I did the test run of the "bean cut" reed today. It caused a LOSS of roughly 300 rpm and 1.3 lbs thrust! I went back to the solid reed, repeated the run and got the same performance data I had gotten before with that configuration.

So to summerize the reed test experiment: modifying the reed clamp gained about 60 rpm and 0.2 lbs thrust. Combining the reed clamp mod and the cut away reed lost 300 rpm and 1.3 lbs thrust. The conclusion is: modify the reed clamp and contour the reed to fit as close as possible to the seat, but do nothing else and you'll gain a little power.

Right now I'm at about 7220 rpm and 13.5 lbs thrust. That's with an APC 18x8W prop.

The engine configuration and mods are:

Newer style case with integral fan shroud, two runner per side transfer ports.
Two ring piston.
Long shaft crank with small counter weight.
Heavily chamfered and port matched-to-crankcase transfer ports. See photo in previous post.
Stock muffler with single 1/2" EMT exhaust pipe.
Reed valve stock except for slight bend in contour to match seat.
Reed valve retainer bent so that contact is only at base of reed.
9mm venturi Walbro carb.
C&H ignition set at 30 deg. BTDC

My next move is to get a bigger carb!

The speed and thrust of the motor is very dependant on the prop one uses, of course. When I set this motor up originally, almost a year ago, I had tried three different props, APC 18x8W; APC 18x6W; Master Airscrew 18x8 Classic. The APC props outperformed the MA prop. For the exact same motor conditions I got about 0.8 lbs more thrust with the 18x8W APC than with the MA 18x8 Classic prop, even though the MA prop was turning about 100 rpm faster. When comparing the two APC props they both delivered about the same thrust but the 18x6W turned 500 more rpm than did the 18x8W. I've heard that you don't want to turn a Ryobi much more than 7000 rpm static so I've stuck with the 18x8W APC. The APC prop is just more efficient than the MA prop, at least in the sizes I tested. My only complaint with the APC props is their weight, but all the nylon composit props are heavy. If I were really flush I'd get carbon fiber! I'll try wood first.

diceco