Hi Jeff
My friend had a 912 powered pusher seaplane that kept
breaking exhaust parts and threatened to lop off tail boom in the process.
He finally hacked off everything and just left fairly short straight
pipes. I don't think most anything you do that will allow reasonable flow
will make much of a noticeable difference in performance, some but not
tremendous. I am much more concerned with mixture with a modified exhaust,
MAKE SURE YOU ARE PREPARED TO CHECK AND TUNE WHERE YOU ARE NOT RUNNING
LEAN.Too rich is not too nice, but far better than too lean. Taint
towards a little rich at high power settings.
Of course you
could buy914 header pipes and turbo (along with
914airbox,carbs, enrichment solenoid and fuel pressure
regulator (perhaps ask Paul pretty please to sell you if he has)) and set
up a system to give you 100% rated power until the turbo can't keep up.
The turbo acts as a muffler when it is pressurizing, you could fabricate a
simple non restricting exhaust from turbo out, but you would probably be
best to stick with the beautiful 309SS muffler Rotax currently provides.
309SS is OK to wrap with header wrap BTW. Sticking with turbo normalized
mission will greatly simplify compared to the hocus pocus the TCU goes
through on a 914 to make the decision to make 115HP or 80HP. Even if your
mission was to turbo normalize, Iwould incorporate the enrichment
solenoid when the go fast lever is above 80% (could install a simple reed
or mechanical micro switch). Plumbing from turbo downwind is not as
critical as a 912/S, just restrict as little as you can and keep with an
acceptable noise level.
I talked to a friend who has an older
style Rotax exhaust on his 914 Xamango, he said it is susceptible to
breakage. He said if you get a goodbreak ina header pipe f,
the motor will quit. I don't fully understand, but it is worth mentioning
if you are designing an exhaust.
Good luck
Ron
Parigoris
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