Mike:
There is no doubt that a header will make more power than a
stock manifold, all other things being equal. The stock manifold flows
very well, but does not deliver the scavenging of a header tube with its
resulting gas inertia. Having said that, the manifold is cheap, won't
rot the way headers can, and it is very quiet. If you bead blast it and
give it a couple of coats of header paint from a rattle can, it looks
amazingly good, too.
The biggest bang for the buck on the exhaust side is to get rid
of the stock muffler. It is amazing the engine even runs with the
Leyland muffler, given it has a cross sectional flow area little better
than a soda straw. I have concluded that this is why the dual exhaust on
the TR6 is a performance upgrade over the single; not because the cross
sectional area of two pipes is better (the single vs. dual pipe area is
surprisingly close), rather it is because the dual inlets on the muffler
double the cross sectional area into the muffler (from 0.1 square inches
to 0.2 square inches - hah!).
Unfortunately, many of the "performance" mufflers out there
either don't muffle, or don't flow so simply tossing the stock muffler
in favor of another brand is a crap shoot. You need good hard data to
know which ones work and the manufacturers are not forthcoming with that
data as a rule. The only data I have seen (from David Vizard) shows that
Cyclone Sonic Turbos, DynoMax Turbos, or Walker Supreme mufflers are
good at both noise management and flow. You should be able to find a
custom exhaust shop that carries one of these under "mufflers" in the
yellow pages.
After you have replaced the muffler with a free flowing exhaust
system, if you still want more, a header makes sense. Jet hot coating
(inside AND outside) of a header is a good idea, and will keep heat soak
to a minimum as well as make it look terrific and stop rust.
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of michael lunsford
Sent: April 24, 2006 8:05 AM
To: 6pack@autox.team.net
Subject: Exhaust Manifold question
I am nearing the point where I will be yanking my old cast iron original
type exhaust manifold off of my old motor to get it jet hot/powder
coated. I have the late model exhaust manifold with two holes for the
down pipes and have had the ports matched and smoothed for what I
believe to be about as good as you can get with the stock cast iron
exhaust manifold.
I have seen on this site and in several of the "how to" books comments
to the effect that the stock 2 hole exhaust manifold is prettty good as
it is. I have also seen comments on this site about people having
problems getting the aftermarket headers to fit properly and the need to
have them jet hot coated. With the extra cost and fitting issues
considered I am inclined to use the stock exhaust manifold with free
flow exhaust pipes thereafter but would like to hear what those of you
who have been there/done that have to say before I begin this part of my
rebuild project.
Mike Lunsford, 1970 TR 6
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