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In a message dated 11/19/2003 1:53:08 PM Eastern Standard Time, msteitle@mail.utexas.edu writes:
Lynn,
Thanks for the very informative posting. Since we don't have to comply with SCCA rules & regs (i.e. restrictors in the intakes), my question is how does peripheral porting compare with the above in regards to hp & longevity. How fast do you have to spin the rotary to get good benefit from peripheral porting? (Powersport Aviation claims 215 hp from their pp engines.)
Thanks,
Mark S.
The periphery port is not only the obvious way to go, but is also the way most of the smaller rotaries were designed. Probably the side ports were a change made to reduce port overlap so the engine could be used in a street car with some tractability. Although a jumping jerking popping and banging street car with 300 HP would be fine for you and me, our wives wouldn't like it and the tree huggers would go off like a bomb.
The periphery port engine in the old car (84 body style) is a bit more tractable than the bridge ported engines used in the new car (95 body style). Comments to the contrary are not accurate. It will idle down slower than the bridgeported engines, but both are very unhappy about it. Back pressure from a poorly designed exhaust system would make a much bigger difference to a periphery port engine. Of course with the reduction unit up front the 2,000 RPM idle of the race engine is not even a factor. The periphery engine will idle down under 1,000 RPM and you wouldn't even need it that slow.
The periphery engine is what I would (will)? do. Paul Yaw has some great pictures on his web site about making the modification. His is all milling machine work and mine was all die grinder work. I epoxied in a piece of exhaust pipe tubing and left about an inch sticking out of the housing to connect the intake pipe on to it. The side ports are epoxied shut. So the intake is easy, just two tubes instead of four.
The 215 HP around 6,500 RPM figure is entirely believable. A 12A periphery engine could put out 310 HP at 10,000 RPM. Almost certainly there is some nut case out there right now with 04 rotors in a periphery 13B turning it higher on each pass just to see what can be, and cannot be done. Maybe 340 to 350 at 10,000 RPM? Probably. So what if it only has 300HP at 9,000 RPM? big deal. Would the RX-8 feel better with 300 HP rather than 230?
Could Tracy win again with 300 HP? maybe thinner wings, laminar flow?
So on a 20B that is just the aluminum housings being modified. So if you didn't like the 325 HP, you could put the stock housing back on and remove the epoxy from the side ports and go back to 250 to 270 HP.
I failed to point out that the airplane is a dynamometer. You make a change and watch the speed change. You correct everything to a sea level standard day using SAE charts for humidity, barometric pressure and temperature. You compare the results. You make another change.
Periphery ports are fine if you are confident that building a rotary is as simple as it really is. Fear not. Fire up that die grinder and get in there.
Even poorly done it's going to be over 200 HP.
Lynn E. Hanover
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