3500 UIM Question [Archive] - GrandAmGT.com Forum


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11-24-2012, 02:54 PM
So I noticed a few cars at my local wrecker have the LX9 3.5.

Just wondering if simply swapping the 3400 UIM for the 3500 UIM would have any benefits. Not looking for a racecar, just a bit more go.


11-24-2012, 03:10 PM
I haven't heard of anyone dyno testing just a straight up UIM swap, so it's hard to say with any certainty.

I'm of the opinion that on a mostly stock 3400 it probably won't do much. If you have enough mods for higher rpm air flow and power like headers, cam, larger TB, etc then it might help. The 3500 has larger displacement than the 3400 and uses a better exhaust manifold design and larger TB from the factory, so it moves more air and it would make sense that the UIM would help it make more power. The 3400 design has the runners start up on the sides so they are longer which is better for torque production, while the 3500 has a larger rectangle with more interior volume and the entrance to the runner is on the bottom making the runners shorter. This should produce more even cylinder filling and better top end power on an engine that has more displacement or moves more air. That's how the theory goes anyway. You'd have to dyno test it to prove it.

11-24-2012, 03:15 PM
My experience is as follows:
- Both UIMs with 65 mm tbs
- Both UIMs port and polished

The 3x00 UIM is better from idle to 2.5-3k rpm, after this it simply winds up. It is also louder/throatier.

The 3500 UIM does not make the torque as well, at 3k rpm it'll snap you into your seat better than the 3x00 UIM.. it's about equivalent to what the 3x00 one would wind up to torque/power wise but you get it from 3 grand and up. It also really moves well up top (highway passing in low gear, worse in 4th at 2k. This one is also quieter at getting the car moving.

Essentially, I feel that both make the same power, the longer runners on the 3x00 one allow it to move better down low. The 3500 one has a much larger plenum volume and will get into the peak power band sooner and stay there longer. I believe I didn't take as much of a low end torque hit as my phenolic spacers acted as pseudo runners...

11-24-2012, 07:41 PM
Yeah, if you have the phenolic spacers that will effectively lengthen the runners again a little bit while still having the larger plenum volume of the 3500 UIM.

11-24-2012, 09:51 PM
Alright then, Sticking with the stock UIM it is! Thanks for the replies guys!

11-26-2012, 07:45 AM
Yeah, I mean I personally liked it but it was a pain in the arse...
Between the MAP sensor, messing with the fuel rail (some say you don't have to, I tried for well over an hour to do it without messing with it... but no cigar).... vac line routing, etc...

I may go back to it at some point (my spacers were leaking, I didn't put gaskets on both ends like I should have so I went back to 3x00 one for a while).