Aleromod.com - My Exhaust

Quote:

Originally Posted by MixtapeMessiah (Post 257873)

but what you are saying is that exhuasts have no backpressure and thats not true one bit weither it be F/I or N/A, like you said a "HOT ROD MYTH" a myth that hasnt been proven because its not true, someone should sticky this one

Hmm..did I say that? Let's see:

Quote:

Originally Posted by Spilner521

Yes it's true that there is some backpressure in your exhaust. Even having a straight pipe out the side of the car will still give you a little backpressure. But you want to minimize it as much as possible. Having the straightest piping with the lowest restrictions and straight through mufflers will do this. Then you want to pick the right size piping to maintain exhaust velocity so that when valve overlap occurs, the velocity of the exhaust leaving the cylinder draws the intake mixture into the cylinder. This process is known as scavenging and is what allows an aftermarket exhaust system to help an engine produce more power and torque.

Here do this trick: Blow into a straw. Then pinch the end of the straw so that the opening is much smaller, creating backpressure. Then blow in it again. Which time was it easier to blow through?

No...looks like I'm not saying "exhausts have no backpressure". What I'm saying is that you want to minimize backpressure as much as possible, and what you're saying is that you need some backpressure to keep power. Like El_Diablo just said, when you have backpressure, it decreases both overall flow and velocity, both of them you want to maximize for maximum power production. Having too large of an exhaust pipe won't rob horsepower, it'll just shift the powerband higher in the rpm range. This will feel like a loss of low end torque, but you also have to realize that it will also gain more power up top. You need to find the right pipe size and use free flowing mufflers to maintain exhaust velocity and reduce backpressure as much as possible. This will allow the engine to retain it's low end torque as well as flow enough for maximum top end power.

Zero backpressure would be the best. Since we can't have zero, minimizing the backpressure as much as possible is the best thing to do.

As for the "hot rod myth", the myth is that you need backpressure to retain low end torque. It's been proven countless times on a dyno that no backpressure is the best and you want greater velocity to retain your low end torque. So in reality, this myth has been proven false many times.