Michael, Stan:
If you are running the late model head and manifold, things are
flowing pretty efficiently. You can always get more from a good header,
since headers exploit the inertia of a moving column of gas to create a
very low pressure at the exhaust valve. This allows the exhaust gases to
exit more easily, and gives better filling of the cylinder.
But the stock exhaust manifold is pretty darn good in that it is
swept down with no sharp turns. Contrast it with the more traditional
"log style" cast iron manifold on older US V8s and you can see that the
TR engineers did their homework on manifold design.
Because of this, it probably makes financial sense to replace
the muffler before adding headers. The muffler is the biggest problem in
that the exhaust gasses exit through a handful of 1/16" holes.
Incredible that the car runs at all with that kind of design. Clearly a
case of cost winning out over engineering, and a quick inspection of the
inlet pipes on the muffler will make your stomach churn.
So, the bottle neck is the muffler. Not the pipes, not the
manifold, but the muffler. The problem is finding a GOOD muffler. Lots
of "performance" mufflers are actually miserable (but not as bad as the
stock muffler) and many of them get way too loud to suit people (the
Monza system is the frequent target of noise complaints, for example). A
system may in fact be efficient but if you can't stand to drive the car
because of noise, it really is a waste of time.
In the absence of a flow bench, all I can do is point to the
data that I have read, in particular data published by David Vizard (my
hero). He builds more motors in a month than we will build in a
lifetime, and he backs his claims with hard data. He is a consultant on
everything from cams to exhaust systems. He has designed cams for Kent
and Crane, for example.
The top three mufflers are, according to him (in order):
Cyclone Sonic Turbo
DynoMax Super Turbo
Walker Supreme Super "C"
There may be better ones out there, but these are the ones that
I have seen data on (admittedly, the data is now more than 10 years
old). He has rejected many because they don't flow, and many because
they don't muffle. For us, one that flows AND muffles is the hot ticket.
Cheers,
Vance
-----Original Message-----
From: 6pack-bounces+vance.navarrette=intel.com@autox.team.net
[mailto:6pack-bounces+vance.navarrette=intel.com@autox.team.net] On
Behalf Of Foster, Stan
Sent: January 02, 2008 3:58 PM
To: michael lunsford; 6pack@autox.team.net
Subject: Re: [6pack] Headers
<snip>
Re the headers, what I have read is that the standard late exhaust
manifold is
actually pretty good and the biggest bang for the buck is from replacing
the
two pipe system for a single larger pipe and especially getting rid of
the
standard muffler but I'll let Vance express his opinion on the muffler
since
he does it so well..
Stan
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