Old OS61 SE pattern engine
 

I am using an old (very good condition) OS .61 SE long stroke pattern engine with Macs tuned pipe. Using 10% fuel and 11x11 prop. Contrary to what I expected the plane was fastest when using the 11x11. I am getting 11,450 rpm static. If I want to increase max speed should I look for a higher rpm setting of prop/pipe?
What is the highest and recommended nitro percentage? I tried YS20/20 and lost 300rpm.
Thanks a lot,
Ed

RE: Old OS61 SE pattern engine
 

Change your prop to an 11x7 or 12x6 You might try a 11x8, Try 15 % with 18% castor. RPM should be around 14 K you may need to adjust the lenght of your pipe.

Frank

RE: Old OS61 SE pattern engine
 

The O.S. long-stroke engines should be propped so that they turn in the mid-to-high 11,000's when leaned to just rich of peak RPM on the ground. Your engine sounds like it's running about the right RPM. They have been propped closer to 10,000 RPM for Pattern. A typical Pattern prop of that era was an APC 12 x 12 propeller. RPM would get into the mid-9,000's with a pipe.

To slow a model with the engine, you'll need a lower-pitched propeller. That means more diameter to keep the RPM in range. The long-stroke series of O.S. engines did not like higher RPM ranges, so keep it below 12,000 RPM, and you'll be OK.

RE: Old OS61 SE pattern engine
 

Thanks Bill.

Would you happen to have the power curves for this engine?

Thanks again,

Ed

RE: Old OS61 SE pattern engine
 

O.S. never released graphic information on their engines. We'd not have a power curve. In older magazines, the power curves you may have seen were made by the person who wrote the engine review. They did their own dyno testing.