When I had my Zetec rebuilt about 5 months back they bored .30 over and said that was the most they could do. Honestly I noticed a pretty big increase in power, but the reason it was rebuilt was the spark plug burnt a hole in the number 2 piston. Still can't figure out how all that happened! But back on point I think that had there been good compression (ie. no hole in the piston) then the power increase wouldn't have been that noticeable.
