I know the feeling, well not quite in the same proportion but the same happend to me after a rebuild everything on the motor seems fine but once up into the higher revs it starts to get flat and burns oil. My only thoughts were the bores.
To be honest I was going to just go to K20 had really considered a B20 but would have gone K in the end. If my JRSC setup on a rebuilt bottom end goes bang then Im just going to go K20 as it probably just the Ideal option.
Is a proper shitter seeing as your build was to such a high standard and kind of a bench mark for UK B18's
Steven, i followed weiseco specs for the ring gaps, and have two dead pistons sitting here. There gaps etc are abit tight.
As Rich has said get another block and a set of rings. Theres way to much time and effort gone into this just to just sell up.
Ive been in your shoes, im on my 2nd forged engine. I seriously thought about selling up the turbo at the time, then thought