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Engine basics => Engine set up tips => Topic started by: Dennis Toth on April 05, 2014, 11:56:42 AM
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Guys,
Got to the field today, it was a great day, light wind, slight clouds but the humidity was a bit higher. The engine run seemed to be a bit leaner than in the cooler weather.
Can anyone give some insight on how the humidity affects the engine run (4-2-4, 5% nitro, 27% 50/50, Fox 35 on 9x6 old Top Flite) and options to adjust?
Best, DennisT
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On the simple side, the higher the humidity, the higher the density altitude. Higher density altitude the less oxygen to make power. Just add more nitro% to compensate.
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Guys,
Got to the field today, it was a great day, light wind, slight clouds but the humidity was a bit higher. The engine run seemed to be a bit leaner than in the cooler weather.
Can anyone give some insight on how the humidity affects the engine run (4-2-4, 5% nitro, 27% 50/50, Fox 35 on 9x6 old Top Flite) and options to adjust?
Best, DennisT
Less power. More nitro.
Brett
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That's kinda what I thought.
Best, DennisT
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It's all to do with Relative Air Density (RAD).
Basically in warmer weather air pressure is lower with less oxygen in the air. 2-Strokes generally prefer cold, drizzly conditions (ask any classic 2-stroke motorcycle racer!).
This is down to a higher RAD, with more oxygen present. In these conditions your engine may run a tad rich so just screw the needle valve in 2-3 clicks. Vice versa in warmer conditions; make it slightly richer at the needle.
You shouldn't need more than 15% nitro for a standard setup.
See how you go on with this, it might also be worth going for a colder plug (no5-8 range) in warmer weather also.
Tim