the bottom end of ka's are pretty strong believe it or not. the only thing that makes them horrible for lots of boost is the head and the sr has it draw backs also. for instance sr bottom ends are weak. and those 500-600 hp srs w/ stock bottoms are dyno queens. but the heads on sr's can handle lots of boost. so either way youre gonna be set back, but overall sr's are better for more boost = good track engine. but on the road you dont really wanna boost more than 8-10. why? because the more boost the more gas the more money to spend. so ka's = good street engine