Looks like bore/stroke from the later model 250R was 62mm x 41.2mm with 11.6:1 compression. The 300 is listed as 62mm x 49mm with 10.6:1 compression (supposedly lower so it will run on 86 octane pump gas). So I'm wondering if a set of 250R race pistons from Wiseco at 12.5:1 compression will work on the 300 engine? I haven't taken it apart yet to see how the combustion chamber looks compared to the 250R, but hoping it might work to get a high-comp racing piston setup for the 300? Also a 2mm and 4mm overbore piston is available for the 250R, can we do the same with the 300? Anyone done any internal engine mods at all on a 300 yet? I haven't found anything by looking around yet, but I'm willing to try it if no one else has.

I don't think there's enough cylinder wall clearance to allow for any (much) overbore.

Supposedly the cylinders are the same as the 250R, so should allow +2mm or +4mm?? However, the Wiseco rep told me that the pistons from the 250 won't work on the 300 but they'll make 300 pistons if I send them one of mine to use for the design. So that's the plan, but I won't be able to tear it down until our track day season is over in October. If anyone else has a 300 piston available sooner, let me know and we can get it over to Wiseco to start making the kits!

same diameter but the lining is different

same diameter but the lining is different

Ok, thanks, I guess we'll see what's possible after taking it apart. Worst case we'll have to stick with the stock bore and just go with high compression pistons and get the heads ported.