Transmission Swap
 

I've been reading about Brandon Furches' LS4 Monte, and was wondering a few things. In this article (https://www.thedrive.com/news/25998/turbo-ls-swapped-2004-chevrolet-monte-carlo-makes-766-hp-at-the-front-wheels) it says Brandon swapped a 4t65E from the LS4 that was put into the Monte. If I'm not mistaken, that's the same transaxle that comes with the 3800. Unless it's a variation specifically for the LS4? If it is the same, then theoretically you could (with heavy modification) fit the same 4t80 that Brandon swapped into his LS4 Monte?

The 4t65e was used on a LOT of w-body cars. 3800(L36/L67)/3400/LS4, I believe the 3500 and 3600 and 3900 as well.

In theory, I think you are right, you could pair up a 4t80 to a 3800/3400. But, you have to check for differences. Such as, was there any mid-year weirdness with mounting? Computer or non-computer controls.

Keep in mind, in our cars, the PCM drives the engine AND the transmission. I read Brandon used a PCM from an Express Van on that build. I asked why and the biggest answer was so the gauges and such in the 2004 Monte would still work with the engine swap. I have no idea what role the PCM does or does not play with the transmission he is using. If I recall, wasn't the 4t80 he got from an early 90's Caddy?

Yeah, I believe that's where the article said he pulled it from. But there was also a quote from him saying he could use just about any 4t80, cause they're super abundant.

The engine trans and mounting were all custom.

From an LSX Mag article: "Fortunately, there was some literature on the Sloppy Mechanics Wiki page, which allowed him to almost treat it as a stand-alone, full manual control; similar to that of Jake’s Performance 4l80e controller." Would be cool to find that info and see how it works.

I see Brandon Furches is active on a few different groups on Facebook ,maybe try contacting him directly. Most of the Monte Carlo owners are always willing to share information. If you do please start a thread as I'm sure many would benefit for what he did in that build. Good luck .

So your first post is confusing me. You are talking about 2 different types of transmissions as is they are the same.

The LS4 Monte, never came with the 4t80e that he is using in his build. A W-Body never came with that transmission. So you would be doing something custom to fit that to a 3800 powered w-body.

He was able to pull the 4t80e and use it, because GM used it on the LS4 for the G-Body cars. I don't know of anyone who used the 4t80e on a 3800. So the way to mate the LS4 to the 4t80e was already established by GM, but never in a w-body.

4t80 has been done on a 3800, it's certainly possible. It's not a bolt in, but it's fairly straightforward fab work. The electronics are a bit more of a pain, but as noted above you could always scrap all of it and do a full aftermarket controller in the worst case.

IMO 4t80 is the way forward for big power 3800s as the GMR parts continue to dry up and get to crazy prices.

The biggest downside I see is the weight. It's a far heavier trans and has way bigger internals, so with no other changes, the car will be a bit slower (no different than 4l60 to 4l80 swaps). The second downside I see is that there aren't really any major aftermarket companies supporting it. Certainly any good trans shop can freshen it up, or you can do what many have done and just keep dropping in $200 junkyard units until you find one that doesn't grenade.

That last part is the huge upside. They're silly cheap. So if you can do the mechanics and electrical yourself, you save a ton over a fully built GMR 4t65 (which may or may not survive either).

To expand a little more on why I think this is the way to go for high hp builds nowadays is the cost. Someone just getting into a new build today is looking at an easy $5-6k bill for a fully built 4t65 ($4200 for the highest TEP trans plus whatever you can find GMR parts for). Being that most these 3800 cars are barely worth that nowadays, it's tough for someone new to come in and dump that kind of money on it.

On the other hand, picking up a used 4t80, a used turbo kit, and either meth or an E85 conversion could be had for about what a built 4t65 alone goes for. Certainly that's still near the value of the car, but that's a lot more realistic for someone that planning to spend $10-15k on a 4t65 and all new engine parts. So at least it gives an option for more people to keep the platform moving a little longer.


I will say, the one tough part of the 4t80 is that the information is so scattered across the forums. I never came across a good thread that had all of the info in one place. Certainly it's out there, it just takes a lot of time to dig the info up.

This is the biggest issue. I didn't even know of w-bodies on the usual forums making that switch, where you say there's a few. I wish I could see those builds.

As far as the most informative threads about the swap itself, there is a good one from Pontiacjeff and one from turbo400sbc out on the net (just add 4t80 by their name on a Google search). Neither are applicable to physically bolting it into a w body, but they both cover the physical attaching it to a 3800 and some electrical.

I haven't seen a good thread about physically mounting it into a w body though. That Furches car was originally a L67 car and was able to fit a LS4 + 4t80, so certainly the width / space is there on non LS4 cars.

The worst part about many of these threads is that the pictures are usually gone, so it can be tough to follow. I looked into this a few years ago as I considered one for my monte at a point.


To be sure I'm clear about this, this certainly isnt an easy project for your entry level modder who has just done bolt on stuff. But for someone with fabrication and electrical experience, this is certainly on the easy end of the spectrum.