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I found a Magnum 290 kit on ebay for my 09 yz250f; thought I'd give it a try. It was $400, figured that's not too bad for cylinder, piston, and gaskets. Advice #1: After you take your current piston off; put the new jug on with the water jacket dowel and the two steel dowels in place to make sure everything is going to fit right. Make sure the castings are perfect so it fits down nicely and flat. Mine were a bit too tight in one spot, and I had to dremel just a tiny bit off a steel dowel hole edge for a good fit. Advice #2: Be super careful about stuff dropping into the motor, take your time, cover the motor very well. Advice #3: The four head bolts? they are different lengths, note which goes where. Advice #4: Put the exhaust cam on first, then the intake. Advice #5: Measure your valve clearances as you take your motor apart. Otherwise you have to put it together again, just to see you would rather have shimmed. Advice #6: Put those metal clips into the cam caps, then put the cams into the caps (carefully getting the cams into the clip properly), then hold the cams as you put them in the head Power does seem to be increased everywhere. It's a noticeable increase. I had heard that it signs off hardcore up top; maybe I didn't rev the crap out of it because it was the break-in ride, but I didn't feel that. Is it a mini 450? Is it a 450 slayer? No, I mean, in the right hands it could be; but a 450 is still faster and even if you can be even with them for a stretch, then you have to shift. Mine doesn't feel as fast as a Husqvarna 350. It feels like a strong 250f, but still a 250f. Maybe now you can be one gear tall coming out of a corner, but not almost any gear tall like on a 450. The increase is noticeable and welcome though. It felt strong and I liked how it ran. I recommend this kit, it felt great.