Better exhaust setup??

[darvo]

2 1/4 is too small for a 325i. My car had a single 2 1/4 with resonator and I really felt the difference when I changed it to 2.5" single. Remember 325i's use twin 1 7/8" exhaust.

[CarsSuck]

Seriously 2 1/4" is whats on my dad's M10 car and it has great low end torque (relative to m10s). You need at least 2.5". 3" isn't hurting anything.

[blasphemy101]

Curious why there's a problem with a 3" exhaust. It's what I'm running on my other car.

[MattTHEe30GURU]

i just switched back to 2 1/4 and the 3in from axle back. i can definitely feel more torque now. i'm guessing more back pressure?? But i like it a lot better now

[blasphemy101]

i just switched back to 2 1/4 and the 3in from axle back. i can definitely feel more torque now. i'm guessing more back pressure?? But i like it a lot better now

"Back pressure" is not a positive thing; velocity can be, though.

Feeling "more torque" can also be caused by a greater DIFFERENCE in torque - e.g. midrange feels better because you have higher velocity (due to smaller pipe diameter) at 4500 RPM and also feels stronger because you're making less top end (because the decreased diameter leads to restriction as flow increases), so in the end you make more midrange COMPARED to your topend than you did before, but less power overall. I'm not saying this is what is happening, just food for thought.

I don't see the change making a HUGE difference, given many 2.0L 4 cyls make power with 3" exhausts. The header is responsible for the distribution of exhaust pulses, anything after is just a restriction - exhaust diameter is just a tool for managing that restriction (maintaining velocity vs. plugging). I don't see the M20, with .5L more displacement, requiring a smaller diameter exhaust (than the 2.0L motors) to maintain exhaust velocity.

[MattTHEe30GURU]

I also added a universal muffler right before the axle then after that 3in into the thrush muffler 3in out