Rc Fuel Faq
Hobby Bob:
Thank you for the info regarding the pressure line, maybe this can be put to rest since that sounds like a reasonable answer.
Why can higher nitro percentages run cooler than lower you ask?
-When higher percentages of nitro are used (assuming that the oil contents are identical), the needle must be richer than lower nitro content fuels. With a richer needle setting, more fuel is consumed which means more oil, methanol, and nitro is run through the engine. Methanol has a very dramatic cooling effect when run through our engines, nitro has a fairly good cooling effect and the additional oil does not hurt either.
The most probable reason that your engine ran fine without needle changes when you moved from the 10% to the 20% is that you were too rich on the 10% in an effort to reduce the operating tempreture.
When you were hitting 300 degrees, how was the engine running?, You should not have a problem running at higher temps if it is not too lean. For instance, while testing a new car engine coming out on the market soon, we saw some high operating temps, well above 300 degrees, and we were still rather rich. When properly tuned, we saw mid 300's on gallon after gallon and running it as hard as we could, nearly non stop as long as the batteries would hold out. This engine was tortured, as hard as any driver could and it never flamed out or overheated or was run lean. An abundance of power was always present. After a lot of fuel (gallons, not tanks), the engine still had like new compression! We did not even change the glow plug once. On a few runs using a traditional high oil airplane fuel, we recorded temps over 400 degrees and was still putting out power without being lean. The moral to the story is that you should tune your engine to where the mixture (high and low speed) is set according to the conditions encountered (fuel, altitude, gear ratios, air temps, etc..) without setting it lean. Heat makes horsepower as long as heat is not caused by over lean mixture settings. If you did not have a temp gun, you would have tuned your engine according to the conditions and may have never noticed that it was running higher than what some folks consider normal.
As far as why your engine ran the way it did on the 10% fuel you mention- I can not give you a definate answer on that, a lot of variables are involved that would prevent me from being able to get specific. If you want to shoot me an e-mail with some specifics, I will do my best to answer your question.