how much should i expect to pay to have my cylinder head modded, i.e bigger valves, ported & polished, machined for double valve springs etc?

 

Unless you are going for monster power (600hp+) std valve size will do. A top notch porting job will cost Ł1000-Ł1500 with cams/springs.

 

cheers cam, am looking to achieve 600+. may as well do it all at once

 

Best plan is to start with a brand new head casting then IMO. GGR have been selling off some on eBay recently.
Karl Norris did a 600+hp porting job for me on a new head casting and the quality of the jworkmanship was incredible.

Cam