LS4 swap. Not a lot of chatter about this one? - Third Generation Forum

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LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 5:33 PM
My roommate has a 2008 GP GXP with an LS4. He has a couple of Fieros too. Being car guys we got started talking about putting his engine in a Fiero and a J. Its been done in a Fiero with a 6 speed F40 behind it so Ive got some reference material there. Basically Im curious why theres only like 2 threads about doing an LS4 swap. It has the same GM Metric trans bolt pattern as a 3x00 and LN2s and has a ton of aftermarket like an LS engine. 305 hp and 325 tq in stock untuned form. Its pretty wicked in a 3200lb car with traction control so it would be a force to be reckoned with in a 2500 lb one. Not to mention these engines have become VERY affordable since theyre kind of a bastard child.

I dug up a few LS1 dimensional diagrams. It wouldnt be exact for an LS4 because the 4 has a 13mm shortened crank and a slim accessory drive. If a 3800 with a S/C drive fits in a J then an LS4 should. The frame rail clearance in a W-body is very similar from what I remember. Obviously some sort of subframe would be necessary. Weight balance would be better than a 3800 maybe even comparable to a stock LN2 Cav.. All aluminum vs all cast iron. If its close I can sledge myself some clearance. My biggest problem is not having a J anymore to take measurements on.





I honestly dont think an F23 Getrag would have an issue with handling the torque as long as you arent doing launches on slicks or absolutely hot rodding the piss out of it but I could be wrong.

Exhaust might be a challenge but that should be the least of my worries. Sledge me some clearance.

Coolant and heater hoses arent really a concern. Theyre flexy.

Wiring would probably be the biggest hurdle in my mind. The LS4 is a drive by wire engine. So we would either need to run a modified pedal from an LS4 W-body with the proper DWB sensors or pick up an LS1 drive by cable TB and add in the IAC and TPS. GM was nice enough to leave that circuitry in a lot of its LS DBW PCMs. LS4 displacement on demand would be scrapped in the PCM because it requires input from the auto trans to selectively kill cylinders. DoD is junk anyways. The rest would be practically the same as any other piggybacking operation from what I can gather. Run the engine from the LS PCM and drive the gauges off the J PCM is possible. If not, @!#$ it and get some aftermarkets like Nota2.4. The beauty here is that the LS series engines have been dropped into soooooo many cars that there is more than enough electrical combinations out there to get what info may be needed. Tuning would be done via HPT as always.

As far as accessories are concerned I wouldnt be running most of them. Not big on P/S in a non DD car. A/C? I have windows. Hell even an electric water pump is available for LS's.

So does anybody have any other helpful input? Please dont say "Just go do it." Ive spent a lot of time researching and would just like a productive conversation or none at all.





Edited 1 time(s). Last edited Monday, March 25, 2013 5:42 PM



Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 6:10 PM
this is the most likely LSX swappable engien seeing as GM build it to be FWD the JCO has a member doin an LS1 but its gonna be tight as the LS1 is bigger
the getrags can handle it just cause it has a bunch of torque doesn't mean theres a lot of load on it because the transmissions are rate base on vehical weight. hens why grand ams got a 45E and some got 60E and j bodys got 40E transmissions

i think is someone wants to attack an V8 swap this would be it or the 3.6 engine would be cool both would not be cheap but interesting



JBO since July 30, 2001
Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 6:29 PM
I'd love to see it, but I'll be the devils advocate;

with the L67/F40 in my fire, I've got maybe 0.25" on each side of the unibody frame rails (and that might pushing it) so if the LS4 is even just a slightly longer I don't think it will fit without modifying the frame rails,
mounting the starter is going to be a @#$% because it mounts on the trans not the engine, so you'd have to cut into the trans and make a custom mounting bracket,
I don't think the wiring would be any more difficult than the 3800, but probably just as easy to go full stand-alone,
and it might just be easier to do a RWD conversion instead of trying to make it FWD

It's an interesting idea, I definitely wouldn't mind being able to pop my hood and see one of those sitting underneath. In for the discussion.



Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 6:33 PM
Is there a link to the LS1 swap? Id like to check it out if possible. Which 3.6 are you talking about? Ive got so many different engines swimming around in my head between the GM and import world haha.



Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 6:37 PM
Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 7:16 PM
Nic Crosby wrote:

I'd love to see it, but I'll be the devils advocate;

with the L67/F40 in my fire, I've got maybe 0.25" on each side of the unibody frame rails (and that might pushing it) so if the LS4 is even just a slightly longer I don't think it will fit without modifying the frame rails,
mounting the starter is going to be a @#$% because it mounts on the trans not the engine, so you'd have to cut into the trans and make a custom mounting bracket,
I don't think the wiring would be any more difficult than the 3800, but probably just as easy to go full stand-alone,
and it might just be easier to do a RWD conversion instead of trying to make it FWD

It's an interesting idea, I definitely wouldn't mind being able to pop my hood and see one of those sitting underneath. In for the discussion.


I forgot to mention the starter issue. The guy using the F40 in the Fiero cut a hole in his trans case to mount it.

Is your F40 any wider than an F23? Is it mounted pretty close to the stock trans location?

Thanks for the link Whitez. Good thing Im still a JCO member.



Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 7:29 PM
if it fits it'll be an absolute whore to work on.

still though.... go for it!



It's nice to be injected but I love being blown.
Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 7:34 PM
Cant be any worse than working on an LS1 in an F-body. @!#$ doing the back plugs. Hahaha



Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 7:36 PM
Yes it is wider, and even dry its heavier than an F23. The differential is also in a slightly different position in comparison to the bellhousing, lower and I think it sits farther back.

It has been proposed many times (and probably true), that the F23 can hold more power than F40. Especially the 2006 MT2, GM didn't do something right with that one, though the 2007 MU9 should be better and the saab versions even better.



Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 7:38 PM
^ same on a 3800 in an F-body, and it couldn't be any worse than the diesel Ford F-350 we had at work, had to pull the cab every time you needed to change the plugs.



Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 7:50 PM
Ive heard that about the F40s. Seems like everyone still loves swapping them into stuff.

Im hoping that you could get a car with an F23 in it and basically just use the factory mounts for the trans to simplify all of the axle geometry and that stuff. It just seems like the more you start to shift something here and angle something there more problems get created.





Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 7:53 PM
Nic Crosby wrote:

^ same on a 3800 in an F-body, and it couldn't be any worse than the diesel Ford F-350 we had at work, had to pull the cab every time you needed to change the plugs.


At least the glow plugs dont need changed as often as spark plugs or that would really really suck.



Re: LS4 swap. Not a lot of chatter about this one?
Monday, March 25, 2013 8:01 PM
Right. Do things as simply as possible the first time, to work all the bugs out as you go. You'd have to be mad to do it all at once *caugh*

Brian (TheSundownFire) wrote:

Nic Crosby wrote:

^ same on a 3800 in an F-body, and it couldn't be any worse than the diesel Ford F-350 we had at work, had to pull the cab every time you needed to change the plugs.


At least the glow plugs dont need changed as often as spark plugs or that would really really suck.


But the problem with that one is our driver for it kept blowing the engines. After about 3 it got traded for a newer GMC 4500.



Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 2:29 PM
I've been continuing to look into this, found an LS6 they swapped into a 01" Grand Prix, and they used an oil pan to mount the starter under the engine. Unfortunately it sounds like they only made 6 of those oil pans, but I've read you may be able to modify an LS1 oil pan to do the same thing. Also found that the length of a 3800 from crank to flywheel is about 24" as well, so the LS4 should physically fit in a J-body engine bay.

The swap looks completely possible, just a few other small issues to work out.





Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 2:48 PM
I have been really wanting to this swap myself. At first I wanted to do it with a 6t70E, but now thinking of doing it with either the F23 or F35/40. I'm leaning to the F23. Now I started thinking about if you start with an auto J and possibly swap in a subframe from a manual J to deal with the geometry angle? And good point about the Air Fuel Management System(DoD). Also I was planning on doing a header setup for a Impala or GP with an LS4 and go custom from there since GM routed the exhaust over the trans, but then again there is the linkage. But a definite change I'll be doing is a pair of valve covers from Holley that allow you to mount the coils onto them directly.

