2008 250 XCF-W convert to Thumper Racing 300 Big Bore. I took a brand new 250 XCF-W and broke it in. Then hammered it out in the mountains in Northern Arizona. The bike rode great (suspension a little jumpy) but no drama. Then took the cylinder apart and sent it in to Thumper Racing for the 300 Big Bore Kit. They bored the cylinder to a 300 and provided all the necessary parts to reassemble. After another short break in ride - the bike was taken to Colorado to do some serious trail riding. With the higher altitudes, it is not quite an apples to apples comparison, but the bike definately has more grunt and noticable power delivery throughout the whole powerband. My biggest concern was overheating. Other big bore 250Fs that I have ridden with had trouble overheating - not this one! Roots, rocks, step ups, hills - no problem. No leaks or any other problems to report at this time. I will post more info as time goes on. Right now the suspension is off the bike getting redone, so after that, I will keep you posted!