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Hey,
Have a '04 crf250r that I want to do a topend this winter. Saw some info that a 2008 piston gives a little boost. What would I need to do this? Just the 08 piston and '04 everything else?
Thanks

Welcome to the site !!

The physical piston should be the same , the only differences would be compression ratio ... however in my Service Manual , it shows the ring end gap to be one setting for 04-07 , then different for 08 , I can't say what significance that has with the 04 cylinder , my guess would be partly compression and allowing pressure and gasses to be pushed by , which would result in power loss ... how significant I can't say , but I would just measure the ring gap for your year rather than what 08 would use just to be safe , but I do not think there is any real difference in the cylinder itself or the piston size itself , with possibly the exception of a coating on the skirt of the piston maybe to lessen friction , and as mentioned , the compression is slightly different , with the 045 being 12.9:1 and the 08 being 13.0:1 , slight , but not dramatic difference

Thanks & thanks.

Just looking for a little punch out of the bottom but I can manage without. I just saw some saying they used the 08 topend with good results. I'm a woods rider so power out of slow tight turns with sand is nice to have.