a dx bottom and a si bottom are practically the same thing, you won't get any gains at all really. you'd be better off finding a nice z6 or y8 head and do that swap if you want some cheap easy power gains. the real question is, are you doing this in a dx or a si? if it's a dx then you'll need to do the whole mpfi swap and what not. a little more info on what you're looking to do would be real helpful.