The engine is a new OS 91 FX with about a quart through for break in.
The engine started fine but needed the electric. I tried to back flip the prop to start but no hint of life. Glow plug is a OS #8 for the numbers. A fox standard long was tried and added a few hundred rpms but idle suffered a bit so it was not used in the test.

The stock muffler’s baffle was not removed. For the tuned pipe I used a Macs 11cc muffled marine (#1369) because it’s what I had on hand. It’s a bit small on paper however I believe it was the optimum pipe. The header ended up 3 ¾” long from the cut to the flange face measured down the tubes centerline.
The props are the dark grey Master Airscrew S-2 series formally known as Scimitar type.
Power Master 15% nitro 18% oil was used. Power Master FAI fuel was tested and the numbers were down only 150 rpms from what you see below and the reliable idle speed had to be raised from 2000 to 2100 rpms. Fuel usage was very low, but lets face it the power output is pathetic.

Throttle response was surprisingly lightning fast with the pipe no flat spots no loading up at any throttle position. The throttle position is the most sensitive I’ve come across with the 13750 rpm test, just close the throttle ever so slightly and the rpm drops, this leaves me to believe that that carb is the primary rpm limiting factor of perhaps many others. This engine is rated at 2.8 hp@15000 so in further test I will reduce the prop load to TRY to get this engine to 15k and find the true power at this rpm, muffled and piped.

The engine was peeked just long enough to get the reading than richened and allowed to cool at part throttle.
Air temp 75* Humidity 50%


Prop…………Exhaust………....RPM…...Hp… …Pitch speed mph…. Thrust lbs.
12X 8……….Stock Muff ……11500….1.28……….87.12……………. .8.9
12X 8……….Tuned Pipe……13750…..2.11………104.17………� �…12.5
13X 8………..Stock Muff……10700….1.38………81.06…………� ��. 9.18
13X 8……….Tuned Pipe…….12500….2.19……….94.7………… ……12.5