Nitro has double burn, the flame front is fast, butthen after theflam frontit burns slow (so slow it is still burning out of the exhaust pipe). Because of this and the very rich mixtures they use the race cars use a high advance at full throttle of about 60 degrees. And another reason for the twin plugs. But when you get the ratio below 1:1 or 50% nitro (not including oil) then the timing is similar to alcohol. But because of detonation with the leaner amounts of nito fuel mixture we use we need colder plugs and cannot use the high amount of advance.