Good morning BAX, Which of the series would be better for club pylon racing SF or FSR engines, and what is the defference between the two?

Thanks for your support!

It's impossible to say which engine would be "better". Likely neither, because they have been out of production and parts for them are very scarce.

However, it would depend upon the propeller used. The engines were originally designed as Pattern engines, and for different eras of Patter. The .61 FSR was usually flown with an 11 x 7 to 8 prop and turned in the high 12,000's. The .61 SF was usually flown with a 12 x 7 to 8 prop and turned in the 11,000's, though some people would use props like a 12 x 12 with a pipe and get the engine running at about 9,000 RPM, which was really too low for that engine.

The SF-series of engines were designed for lower RPM and lower noise. When the Pattern rules changed to allow larger engines, the type of engine went back to those similar to the FSR series. The FX series runs very well when propped to turn in the high 12,000's on the ground.

Fly your airplane and try different propellers to see which works best for your application.