Originally Posted by
Hydro Junkie
To take this a little further, HighPlains' post is very informative but he missed one little detail that most don't think about. When he said lowering the nitro is like richening the needle, he is 100% correct. The reason for this is that when you add nitro, you remove fuel from the mix. Nitro is an oxidizer, meaning it adds additional oxygen to the combustion process. The effect is like turbocharging a car engine, more oxygen=more power, but at a price. To make use of the additional oxygen, you need more fuel to go with it. Not having enough fuel results in running lean, subjecting the engine to early detonation and higher than optimum heat levels. In your full sized car, this would sound like "knocking". This, just like in a nitro motor, robs power and damages parts. Since I run 50% nitro in my boats, the effect is even more pronounced. I have a marine .67 engine that has a badly pitted head and piston due to detonation, caused by a different issue. Regardless, the general rule of thumb is when you increase nitro, you richen the needles
Excellent "insider" information most people aren't exposed to. There is a lot about nitro that isn't common knowledge and seems backward.
Nitro produces less heat than alcohol, which is what it replaces. So the more nitro in the mix the less btu's. So you can make a case for higher nitro fuel burning cooler. And since you usually don't need more oxygen in colder months, the case can be made also that if you're flying in the winter, lower nitro fuel just might run better as it'll put more heat into the engine and the lessened oxygen won't be missed. That of course, should consider what you're actually doing, putting around for fun or racing flat out for blood.
There is also the affect the nitro has on the engine timing. Yup... timing. There are no timing adjustments in our glow engines is there? Well, yes. The fuel mix affects how soon ignition starts in the cycle. And nitro affects that.
Good thing about all this, is almost nobody is running pylon nowadays, or any other "needle critical" glow engines. However, I do notice that running 5% in the winter and 15% in the dead of summer seems to work for my present fleet. In fact, I have a model/engine combination that seemed to be having cooling issues a couple of years back when it was brand new. I noticed I was still running my "winter fuel", the 5% stuff. Switched to the 15% and the sucker ran better. I still made some of the cowling louvers functional (directly behind the cylinder).
Was it the BTUs? or the timing? or the better cooling?