Anybody here ever swap their 3400 UIM for a 3500 one? I plan on doing it in the future and yes i do know i will need a new throttle body and port my LIM.

 

I've never done the swap, but it's been popular for a wile to "top swap" a 3100 with 3400 parts and obviously as your planning a 3400 with 3500.

I've read a lot about this in the past and due to various minor changes GM has made once in a while, it's not always 100% cookie cutter (might be 90%+ cookie cutter). To get the most out of what you are discussing, you will want 3500 Head, LIM and UIM. Once it's done, you also need the car re-tuned.

I found this link where someone goes over the process briefly on his 3400 Grand Am (much if not all of it applies to the Monte):
3500 Top End Swap Complete

And this shop can sell you a full top swap kit:
3500 Top Swap (w/ ported intakes and gaskets!) - Milzy Motorsports

 

So is it possible to just do the uim without having to get the 3500 head? Im not looking to make my car super fast, just kind of little performance. And yeah i'll tune it too

 

Unfortunately, that I'm not certain of (never had the parts to play with). I'm going to guess it will fit. If you already have the UIM, it may take roughly an hour to test that theory.

Keep in mind, the gains from swapping the heads, LIM and UIM is bigger air flow through the entire system. If you swap only the UIM, the 3400 LIM and heads are probably still going to be restrictive, preventing the best gain from the mod. The thing I don't know is how restrictive (I'm guessing the 3500 UIM with a bigger throttle body will still yield an improvement).

If you have any junk yards that you can pull the parts yourself, you may want to price out and give thought to a full top swap and get the most from it.

Food for thought.

 

Yeah there's a few junkyards like that around me. Is the monte carlo 3500 the only 3500 heads, uim, and lim?

 

That will fit on my car

 

You pretty much need the 3500 LIM and UIM... I believe the heads will fit, but the 3500 heads likely flow better. If you can get it all I would do it. That being said, I believe if you are able to find two rear 3500 exhaust manifolds, they are like 'shorty headers' you'll just need to make a crossover.

The throttle body unfortunately isn't going to transfer as they changed the drive type, but everything else should swap over. The 3500 is just slightly larger bore than the 3400, same core engine.

 

What Mitch said lol!

As for the 3500, the heads, LIM, UIM you can get from any GM 3500 powered car (Monte, Impala and a few others).

The exhaust manifolds (if you are going to use 3500 mani's), you may need the Monte or Impala ones due to the geometry on them. But I honestly know nothing about the exhaust manifold pros/cons....

This would be a cool project to grab pics of and share as you go through it!!!

I know other 3400 guys have had interest in spending a few more bucks for power and this swap with documentation would be an awesome share for those guys!!!

I compiled this thread a while back for people looking more at the cheaper end of power and mods for the 3400 cars:
https://montecarloforum.com/forum/fw...p-power-46071/

I'd love to add a 3500 top swap to the FWD Tech Guides if someone did it and made a great guide from it.

 

Something tells me this is going to be a bigger project than i thought. Not sure if i will ever have the time or money for it though. Might just resort to doing an exhaust and tune instead. Maybe i'll do this way into the future.