OK ive posted about my old KE70'S Engine before but everyone calls BS everytime i do. It was a 4k block, bored 60thou (not sure if id be doing that on something running boost) Fully balanced rotating assembly, HUGE cam and quite a bit of compression, head, inlet, extractors were all ported to flow more and it spun to just over 10,000 RPM and absolutely flew. Made 74rwkw on the dyno but the operator wouldnt turn it past 7000 RPM lol.
This was built by a bloke who had 30+ years experiance building speedway motors and this one was originally in his sons KE70 speedway car. Built right they CAN rev hard but like anything once you start pushing the envelope itll shorten the motors life.
That motor lasted nearly 4 years and ended up just losing compression and never actuually died ( a mate still has it as far as i know). but i don't think with boost itd be the same story lol.