exhaust size

[chrisyoung10]

What size pipe for an new exhaust do you all think I should use? I am planning on staying n/a until the warranty runs out and I was thinking around 2.5' but would like some input.

[mobomelter]

i think if you get too big you start to lose power with a n/a engine. i used 2.25 on my focus engine but i don't think 2.5 would hurt anything on the 3.

note: i'm only basing my comments on what i've learned from my focus and what i've heard.

[Matthew]

2.25 is what i had N/A then i went to 2.5 for turbo.

[goldwing2000]

On a n/a engine, making the exhaust any bigger then the intake is completely pointless and will actually detract from the performance.
In fact, a little smaller might be better because it would keep thinks flowing and allow the sysytem to stay at temperature.
If you have a huge exhaust, then you get hot spots and cold spots and the different air densities cause turbulent flow.

[RyanJayG]

I would go with a 2.5" for a Mazda3... simply because it will work fine for N/A but also not totally suck for FI... buy one exhaust instead of 2, you just wont be getting the optimum when you do go turbo.

[goldwing2000]

try here, too:

http://www.msprotege.com/forum/showthread.php?t=80207