Headers Real or mythical hp?

[CO996C4]

<_< Well does anyone really think these exhaust mods and more specifically headers, really make the effort and cost worth it over stock manifolds? Loren what do they make the exhaust manifolds out of? Does it differ for MY? Are they "tuned" like aftermarket claim to be?

[JimB]

All headers and exhaust manifolds are tuned. They are just tuned for different purposes. A simplistic explanation would be that when one cylinder releases it's exhaust it sends a burst of air down the exhaust tube. Behind that burst is a vacuum. The trick is to have the next cylinder that fires (on that bank) send it's burst of exhaust into that vacuum at the point where the tubes meet. The vacuum sucks the next burst therefore making the engine more efficient. The length of the header tubes are used to time the arrival of the second burst just behind the first.

Obviously, the exhaust bursts will come at different intervals at different RPMs. That is why different headers are "tuned" to maximize power at different RPMs. That is also why you can really mess up your engine by doing it wrong. If you think it through, it also becomes obvious why you can mess up torque by reducing backpressure. Reducing backpressure allows your first burst to travel faster potentially robbing your second burst of the vacuum advantage. Blah blah.

I realize this is a greatly over simplified explanation but hopefully it helps.

As for are they worth it. They are if the hearders are carefully matched to your engine, it's modifications and your driving. I would certainly educate myself on how they work and then ask a few thousand questions before I bought a set. It's unlikely that you will see much advantage over the stock units on the street.

Jim

[CO996C4]

:cheers: Thanks very much Jim I like to drive fast but not for prolonged periods like racing I will apply money in more cost effective modifications for street use.

I really like this forum as it is quickly educating me on my new 996!

[nova996]

Jim, Thanks for this explanation. I never really understood that before. But I know on my M3 I kept the stock exhaust because I kept hearing it had an optimal amount of backpressure to it. And that aftermarket exhausts very often had too little backpressure which reduced torque at lower RPMs. Not it makes sense.

Edited January 6, 2004 by nova996