WWW.ROTARYENG.NET How to build a 250 HP RX8 P-port engine at 7500 RPM with welded in SS intake tubes. The SS tubes are welded directly to the steel rotor housing liner. My guess is it would be about 300 HP at 8500 RPM.
Yes he did notify me of the error after a a period of time but I did not feel it was worth correcting the data on youtube. 250 HP is probably no problem so I have been quoting that number lately. We got about that on a 13B p-port on the same dyno so I felt 250 HP at 7500 RPM was no problem for
an RX8 p-port engine with a 17% larger exhaust port area and a higher compression ratio. For aircraft use plus or minus 10 HP in a 250 HP engine is hardly noticeable as it will barely affect the top speed. You might be able to measure it in climb rate. The aircraft engine runs in a much narrower
RPM range than most car engines. HP below 7500 with a fixed pitch prop is of no interest. What one is more concerned with is fuel burn at cruise RPM's of 4500 to 6000 RPM. HP with a fixed pitch prop is way way down at those RPM's.
At $650 a day for dyno time I cannot afford to spend days tuning the engine to a fare thee well. Especially since all we had a was a Weber carb to work with which I felt was a bit on the small side. Also it is not possible to lean the Weber carb while the engine is running. The fuel burn and mixture ratio was all over the map indicating to me the Weber was not coping well with the tuned manifold. Air flows both in AND out of a carb with a tuned manifold. I will re run the test when I get the right aircraft carbs on there. For the fuel injection guys that is no problem as all you have to do is change the mixture look up table.
Perhaps this is not what one would want for a car race engine anyway. One should be interested in what it will put out at 11,000 RPM and the max torque RPM so one can change the gear ratios to suit. With enough gears in the gear box the range can be narrower. In a Formula One engine it is 17,00 to 19,000 as I recall.
I had no need to run a bunch of test with different length runners as I already
have that data from Mazda. We tried two different lengths on the 13B p-port to correlate the data with the Lemans engine data. It correlated well as we copied the Lemans tuning.
Dave was very impressed/concerned by the intense fuel column flow but I have seen that many times before starting in 1965 and I know the cause. It is a byproduct of any tuned manifold. Dave has limited experience with tuned p-port manifolds as that is not normally done on SCCA car race engines. In fact I invented the ram air box on the Chaparral 2D to contain it. All professional race cars now use ram air boxes when allowed by the rules.
Dave has never been a fan of p-port engines and they are outlawed in most SCCA racing classes. Jim Mederer of Racing Beat has said the same thing to me. The urban myth was p-ports were no good for street cars or road racing below 8,000 RPM. Mazda themselves proved that was not the case with the Lemans winning engine. So did the early Power Sport guys, Steve Beckham and Everett Hatch. Their p-port engine was tuned for about 6000 RPM and archived about 215 HP in later versions. It is all a matter of tuning the intake manifold correctly.
There is another factor and that is how the dyno is operated. Most car dyno operators do "sweeps". For aircraft engines that is not what we want. We want to see how much HP the engine will generate at a steady 7500 RPM and what is the fuel burn at reduced prop load at 5000 RPM. A prop dyno is better suited to aircraft operating conditions.
Paul Lamar ...No rotor no motor.
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