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pre ignitions is where if you like to keep your sled on the lean side the top of the piston gets more carbon on it. sometimes this carbon can get hot enough it acts like a spark plug and ignites the fuel before its time. you can get a knock like detonation. in an old car this can cause the diesel effect when you shut them off.

detonation is where the engine is igniting the fuel from cylinder heat and compresion, but it is firing before tdc and thats where you get the knock.

on some of the new twins when you twin pipe them you have to buy heads also. the heads are a different dome for better flame travel and swirl. but also releave some squish.
on the polaris sleds you have a key switch to change from poor and high octane. but if you have ported or piped the sled and it says you have to run high octane the key swith no longer helps. the compresion is to high that the little bit of retard on the timing might not be enough and you will get detonation.

just a little food for thought.

nothing goes like three holes!!!!!!!
 

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or if you have a 2002 Yamaha SRX with DCS(detonation control system) you get to have that annoying light go off everytime you get that thing really really ripping. In case yall didn't know lots of people have it where when you really get on an SRX and it gets to a certain RPM range that thing kicks in. Not sure if they are actually detonating or whats going on but it happens.
 
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