1QwkSport2.5r "Last I checked, just about any oil that gets burned during combustion results in carbon and/or ash deposits. Kind of a given."
Yeah, methanol, nitro methane, and all oils are full of carbon atoms including silicone oils.
airraptor is one of the guys that warbird races the YS 80S and YS115WS. They both have dished pistons and allow high nitro. As Dave Schadel once told me, 30% ain't high nitro! 70% is high nitro. Rotor Rage 30% Heli is 100% synthetic oil.
If you are sputtering along at 5000 rpm, then a little carbon on the exhaust valve probably doesn't matter. I am running this engine in a helicopter at 12,000 hover and 14,000 idle up. A thin film of carbon effects the compression enough to make the engine sound ratty and give a noticeable drop in power presumably because the valve is not seating.