I have a pipe bender here at the house but it only does 2 inch pipe. I didnt think that would be big enough, but then i was looking at the exhaust on mazdatrix and it was only 2 inches. Anyone have any opinions.

 

Mazdatrix RR says that anything bigger than 2inches would cause the car to lose lowend power for little high end. In other words not worth going bigger.

 

On a true dual that's fine, on a single exhaust you will want to go bigger.

 

A 2" pipe is perfect for a non-turbo RX-7. However, your tubing bender will kink the pipe and reduce the inside diameter, which will slightly reduce the flow rate (but not by a significant amount on a street car). If you want maximum flow, you should buy pre-formed mandrel bends and then cut and weld them to straight pipe to form your custom exhaust system.

 

But the bigger the pipe the better horsepower you get on a turbo right?

 

Not necessarily. I covered it before in another thread somewhere, but basically if you use to big of a pipe, the exhaust gas will cool too much before it's actually out and will thus be harder to remove, creating backpressure that you don't want. 3 inches is plenty on a stock turbo. I wouldn't personally go over 3.5 on an aftermarket turbo....

Back to the topic though...

I thought the ideal NA size was 2.5? I only ask because I don't know...

 

Usually. But generally speaking more exhaust flow is going to change your powerband, HP isn't everything, you don't want to gain HP but lose to much torque. Too big a pipe and you may lose to much low-end, not like we have any anyways right?

 

Thats just not true at all. On a turbo car you want the biggest exhaust system possible for all out performance.

 

No, because the exhaust gas stagnates in the pipe if the exhaust velocity is too low. Were there no limit to the "bigger is better" turbo exhaust theory, then you would see professional turbocharged race cars with 24" or larger exhaust pipes. Unfortunately, exhaust system design is very complex, and involves much more than just the pipe diameter.

 

Revvin, Meet the Evil Aviator.


IDEALLY... The best exhaust is an open turbo or downpipe...

 

Correct me if i'm wrong but i've been told by some that a little backpresure in a a turbo cars exhuast will actually help spool up

 

Backpressure never helps. Never.

 

aaron i hope that is a joke cause its been proven that backpressure helps low end torque....on n/a engines if you dont think thats the case. try running a straight header and compare it to a full exhaust. then get back at me

 

I've done that... car is loud and slow!

 

Here we go again...

Exhaust back pressure is NEVER good, exhaust velocity is what is important. Open headers shift the power band higher in the rev range due to the shorter length.

 

Backpressure never helps. Never.

Velocity helps always. Always.

 

+1

Fact trumps belief.

 

+1 for Aaron Cake

 

If I could, I would stick a hoover on the back of my GT35

 

Beat me to it.

The velocity is what's important, not the backpressure.

 

Aaron Cake > mightymite.

Just get a know good exhaust setup.

 

Spoken like a true genius

 

Boyaakasha!