I thought I'd stand up and say that the twin pipe system deserves more
credit than it's detractors give it.
Two years ago I added a supercharger to my TR6 and one of the last
modifications was the exhaust. The car is a 1975 that came from the factory
with the twin pipe set up. The supercharger can be disengaged so I tested
for back pressure with and without the blower. What surprised me most was
that the twin system only showed about 1 psi of back pressure and that was
AT REDLINE! It was another story with the blower at redline showing almost
9psi. The test was done on the road using a bung welded into the exhaust and
a tube connected to a 0-15psi boost gauge I could watch while driving. From
that test it appears to me that for a TR6 that has not been modified the
stock twin pipe set up is certainly adequate.
And some say they can feel the difference, well is it feel or hear the
difference? Are you so in tune with your car that you notice two or three
horsepower? Most everyone who's changed the exhaust likes a little rumble. I
know I'm certainly in that category. Ready to get some flames over those
thoughts!
I ended up building my own stainless system from 2.5" tubing. The original
twin manifold was port matched and generally cleaned up for optimum flow. A
new larger twin down pipe was fabricated that ended in a 2.5" flange. From
there back its all mandrel bent TIG welded 2.5" to a Dynomax Ultraflow
stainless muffler and a single 2.5" tail pipe. It's pretty darn loud
especially when running the blower although most LIST members like it. I do
let up when passing near a police officer. The Ultraflow is straight thru
and you could drop golf balls thru it so there isn't much restriction. And
back pressure has not been measured but other than open headers it couldn't
be much better.
Some things that I might do differently:
1) 2.5" pipe is really big and clearances very tight so 2.25" would be a
better fit
2) The Dynomax Ultraflow a bit loud for me
You can see a couple pictures at:
http://topshamautoparts.com/tr6/flange.jpg
http://topshamautoparts.com/tr6/muffler.jpg
My two cents for what it's worth,
Rick Patton
75 TR6sci
http://topshamautoparts.com/tr6/
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