RCU Forums - View Single Post - cc to flying weight? & what prop?

04-30-2006 | 08:50 AM

#20

BillS

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From: Greensboro, NC

RE: cc to flying weight? & what prop?

Quote:

ORIGINAL: go-vertical

Thanks Bills... THe 2 times the weight to cc seems like a good starting point. What about prop size? what rule of thumb do you use to determine what prop, 16, 18, etc. Are you looking for one to turn a specific rpm range?

Reading the results of a search for Ryobi in ‘Engine Conversions’ or ‘Tachometer Readings’ will give yield a wide range of props. The prop sizes mentioned are the most common sizes used on 25 and 31 engines.

I measure the RPM in the original blower or weed eater installation (electronic tack). The measured RPM is assumed to be the design speed the engine. Then I attempt to prop for the design speed. A Ryobi trimmer will turn 8,000 RPM. The MB 290 25cc blower also turns 7500/8000 RPM depending upon Hi needle setting. Stihl blowers are set to turn 8000 when they are sold.

Bill

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