFILive. If the LS4 will physically fit without TONS if work, I might be more inclined to go that route if I find the electronics won't be more trouble than swapping an 04 Mustang GT PCM into my 95 Cougar (which was a lot of work, but it works, save a few DTC's I need to iron out).

Edit: On quick look at the GXP's computer data lines circuits, it appears that, like the 06/07 LBZ Duramax powered trucks, the ONLY thing GMLAN is doing in the GXP is ECM/TCM/DLC comms, so if we went that route, I'd need to add GMLAN to the DLC for diagnostics only. The ONLY difference between the Computer Data Line schematics for the 04 GT & 06 GXP is the addition of the GMLAN between the ECM, TCM & DLC.

TIA!
 
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Well ill be the first to say that the ls4 has no aftermarket and you would be better going the l32 route. The pcms are the same the programming is different for boost obviously. Should be a straightforward swap for you if you have all that experience.
 
minichopper6hp said:
Well ill be the first to say that the ls4 has no aftermarket and you would be better going the l32 route. The pcms are the same the programming is different for boost obviously. Should be a straightforward swap for you if you have all that experience.
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Well, He's not like me and always tinkering, so the aftermarket (or lack thereof) for the LS4 is of little or no importance in this case. If it was for MY car, then the aftermarket availability would be more important, although, no offense, but as nice as the GP's are, I'd never own a FWD car. RWD or AWD/4WD is my preference. If swaping in the LS4 isn't significanly tougher than the L32, he may rather go with the LS4 swap for the ~100HP increase instead of ~60 with the L32.

Interestingly, it looks like the LS4 uses (almost) the same 3.29:1 4T65E-HD transmission as the Supercharged 3800 Series III... Hmmm....
 
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I think we're probably going to go the 3800 route, mainly due to cost; having said that, is there any reason we couldn't use a L32 and 4T65E-HD out of a 2005-2007 GTP? Car-part doesn't list anything other than 2004 as compatable, but of course, they're not the absolute answer. I'd rather get a newer motor & transmission with low miles if at all possible. I know some say the stock 4T65E can hold up to the supercharged motor, but considering the cost of the HD upgrade vs what a used low mile HD trans can be had for, it kinda makes sense to get the used low mile trans than to upgrade the 80k one. I want to minimize reliability problems, so I'd rather have the trans that's supposed to be under it there.
 
Heres the thing. Trans are the same. Diffs are not. If you swap the diff to hd diff, you can have the 3.29 gearing. If you swap the whole trans you will have 2.93. If you want a stock tune you can go the route of swapping the whole motor and trans and just get a stock gtp pcm. If not, you will have to custom tune for the high compression and different gearing.

That being said, i would just top swap it and change out the diff. If you have a junkyard near you then it shouldnt cost too much and you said you can tune, so there ya go. Any 04 and up has the l32 and the diff can be from 97-08
 
Actually, I can't tune the 3800. EFILive currently doesn't support it (although it's supposedly "in the works"). If needed, I can see about getting a used copy of HPTuners to do it, but wouldn't be my first choice. Not going to do the headswap, just a direct motor swap. I'm assuming only a supercharged 97+ would have the HD Diff? I've seen I think 3 supercharged Series II's in the yards I go to (they're gone now). I'll have to keep my eyes open. If I find one, I'll probably grab the diff, cover and axle. So I'm clear, his car has the 3.29, but the GTP came with a 2.93? Is anyone familiar with tripleedgeperformance.com? If keeping the current trans and upgrading it, I'd prefer to do a full rebuild. How compled is the 4T65E compared to an Allison 1000?
 


I dont know never dealt with the allison. Are you a tech? If so you should know how to do that shyt. 97-08 supercharged has the diff, housing, and axle you need.
 
minichopper6hp said:
Are you a tech?
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Not exactly... Shadetree mechanic, more like. Like I said in my opening post, I'm much more familiar with the Duramax engine, Allison transmission & GMT-800 & GMT-900 platforms; I'm tinkering with my truck all the time. I've done two Performance Allison builds, and have at least another coming. Going to be swapping an LBZ Duaramx into my 04. I've taken a Ford 4R70W apart, but never a FWD transmission. The Allison is easy, the Ford wasn't bad. Just not familiar with the internal workings of a FWD trans. More familiar with Diesel tuning than gasser. Mechanical stuff on pretty much any engine is cake.
 
