An interesting topic...also discussed by none other than Kas Kastner in his
original treatsie on Triumphs entitled "Competition Preparation Manual" circa
1968...pgs. 21-22.
His conclusion was the stock cast iron exhaust manifold was fine for street
use and suggested doing port matching.
He also concluded that the stock manifold would give "slight power increase"
over the tubular racing version at low revs. In addition the tube type header
would increase underhood temps and noise.
They tested numerous variations on exhaust pipes and concluded the best
solution was a single 2 1/2" O.D. SINGLE pipe running the length of the car. Of
course without mufflers in all cases.
Another finding was that any two pipe system always resulted in a power loss
of "at least 8 horsepower."
What effect mufflers (any) has on this system seems to left open to
conjecture. He did not do any tests with alternate mufflers or systems for the
street
versions.
Fast forward to 2003 and his updated "Triumph Preparation Handbook" in which
Mr. Kastner states...."Fitting a steel tube exhaust header system is of great
benefit. Especially when you have also upgraded your camshaft to a longer
duration and overlap part."
An interesting topic....
Larry M
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