[HarroMoto]

I'm looking at putting a big bore kit in my 2008 crf250r........have looked at several options

1. eric Gore 262cc

2. Thumper Racing 270

3. Athena 280cc

does anyone have experience with these products?

Are they worthwhile?
Are they reliable?
What jetting changes are required?
Do they require case mods or are they bolt-ons?[/b]

[RedRaider]

I put a Thumper Racing 270 kit on my '04. It is very simple to install and relatively inexpensive . Since it is a modified stock cylinder, no case machining is required. It also solves the weak cylinder issue with the stock '04. The kit comes with recommended jets (richer). The engine is a good bit stronger from low to mid range and will pull out of corners in a higher gear so less shifting is required. Of course it still doesn't have the arm-pulling torque of a 450 but the bike is easier and much more fun to ride. With its light weight and great handling, it is now perfect for offroad racing. I've been racing it in GPs for about a year and have had no problems except slightly higher initial oil consumption. I expect that it will be at least as reliable as stock and the valves are likely to last longer since you can ride it at lower RPMs. The only issue that I can imagine is that the ductile iron liner isn't as hard as nickasil so it may eventually wear out. I don't see this as a problem since replacing the liner is relatively cheap.