I was starting to do some engine mods to my 1960 BT7 3000 MkI in early 90,s. The UK racers were here in the state for "the Healey Challenge". I asked them about the max engine bores and compression ratios and other engine mod criteria they could recommend. They bored their blocks +.125.
After my machine shop sonic wall tested the bores of my street engine block, I chickened out and only had it bored +.090. I used pop up high compression Venolia pistons on Carillo rods. I still enjoy it to date... have I had never a problem. it is a true 3 litre Healey now 3022CC, Danny