><< I was discussing the fact that I could now buy headers for my 6er with a
>guy from work, and he thought you need dual exhaust with headers. I was
>trying to explain that you don't want to open up the exhaust too much, and
>he
>didn't believe me, ok, but then he stymied me by saying the headers are
>there
>for exhaust (yeah), and what good are they if they dump back together into
>the cat? I don't really know. Will someone explain this to me please? I
>am
>ignorant.
> Flip
> >>
Flip,
Everyone seems to say "big is bad" but I think you're asking "Why?".
The idea with headers is that each tube be the same length (usually) and
this helps to scavenge the exhaust better as all of the exhaust oulses dont
hit the "collector" at the same time.
The idea here is to flow better by "clearing up the traffic jam" so to
speak. If four lanes could merge effiently into one, you'd move alot faster
right? Well, in theory it sounds nice but you'll never drive down the
highway and see four lanes merge into one. But if you increase from the
catback, you've effectly gone from one lane to two. Merging is alot easier
now eh? So now that we know whats going on, we have to see why we don't
want to make our exhaust into superhighways.
I know this is something I'm going to take a lot of flak on again but
here goes. With some types of fuel injection, fuel is sprayed on the back
of the intake valve when its closed. When the intake valve opens, the
piston is coming up on the exhaust stroke. Exhaust are being expelled out
the exhaust valves into your headers or manifolds to be on their merry way
into the atmosphere. BUT, since the intake valve is open, a little bit goes
into the intake manifold and mixes up the intake charge which has pretty
much puddled. Its now a good mix because of the exhaust. If your exhaust
scavenges to efficiently, it'll all just go out the exhaust valve and your
intake charge isn't well mixed. In addition to that, when the intake valve
opens, the charge will just flow right out the exhaust do to the valve
overlap that Rob talked about.
In summary, you don't want A LOT of backpressure, but you do need some.
The exception to this is turbo applications. You can run a 3" pipe on any
turbo application. Take a look at any deisel, you'll see what I mean.
-- Dave______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com
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