Originally Posted by
SushiHunter
Is there any truth to that?
in a word, nope.
the 'break in' period is to allow the piston ring (if any) to 'seat' or 'wear in' and to allow any metal to metal moving parts to wear in, any left over metal flashing or casting leftovers will wear away.
once the engine is broken in, changing the fuel does not make the engine need to be broken in again.
(although Jester did make a very good point... going to a higher nitro content will cause an engine to run 'more lean' unless you adjust the needle valves to suit the new nitro percentage)
it's sort of like breaking in a new pair of shoes... once they're broken in, changing your socks doesn't make the shoes need to be broken in again