CRrider125r said:
What is detonation?
What do you mean this pipe will cause this?
Because i bought an 01 cr125 with this pipe on it .
detonation is when the fuel air mixture ignites in the cylinder before the spark plug sparks. the fuel ignites because of the pressure in the cylinder is too high for the octane rating of your gas. the opposing flame fronts (from the spark plug and the detonation) collide and put stress on your engine. what is meant by the pipe causing this condition is that the pipe is more constrictive and puts backpressure on the engine. that pipe may not cause pinging with you're particular bike, modifications, and atmospheric conditions, though.
about the altitude, your going to run richer because the air is thinner.
i know that at this altitude the motor has less compression
compression is the cause of detonation so i would say the altitude is on your side. i have a yz250 w/ and sst pipe and so far it runs good (i do not use race gas, just premium @ the pump).
here is more on octane rating and some on detonation
http://auto.howstuffworks.com/question90.htm the article says four stroke, but the principles still apply.