Subscribing for any info that can be worked out and dug up.


"United by Individuality"
"If life is a joke, why aren't we laughing?"
"Normality depends on one's perception of reality."
http://www.cardomain.com/ride/3820803
Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 3:10 PM
The subframes should be the same between auto and manual, the difference is in the mounts welded to the car. It would be easiest to start with a car with an LN2/F23, make a subframe extension like you would for a 3800, custom motor mounts, use fwd exhaust manifolds/headers with a modified downpipe (it should work with the F23 linkage, it works with the V6 swaps), custom oil pan w/ starter mount, wire it like Brian said in the original post, and figure something out for the clutch and flywheel.

It's a lot like a 3800 swap, just a little more work, a little more expensive, you get a little more starting power, less aftermarket, and you get to say you have a FWD V8 Cavalier/Sunfire.



Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 3:23 PM
Nic Crosby wrote:

I've been continuing to look into this, found an LS6 they swapped into a 01" Grand Prix, and they used an oil pan to mount the starter under the engine. Unfortunately it sounds like they only made 6 of those oil pans, but I've read you may be able to modify an LS1 oil pan to do the same thing. Also found that the length of a 3800 from crank to flywheel is about 24" as well, so the LS4 should physically fit in a J-body engine bay.

The swap looks completely possible, just a few other small issues to work out.


I remember seeing that oil pan before. I'm a little iffy on mounting a starter that low. I'm not sure what kind of ground and clearance we'd have in a J. Definitely interesting though. It is probably a little more forgiving than chopping a hole in an F23 case. I might need to try digging around on ArchieV8s sight. Hes done a lot with mounting SBC's in front of Getrags. Maybe he'll have something that could help out. On the topic od the clutch and flywheel, if we could verify that the LS4 and the 3800 run the same size flexplate and torque converter then it's be safe to say that we could use the same milled flywheel as a 3800 swap.

Thats good news on the block length. I've been digging for a cheap LS4 to buy and I've found a couple but I'm not in a position to do that kind of work in an apartment complex. Haha. Prices range from $2k to about $600 and a used F23 runs about $200.

macktruck84 wrote:

I have been really wanting to this swap myself. At first I wanted to do it with a 6t70E, but now thinking of doing it with either the F23 or F35/40. I'm leaning to the F23. Now I started thinking about if you start with an auto J and possibly swap in a subframe from a manual J to deal with the geometry angle? And good point about the Air Fuel Management System(DoD). Also I was planning on doing a header setup for a Impala or GP with an LS4 and go custom from there since GM routed the exhaust over the trans, but then again there is the linkage. But a definite change I'll be doing is a pair of valve covers from Holley that allow you to mount the coils onto them directly.

Subscribing for any info that can be worked out and dug up.


The only difference in subframes are exhaust cut out shape between the LN2 and the Ecos. Like Nic said everything is mounted to the frame rails in J's. Im only a fan of manuals because generally theyre more compact than manuals and I dont drag race and stick shifts make me happy. Plus its less wiring to deal with. It would be awesome if the headers that are available for LS4s would clear.

Im glad somebody else is interested in this. Im just hoping nobody else gets to it before I do!



Edited 2 time(s). Last edited Thursday, March 28, 2013 3:44 PM


Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 3:27 PM
Nic Crosby wrote:

The subframes should be the same between auto and manual, the difference is in the mounts welded to the car. It would be easiest to start with a car with an LN2/F23, make a subframe extension like you would for a 3800, custom motor mounts, use fwd exhaust manifolds/headers with a modified downpipe (it should work with the F23 linkage, it works with the V6 swaps), custom oil pan w/ starter mount, wire it like Brian said in the original post, and figure something out for the clutch and flywheel.

It's a lot like a 3800 swap, just a little more work, a little more expensive, you get a little more starting power, less aftermarket, and you get to say you have a FWD V8 Cavalier/Sunfire.


The trans mount is on the body and not the subframe? One other thing I would like to find out down the line is if the K-braces that are availible would in some way clear the LS4. I don't have high hopes for it, but it would be a great thing. But it's something yet to be seen.


