Lot of the outside basics look identical. Would a basic computer retune be all that is necessary to adjust for the higher displacement? I wanted to get a low mile 98 or 99 Z-34 w/ the 3.8 but there with out rust or being all scuffed up but I just can't find one so I was thinking about this swap since there are still some nice 3.1 low mileage monte's out there. Thank you for all the help and info.

 

You could always just swap the 3.8 into the 3.1 Monte Carlo

 

Personally, I think if you're doing this for performance, you should swap in a 3.8. Much better engine, more powerful and more opprotunity for better performance mods.

I do know the N-Body community has had some people that swapped 3400's into early to mid 90's Grand Ams that originally had 3100's.... Here's a PDF someone made of "everything you need to do" as it pertained to his car. I'm sure their are some differences between this and a Monte, but it would probably give you a good start to what needs done:
http://crzyz28.sytes.net/images/bann...swap-guide.pdf

 

I believe that both motors use the same motor mounts, so they should physically fit in place. A difference might be gearing in the transmission, but if you swap the transmission out too, or retune the PCM with the new gearing, you should be able to over come that. There are probably several other things too that need to be done, but those are two big points.

 

You can't just retune the gear ratio....You would need to swap to a transmission that had the gear ratio you were looking for.

Just look for a 3.8L/ 4T65-E tranny combo and swap it.

As for the 3.4L from a Grand Am, yea it would fit, but the Grand Am's have a different transmission, so you would need to make sure it bolted to a 4T65-E tranny, and you would not be able to pull the engine and tranny from the Grand Am.

 

For giggles, I skimmed through that document (PDF) link I posted earlier. It talks about swapping a 3400 into a 3100 equiped '95 Grand Am. One BIG item... KEEP THE STOCK TRANS.... It mentioned that if you used the 4T65-E in a Grand Am, then you're in for a LOT more messing around (such as drive axels that need modified/replaced and such).

It also talks about some motor mount differences, sensor issues, modifying the 3400 Throttle Body with 3100 Throttle Body parts (so the linkages on the car still work right) and a lot more. It's a do-able swap if one does there homework. That is CERTAINLY a good document to start with for information.

Again, if the OP is doing it for performance, the 3800 is a MUCH better route.

 

Just for reference, you can use a tuner to change the Final Drive ratio, assuming the computer is supported by the tuner. If you look at the Wiki for the 4t60E and 4T65e, they have the same gear ratios, so the final drive should be all that is needed if you choose to swap. The 00+ impala and monte got the 3.4L with the 4t65e in it, and you could use the axles out of a 98-99 LTZ/Z34 for the 4T65e if you swapped it.

I believe that you can run the 3400 off the 3100 PCM as well, but I am not sure on that.

And I have to agree, if you are going for performance, the 3800 is the way to go.

 

A 3400 v6 will drop into a 99 Monte. I would keep the mounts from the 3100 though because the N-bodies had a side mount whereas the W-bodies don't. So keep the 3100 for misc. parts that you might end up needing and you should be set. A 3400 should work fine with a 3100 PCM. A tune will only make things better, but 3100's and 3400's are VERY similar with minor differences. It'll be a cheap 20hp gain and if you turbo it, you'll have fun.

Also, I might be wrong but I thought that the N-body cars had either 4T40E's or 4T45E's. I've not heard of them having a 4T65E's. It should still work fine though. It's a very popular swap with the 3100 guys.

 

Thank you for the replies everybody. This has been very helpful. The Monte only has 30k on the clock. I was trying to keep the tranny hopefully and just swap out to a larger motor and maybe have to just put in bigger injectors. I figured I could just reuse hopefully all the engine mounts and accessories.

I have noticed that the (98+ Buicks) the century only came in a 3.1 and the regal in a 3.8. I have seen none of them with a 3.4. The different transmission in the Grand Am's packing the 3.4 makes perfect sense. Are the 3.1's (96-99) as bad as the 3.4 about the head gaskets going bad and starting to leak antifreeze? I'm not really into swapping engine harness's and such. So I guess I'll be sticking with my 3.1 and doing the ported upper and lower intake swap to get some more power out if it. Thank you for all of the help folks! I'm new to this community but like it already!

 

Read the PDF link I added early on!! It actually tells you to use the 3100 harness and I believe recommends using the 3100 fuel injectors and the 3100 transmission. Honestly, the swap looks like it could be a cake walk (since the PDF is for a Grand Am 3100-to-3400 swap, you'll have to adapt a little to your application, such as the motor mounts Zipper mentioned).

As for head/intake gaskets, yes, I believe the 3100 AND 3400 both have that known fault. If I were going to do a motor swap, while it's out of the car, it would be VERY worth while to put new head and intake gaskets on (upgrade the intake gaskets to the aluminum ones and hopefully no more worries there). And head gaskets, hit or miss, I know people over 150K on factory head gaskets on those engines. Mine went bad at 180K.