Hi Scotty,
I am doing a big bore a10 engine at the moment so an interesting subject.
In my day job I re-design old engines to get more power and one of my hobbies that is in cooperated is "stretching" engines, In general I have found it worth every penny as torque always increases if nothing else is changed, but usually it is the start of something really good.
My engine will be either 777cc or 798cc depending on our final bore size of either 76 or 75mm, I am doing an 88mm stroke crank for it also. I considered 90mm but measuring up, this would have needed rather special steel rods in order to give crankcase clearance.
With a standard cast iron barrel I would not go larger than 72mm (without liners) as the blocks are terribly weak anyway. You can through bolt them as others have done but even then i think 72 would be marginal.
There are new blocks now available from I think Norvin, but I have not seen one and don't know if and where it has been improved.
I am having a complete new block made from billet 6061-T6 ally with much thicker walls etc and Ceramic coated instead of liners to give max strength and heat dissipation. Head bolt spacing will also need changing slightly as the bore is getting a little large for safety, even at 74mm.
Watch my build thread for updates soon.
Regards,
Julian
