i just built my 421 cheetah 35pwks, SB cpi inframes , and my buddy has a 535 10mil cheetah, 39pwk's, BB cpi inframes. Both machines are animals but to build a "cheap" pv'ed motor get a 421, use a long rod 4mil crank and blaster 573 series pistons. Make a really well rounded machine, just keep those powervalves clean and it will keep you happy.