FYI: I replaced my D15b8 with a D15b7. I got a more than a 34hp bump out of it. In fact, it dynoed 90.6hp/90.9tq... It may have made the ride a little TAD bit more fun, and it's amusing at best... but the unfortunate part of it is that it won't make any of it until 4000rpms. A DOHC motor won't give you those problems.

If you boost a D series, just don't go buying a gigantic turbo that you can't spool... a little boost goes a long way with Honda engines because they have higher compression than most factory-turbocharged engines. You won't need a lot of boost to make respectable power. Spend nothing on mods until you want to boost it unless money is no object. Everything on your intake and exhaust will have to be replaced when that happens.