2.25 or 2.5 exhaust on my FC?
 

This is my street car so I need driveability. Which is a better choice. I want the best performance but I don't want to lose low end either. My car is an S5 so the the 6 ports accuation isn't a problem.
Charles

Exhaust narrative from Mazdatrix. They have done a lot of testing.

http://www.mazdatrix.com/e1.htm

FOr low end power, you want backpressure. SO 2.25. For ass kickin on the highway, you want as little backpressure as possible, so 2.5. I like highway racing, so I went 2.5 to a 3inch muffler. It all depends on what you want to do w/ your car.


When I get my TII, I'm commin over to Austin to cruise around wit ya man!!!

sweet rico. Sounds like a plan to me.
I wanna kick some ass all over the place.
:D
Charles

Header with 27" primaries collected into a 2.25" pipe, then gradually increase the diameter of the pipe each time you add components (cat, pre-silencers, mufflers, whatever).

If Mazdatrix knew that much their car would be setting records by now.

Chuck, you should just rip the muffler off of Brian's TII and run same size pipe. :gotrice:

Considering the primaries on my header are 2", and its an RB piece, I think that would answer your question. On a turbo car, the story is much different I think.

I just sold 2 N1's to a customer with an NA and enough 2.5" piping. I suggested 2.25" but he wanted 2.5". He also purchased a good quality Y pipe. Assuming the welding/fabbing is done well, how do you guys think this will affect its HP over(hopefully!) stock? The only other mod is an intake. One thing I know is it will sond and look great!

Also theoretically you could put a choke inline just before the Y pipe and tune the backpressure( and noise). Any objections to that statement?

When I say choke I mean butterfly valve and cable, like the one Arospeed manufactures. Sorry for the many posts in a row.

So will the 2.25 be better for my street car or should I go all out and do 2.5?
Charles

2.25 is better for the low end (in theory) but honestly, if you're keeping them separate, it probably won't make THAT much of a difference than 2.50 on the street. maybe on a dyno, but i doubt if you'll feel the difference on the street.

.02

So Evil,
You would go 2.25 from colector to cat, 2.5 from cat to Y and 3 to mufflers? Would that be a good set up?
Charles

The 2.25 to 2.5 to 3 would be good for a single exhaust. For a Y with dual exhaust, then I would keep the same diameter before and after the Y.

Using Pi R^2 you can calculate the diameters. With the stats below, you can see that dual 2.25" pipes are nearly 1 sq in larger than a single 3" pipe.

2.00" = 3.14 sq in
2.25" = 3.97 sq in
2.50" = 4.91 sq in
3.00" = 7.07 sq in