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SPE 40cc question

Old 05-12-2016, 04:48 AM
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Default SPE 40cc question

Bought a used SPE 40cc engine. It starts and runs fine except the RPM's don't seem to be high enough. Looking at the manual it says use a 20x10 or 21x8 prop and a 6V for the ignition. Then on the last page in the specifications it says use a 18x8-22x6 prop and a 4.8V battery for the ignition. Maximum RPM 9000 and Idle RPM 1300. can anyone straighten me out on this. Thanks
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Old 05-12-2016, 06:18 AM
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Something you are going to have to sort out, think I would start in the 18-19 in. range. Remember most engines are rated by their makers as turning out more RPMs and HP than they actually do. This is true with almost all
engines from as far back as I can remember(thats going away fast). Some depends on if it's tuned right and broken-in?
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Old 05-14-2016, 08:05 AM
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The 18X8 or 18x10 should be the better choice. 20 and 22 inch props are getting on the high end for a 40cc engine. RPM's with the 18" props will be in the 7000 range plus or minus. 9000 is very optimistic. The ignition voltage depends on what the module you have was designed for. If it's very old, probably a 4 cell pack. Only in the past 3 or 4 years have ignitions been designed to use lipos and higher voltages. It should say on the module, or at least search for the brands website and get more info. Regardless, that won't affect the rpm. Prop size and tuning do that.
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