7650 with a 16x10 apc. Just lightened flywheel and larger carb and aluminum jag muff.I also like to remove the block to cylinder gasket and replace it with rtv . This increases compression by bringing the cylinder approx. 27 thousands closer to block

27 May 03
Ryobi 31 2 ring piston; turned flywheel; reed valve stop .125"; electric junction box muffler; run time less than 1gallon fuel
Dyna Thrust 18-8 5940
MAS Classic Blk 16-8 6600
APC 16-8 7620

disassembled cleaned all screw holes and bolts, made .005" brass exhaust gasket. LOCKTITE everything.

Hi guy's;

I have a Ryobi 26cc and get the following with mod. muffler, stock flywheel, larger carb and enlarged ports.

18x8 ma. 6900 - 7000rpms
18x6 ma. 7440rpms
17x8 apc. 7290rpms
16x8 apc. 7800rpms
16x6 apc. 8000rpms

16x10 zing. 6700rpms
16x8 zing. 7200rpms

I have done two conversions now this one and a Stihl 54cc.
so I am no expert. But both engines do not like zingers. I don't listen to hype about diff. props, I just go by results. I have put a fish scale on the ryobi and all the thrust dropped when using zingers. Down to 9.3lbs with the 16x10.

I now fly the 18x8 ma. on a 14 - 15 lbs clipped wing cub and before I installed the TME. smoke kit, she would hang on the prop for 5 - 8 seconds. Just a tad more hp. and I could hover . I tried other props too but got tired of typing . Hope this helps.

Peter

I tacked a new box stock Ryobi 31cc string trimmer with straight shaft and got 8100/8200 RPM. Nothing was disassembled or touched not even the carb adjustments. The test was no load except string in the trimmer head.

Eventually every prop imaginable will be tested. I may reassemble the other engine back to box stock and check the RPM. Do you know the RPM of maximum torque? Does the magneto limit the RPM?

My ...had forgotten this thread..
Same engine as above w/ older style head, Walbro 167 carb, CH Ign
APC 16-10 prop, different DIM exhaust deflector : 8350 rpm
APC 16-8 prop " " " " 8950-9100 rpm

A torque curve would be nice.

With no load (string head off) a stock Ryobi 31 cc engine will tack 11,000 RPM rather easily. I stopped at 11.000 but it would have gone further. No RPM limiter exists on this engine. It might be a candidate for a pipe. Now I really wonder what the torque curve looks like.