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Doug,
About the two VS one piece manifold flange.
The reason for the RB single flange is to prevent fatigue failure of the studs
in the rotor housings. The block of course is very rigid and does not
move. Expansion and contraction of the header from thermal
cycling can eventually break the studs off. First it will
crack the exhaust/welds, if you keep making the header stronger
to the point where it no longer fails, it will break the studs off. A lot
depends on how the header is made. The worst case scenario is a Log
type manifold with short stubs to the rotor housings and two
separate flanges. The short stiff header has very little flex and
will place a load on the studs. If you have nice long looping header
primaries, there is enough flex in them to absorb the expansion and
contraction without damage to anything. The best bet is to make sure things
can move around a bit. If you use a log manifold, put a slip joint between
rotors etc. Then you can use two separate flanges without any
problems.
Monty
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