I have a 1990 prelude si and im rebuilding the engine so i need some advise. is the engine a good of bad engine when it comes to modifying? im not planning on turboing or adding nitrous, just headers and a good intake and possibly doin some stuff to the fuel system to feed it a little better. so if you know some stuff to help me out the info would be greatly appreciated but please dont screw me around. o yea i have heard the b21a1 is damn near impossible to bore because of the material the piston walls are made of is this true?

 

You're going to have a hard time finding aftermarket support for that engine. You may be able to find a header or intake for it, but probably not much more then that. Don't expect to notice a difference just from the few bolt-ons that you find, I have yet to see a manufacturer that makes any cams or pistons for that engine.

Just as long as you know that while it may be a B21, it actually has nothing in common with any other B16/17/18A,B,C or even the B20B/Z. So internals, and almost every part is not interchangeable.