"United by Individuality"
"If life is a joke, why aren't we laughing?"
"Normality depends on one's perception of reality."
http://www.cardomain.com/ride/3820803
Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 3:42 PM
macktruck84 wrote:

Nic Crosby wrote:

The subframes should be the same between auto and manual, the difference is in the mounts welded to the car. It would be easiest to start with a car with an LN2/F23, make a subframe extension like you would for a 3800, custom motor mounts, use fwd exhaust manifolds/headers with a modified downpipe (it should work with the F23 linkage, it works with the V6 swaps), custom oil pan w/ starter mount, wire it like Brian said in the original post, and figure something out for the clutch and flywheel.

It's a lot like a 3800 swap, just a little more work, a little more expensive, you get a little more starting power, less aftermarket, and you get to say you have a FWD V8 Cavalier/Sunfire.


The trans mount is on the body and not the subframe? One other thing I would like to find out down the line is if the K-braces that are availible would in some way clear the LS4. I don't have high hopes for it, but it would be a great thing. But it's something yet to be seen.


All of the mounts are on the body. Ive dropped the subframe out of a J before. All thats mounted to it is the control arms and the steering rack.

At this point Im not even going to speculate on getting aftermarket parts to work on an LS4 Cav. Theres too many stock things that Im not sure on.

I edited my post above yours while you posted. So I kinda double answered your question on accident haha.



Edited 1 time(s). Last edited Thursday, March 28, 2013 3:45 PM


Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 3:45 PM
I don't think the starter sits any lower than the lowest part of the oil pan, so I don't think there would be an issue there, and you could always just raise the engine a little bit to make clearance.

I have room to work on it (although outside) and a junk car to do test fittings in, but with my L67 project, I lack funds.

Yes, they're on the uni-body frame rail, not the subframe/K-brace. I don't think there will be an issue fitting engine with the subframe.



Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 3:50 PM
I wish GM Parts Direct was as well laid out as Honda Parts Direct is. I can cross reference PN's like a bad man with Hondas.

Digging for TC and flexplate specs. Cmoooooon. I am going to be at my friends salvage yard tomorrow night so Im going to dick around with their Hollander interchange to see if I can dig anything up.

Well GM tells me that all of the torque converters are same in both the 3800s and the LS4. It lists a different flexplate for all of them but IIRC the 3800 plates are the same thickness but have a wider bolt pattern for the TC bolts or something. I should remember because I just did a S/C to N/A swap like 2 weeks ago. In my mind we "should" be able to run the same clutch and flywheel setup as a 3800 swap. Same trans and the same TC. It would make sense unless GM did something funky with the length of the crankshaft and made up for it in the thickness of the flexplate.



Edited 2 time(s). Last edited Thursday, March 28, 2013 4:03 PM



Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 4:15 PM
Clutch maybe, but not the flywheel. The 3800 has a 8 bolt flywheel pattern while the LS4 uses a 6 bolt pattern. From what I've seen so far, it needs a 142 tooth flywheel for the LSx and they don't make one, but I would be curious to see if the LN2 uses the same 6 bolt pattern as the LSxs. If they were the same, that would make it easy. Otherwise you would have to go custom or auto.



Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 4:33 PM
It looks like the Ln2 uses a 6 bolt flywheel just like the 3400s. I couldnt tell you what the bolt circle looks like. But my friend has a wall of flexplates so Ill see what I can dig up.



Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 4:47 PM
3.1in x 60 pattern on an LS1 so safe to assume the LS4 is the same?

Maybe one of the friendly members here has a flywheel sitting around they could measure.

Are you saying that a 142 tooth is required to work with our starter or to fit in the bellhousing? If youre cutting a hole in the tranny you can monkey with picking a starter to get one that will match the tooth pitch.


Edited 1 time(s). Last edited Thursday, March 28, 2013 5:00 PM


Re: LS4 swap. Not a lot of chatter about this one?
Thursday, March 28, 2013 5:44 PM
It doesn't matter too much, a LN2 flywheel has 142 teeth. If the crank to flywheel bolt pattern and hub size are the same it should work.



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