"PVANDAL",
The dual branch exhaust is a bolt-on mod for a TR250 or early TR6,
according to the 6-tech manual. I have a later manifold that I just got back
from Jet-Hot that I intend to put on my TR250 when my exhaust gives up the
ghost. The intake manifolds are not interchangable, according to 6-tech. (I'm
assuming here that you're using an early, original head).
As the TR6 engine lost peak torque during its production run (about 25%
according to Bentley's specs) due to lower compression and other factors related
to emissions, the factory apparently held horsepower nearly constant by
improving "breathing". If you look at Bentley, you find the peak horsepower
comes at higher RPM on the later engines, and the peak torque is greatly
reduced. The dual branch manifold probably adds a smidgen of power at the top
end, when used in conjunction with the later cam (more overlap, duration, and
lift), later intake manifold (straighter shot), dual valve springs, etc. Just
bolting a dual-branch on an unmodified TR250 probably won't do much, since the
early 10-50-50-10 cam isn't conducive to revving to the kind of RPM where
exhaust restriction becomes a factor. Expect to have a harder time getting to
your starter with the dual exhaust.
Best Regards,
Tom Marincic
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