Mike...this is an interesting subject. Exhaust gas flow is somewhat of a
"science" in itself. My disclaimer...I am NO expert on this...just an avid
reader on the subject. I have no doubt there IS an expert on this list
somewhere...
The 250 and the TR6 through 1971 had the single exhaust manifold /down
pipe/intermediate pipe all the way back to the muffler. Exiting the muffler
were two pipes. My 250's downpipe was 2" in diameter reducing to 1 3/4"
intermediate pipe.
I believe it was 72 when they went to the two-pipe manifold/down pipe system
with the two pipes running all the way to a single muffler. And 2 pipes again
exiting the muffler. I would venture to guess they were trying to improve
gas flow and arrive at optimum back pressure (and therefore horsepower) with
the two pipe system (all the way to again, a single muffler) perhaps in an
effort to deal with increasing emission requirements. I am sure there were
any number of aftermarket dual muffler systems available that probably
reduced backpressure somewhat and increased volume. The downside to
these...two to replace, extra weight, some like/some don't like the
additional exhaust volume (decibels, not flow)!
I contemplated what system I wanted to use, anticipating my engine would be
mildly modified for street use. I decided I would use the stock manifold and
a ss downpipe, intermediate pipe and ss muffler. The dimensions are 2" into 1
3/4." Single low-restriction muffler. After much reading on the subject I
don't think custom headers would make a BIG difference in horsepower if that
was the ONLY (no radical cam, no side-draft carbs, no high-compression forged
piston, etc.)modification you were making. All of the parts must complement
each other for optimal
performance/horsepower.
JMTCW...
Larry M
TR250 rising from the pieces in Colorado
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