I have a stock 250R cylinder with a 310 L.A. Sleeve in it. It's freshly borded 1 over. A guy is trading me a Cool Head for my Pro-X head and I need to know what size cc dome to put in it. I run race gas but don't want real high compression. Can you run the same size ones a stock 250R does or is there big bore domes?

 

Make sure that the ProX head will fit your jug. The head on my 310 cylinder would not fit on a stock jug. Otherwise just call up ESR and tell them what you want. They are very helpful and can give you all the info you need.