jack

3" piping from the exhaust manifold. Empty catalytic converter. High flow V-Force© muffler. 3" piping to a 3" Y-pipe, into 3" tails and 2 stainless tips....any downfalls of big exhaust? I LOVE THE SOUND!!!

4RotorRocket

nice congrats man

Nan da yo!

The only downfall of big exhaust is if you have an NA. You need a certain amount of backpressure in order to maintain the optimal exhaust flow. The turbos already have that pressure thanks to the... well the turbo. But we NA fellas need the backpressure. I had the physics explained to me once, something about pulsation waves and how they cause turbulance and the smaller exhaust keeps the gasses on a strait path outside... or something like that. On turbos I dont think there is such a thing.

1Revvin7

Thats gotta be a t2. Its just too damn loud if thats an n/a.

j9fd3s

you dont want any back pressure, in fact if you can set it up right, you want vacuum on the exhaust ports

mazdaspeed7

Thats the biggest crock of **** I have ever heard.



Exhaust backpressure is never a good thing from a performance standpoint. People often confuse the high velocity of small pipes with backpressure. Exhaust gas velocity is what makes torque(and ultimately hp). Smaller pipes will have a higher velocity at a given rpm than larger pipes, but become more restrictive as the flow increases

Nan da yo!

Hm.... interesting. So under the entire rev range will the NA engine perform better with a 3 inch exhaust than say a 2 1/2? Is the reason why people use smaller exhausts for NAs is because they are quieter?



The guy that told me that also mentioned how its like putting your finger on the end of a hose and how the water leaves quicker from the hose even though its a smaller opening. Thanks for clearing that up for me.



BTW: Sorry for contributing to the mis-information of the internet.

TylerTRD

Um, a header to large…or piping to large in diameter is only going to make more power at high RPMs, and most of the time actually gives the motor a much smaller and narrower power band. In turn totally throwing off the cars balance. Its all about the velocity of the exhaust pulses. Bigger isn’t always better, unless this FC has some kind of crazy 1000hp 6 rotor sick *** motor!

boost_creep

HUH.

mazdaspeed7

Exactly. Like everything else int he world, its all about compromised. When you do anything, youre not necessarily making it better overall, you are shifting the compromised to better suit your wants and needs.



A smaller exhaust pipe will have a lower torque peak than a larger pipe. If you go too small, you make the powerband overly narrow because it becomes condensed. A small change in flow will have a greater effect on the smaller pipe because that same increase in flow encompasses a larger portion of the flow range of the smaller pipe. As the size increases, the torque peak becomes broader, and occurs at a higher rpm, but the peak torque will be lower.



All this is somewhat of an aside here though, because the headers are what really matter. Everything after the collector has a minimal effect on the powerband, provided the section after the collector can flow more than the section before the collector. There are other factors here, but theyre very complex, and have a smaller effect.



As a general rule of thumb, you want about .025"^2 of exhaust pipe area per hp. The RB headers have the primaries sized to right at 190 hp, which is about what a good full exhaust will put an otherwise stock car n/a.