it really depends on what chassis it is going in. Also, if you plan on keeping P/S or A/C, then chances are that you will want to go with a B series. If you are building an all out race car, go with a H22A or a F20B. I personally prefer the F20B, since is it 99% similar to the H22A (same head as jdm H22A type S, but has a shorter stroke and slightly smaller pistons.) I would get a F20B, get it sleeved, and run a set of 11.5:1 pistons in 87mm instead of the 85mm that it comes with. You will have an engine with a stroke that is almost as short as a B18C5, but with much larger pistons. It will be about 2050cc's (2.1L) and should be able to pull 9k rpm just as easily as a B18C5. It has 200hp stock, and an 8k rpm redline (fuel cut at 8300rpm like a B18C1). They are cheap and a lot of parts are interchangeable with the H22A. It has steel sleeves, not that FRM **** that the H22A has. I have built a few H22A's, and the FRM sleeves are a hastle when you want to run oversized pistons. FRM sleeves cant be bored or honed.