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its not bad. You can get an astg manual to make it easier. Pretty straight forward if you have ever rebuilt an auto.
 
All other things being equal (driving style, mainly), what's the reliability of a top swapped motor vs a stock L32? I'm really on the fence between recommending the top swap vs dropping in the L32. One problem with the top swap is we'd NEED a tune; dropping in the L32 would mean we could run it with the L32 PCM no problem. Or can the L32 tune Adjust for the top swap?

A Few things I've gathered that sound like they would be a good idea regardless of which route we take (top swap or L32 drop-in) are:

3" DP
Headers
Rockers (1.9?)
Shift Kit

If doing a top swap, any headwork recommended to help performance? On the plus side for doing a top swap, aside from the supercharger, there's almost nothing mechanical (IE bearings) to worry about; just valve guides & seals, and valve seats).
 
Headers come with their own DP.

Rockers are a good idea for more high end power if you don't want to go for a cam.

You could run a top swap on an L32 PCM but thats just so it will move, you can't do any full power runs without a proper tune.

No porting needed unless you're going for a big cam. Supercharger wouldn't need to be ported at all either.
 


Polishing the combustion chambers, exhaust ports and smoothing the runners to 80 grit finish on the intake is what i would recommend. All would help knock retard which would be the main thing on the top swap.
 
drop in an l32 with trans and computer and run the car with a stock l32 tune.

top swap your gonna need custom tuning.

just drop in an l32 and call it a day.
 
i hate how everyone leg humps on the l32 like its 100 times better than the l67. the l67 is SO CHEAP.

also, anyone building an m90 setup that goes with a low compression block is pretty dumb anyway.
 
hes trying to have an easy swap. doesent really care about a build. does he really wanna go swaping all the electronics around to put an l67 in????

i mean i guess he could use the l67 bottom end with an l32 top end but if he can find the l32 for decent price why not. its gonna be a strait plug and play. if he gets the l32 pcm he wont have to do any tuning either.
 
blowfishRus6 said:
hes trying to have an easy swap. doesent really care about a build. does he really wanna go swaping all the electronics around to put an l67 in????

i mean i guess he could use the l67 bottom end with an l32 top end but if he can find the l32 for decent price why not. its gonna be a strait plug and play. if he gets the l32 pcm he wont have to do any tuning either.
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That, and why would I want to go backwards to a Gen III blower?

And it's not as much of wanting an "Easy" swap, as a reliable one. Driving style being equal, what's the difference in reliability between L32 top end on a L26 shortblock vs a stock L32 dropped in? My hesitation in going the headswap route lies in that usually, higher compression + boost isn't usually a good idea. Looking for a performance gain over the stock L26, but not looking to wring 350hp out of the 3800....
 
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they can both be dependable. but alot of tuning is needed to get a topswaped motor to run good and safe. that would be another problem you would need to conqour.
 
you need a bunch more supporting mods to run the higher compression even on the stock blower pulley. namely youd need headers and a good tune.
 
blowfishRus6 said:
they can both be dependable. but alot of tuning is needed to get a topswaped motor to run good and safe. that would be another problem you would need to conqour.
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Would a PCM from somewhere such as Overkill be "Good enough" to have the motor reliable, or would a Dyno tune be *Required*?

Bio248 said:
you need a bunch more supporting mods to run the higher compression even on the stock blower pulley. namely youd need headers and a good tune.
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I know he wants to do something with the exahust, so headers wouldn't be a bad idea anyway; I may go the route of finding a HD Diff & Axle in a local U-Pick yard, and at the time of the motor work, install that, recommend saving up for a trans build later, drain and fill the trans with a synthetic fluid such as Mobil 1 (Think Transynd would be ok? It's a synthetic Allison fluid made by Castrol that's Dex-III compatable) and using the money now for the supporting mods for a headswap (Lifters, plugs, T-Stat, Headers, Tune, some mild headwork, Shiftkit)
 
i agree exhaust would be needed for a topswap. there is some on here that run a caned tune like overkill with there topswap with no issuies. but it needs to be set up for a top swap. minichoper keep chiping pistions because he is topswaped and run a tune for the regular supercharged motor with lower compresion.

the trans will be fine as long as you dont absolutly beat on it and do your regular oil changes. bio had a gt trans in his car for a while with the supercharged motor and alot of mods.
 
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