so i just installed a 605 kit on my 73 500 four and i broke a ring after a month of searching i discovered alot of info my kit was a classic cycle kit and they happened to find me a couple of sets of rings so i got got that problem fixed. i think the entired thing all said and done cost about 600 bucks so not too bad. there was this company that had there hay day boring these guys out they told me that. the kit that classic cycle sells i cant remember the acually manufacturing company name. well the pistons are heavyier than stock so the best way to go is to have pistons made which runs 600 but you get lighter pistons and updated rings so you can get rplacements. also newer piston rings are thinner so they have less drag which we should all know less weight + less drag =more power. also they told me that the stock cam was they way to go they used to do some cam grinds but the 500 didnt improve much over boring it out. just some food for thought.
gotta disagree on the cam grinds, but it really depends on what you're going for. more bore will generally give you more low-end torque which translates to useable grunt around town. however; inceased breathing by a better cam or better yet, porting, will increase overall power quicker than the larger bore will. this is a pretty well-known fact with these engines. do a search on here for "650 cam in a 550." you can pick one of these up for really cheap and get some really cheap extra power.
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