Rick, Joe:
Interesting comments on headers. I am still running the stock
manifold, but on my Z28 I installed Edelbrock headers (coated) and they
fit great, never leaked, and looked terrific.
As for the seemingly minimal power improvement, recall that
headers generate power 2 ways; reduced back pressure and scavenging.
Scavenging results from the partial vacuum applied to the exhaust port
by virtue of the inertia of a moving column of gas - the gas moves down
the tube and has enough momentum that it "pulls" additional gases out of
the cylinder.
Since the stock manifold has very low back pressure to start
with, the only benefit is from scavenging, in effect giving you only
half of the "typical" improvement from a header. At least, that is my
guess.
I would think that if one had a free flowing muffler and the
stock manifold, that they would have a pretty decent setup. I would
still expect a header to be better, but from your experience, it sounds
as though it is definitely diminishing returns. A racer would want it,
but for a daily driver it may not be such a good deal.
Great comments. Very informative.
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of Rick
Sent: April 24, 2006 8:20 PM
To: Mike Lunsford; 6pack
Subject: RE: Exhaust Manifold question
Mike,
I have to agree with Joe on this. Yes, the headers look cool but to me
they
are not worth it. They are noisy, hot, and almost always leak. Working
in an
auto parts store, I can't tell you how often someone comes in looking
for
thicker gaskets or two sets to double up to fix leaks. I'm sticking with
the
twin pipe cast manifold and adding a large single pipe system.
Last Fall I measured back pressure at the head pipes, below the manifold
on
the late twin pipe exhaust. Naturally my readings don't reflect pressure
backed up in the manifold but from the manifold back there was barely
1LB of
backpressure at 5,000rpm. The gauge didn't even start to move off the
pin
until 3500 rpm. Looks to me that the twin pipe system is pretty darn
efficient. I wonder if some of the noticeable power increase is more
from
the sweet sound rather than less backpressure?
Same set up running a supercharger at 9lbs of boost showed 9lbs of
backpressure. I still haven't redone the piping yet but have just
ordered a
2 1/2" Dynomax stainless muffler. Maybe next month's project.
Braced for flames-
Rick Patton
http://sidedrafttbi.com/index.htm
http://topshamautoparts.com/tr6/
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