More importantly it wont be a restriction when you start pumping more air through the motor allowing more HP to be gained from mods.

Well I just picked up my front ported manifold. Hopefully gonna bolt it on tommorow. Only cost me $40, its my first step. Next will be headers. After a cam that is

40 dollars..wow..nice deal there! defintally do let us know on how it all goes!

I think i read this almost word for word somewhere...

I just typed it myself. I'm on [H]ard Forums a lot, and there was a huge debate about exhaust that spawned off of the "ricer cold air intake" thread.

If anyone wants to know what a good exhaust is, click the link in Rogue'* signature for his Mod List. He'* the second fastest Bonneville here, and hasn't made major changes. Please note that he'* also running a catalytic converter

There is an important difference between tuning your exhaust for drag racing and driving a car on the street.

If your only concern is the quickest WOT run you can do...then go for open headers. If you have any interest in part throttle response you're going to want exhaust pipes.

The idea is to maximise the velocity of the exhaust. As the gases cool they contract. Having a slight restriction in the form of a smaller diameter helps maintain the velocity although it does add slight backpressure. Of course we're not seeking backpressure...what we're looking for is velocity...backpressure is a byproduct.

If you have backpressure as the result of a restiction (GP U-bend for example) it'* not going to help you at all...it will hurt you.

By maintaining the highest possible velocity, and therefore having slight backpressure (1 to 1.5 psi), then we would have an exhaust pulse with a median velocity at its centre, a higher velocity on the leading edge and a slower velocity at the trailing edge. The lower velocity at the trailing edge will help draw the next exhaust pulse down the pipe...or scavenge.

The primary pipe diameter and length play a big part in determining your power band. As well, the diameter and length of the collector will play an equaly big part in determining the rpm range in which the exhaust is best at scavenging and best at being unrestrictive.

The longer your collector, in general and assuming a reasonably sized piep, the more your power band will be skewed towards low rpm power and conversly the shorter the collector the higher in the rpm range will be the peak exhaust efficiency.

As above, the exhaust diameter plays a big part in the velocity of the gases, all the more so as they contract while cooling.

While at the track with open headers, you'll loose a bit in the lower rpms versus a closed exhaust (assuming it'* reasonably well sized) but you'll more than make that up in the higher rpm range.

For those that have driven their cars to the exhaust shop with open headers will surely know how unresponsive the car is on the street in that configuration.

My $0.02...

Cheers,

Good points Foghorn, you are correct, the tricky parts of exhaust theory are heat and expansion issues.

Rogue has headers, they're pretty, and very complex. and a high flow cat. Both are for high flow, meaning his mufflers are the highest restriction, however he wants a quiet sleeper.

All of the exhaust theories are true, but we do have to remember that we need more power in order to benefit from running open headers. Cutouts are an effective way of running open headers on the track.