Have yall heard that buz about the 3.9's having horrible back pressure with a one in 2 out exhaust setup?

 

My last Dakota was a 2003 SXT 3.9L and I had a single in single out Flowmaster 40 put on and by doing just that it did loose noticable low end I would think a dual out would be worse.....and by low end I mean stock I cold break loose my 265's from a dead stop after the change I got great sound but lost the ability to break them loose from a dead stop unless it was wet outside.

 

I would think typically a single out is better unless your running true duals with a h pipe. (But I also think that would require adding another o2 sensor somehow for it to run correctly...I may be wrong). I run a single on my 3.9s with a 2.5" pipe, high flow cat, and a slightly better flowing..yet not free flowing muffler. Anything over that is too much and you will loose your bottom end. I have learned this from thinking a 3 incher straight thru would kick ***. I was wrong. The bottom fell completely out and my dad would pull away from me every time in his stock 3.9. But I have 235-75-15s on my truck right now and I have no problem at all breakin them loose. Other then the exhaust, high flow intake, set of 8mm low ohm spark plug wires, platinum plugs, and running 89 octane pump gas instead of 87.....its bone stock.

 

im interested in the same question. im thinking about putting a flowmaster 40 series on my 3.9L. i would also like to go single in duals out if i could.

 

uhhhhhh did you read lil's post at all??????? I totally back her on that one. Ive had a couple trucks with 3.9s in them(even a 1 in and 2 out) sure it sounds great...thats about it. Your bottom end will fall out. I eventually swapped it back to a single in single out with a 2.5" pipe and my bottom end came back.

 

well do any of you know a way to run duals on a 3.9 and still be ok. what if u run a single in and single out but split the pipe to end up with duals that would work wouldnt it?

 

You want to run dual exhaust and still have your low-end power, run a proper pipe size, which just grabbing out of the air I'd say would be about 1.5" pipe. Somebody else can do the math, but 1.5-2" max is what I'd guess.

 

Most of the systems I have seen from different vendors offer 2 1/4" pipes. thats the one I had and it fell out. So prolly if you did go with a smaller diameter it would be fine.

 

When I had my V6 and ran duals I used 2inch and it ran fine.