A real problem with the '90 Prelude is the fact that in the past, if you wanted to add a short ram, or even a cold air intake, you would have to move the battery in order to have enough space. Basically, you had to make a '92+ intake fit under the hood, which could be done with some minor modifications. I've done it on a '90 with some ease, just wasn't a direct bolt on.
I'm pretty sure they make a short ram intake for it now, although i'm not sure what happens to the battery, or anything else thats under the hood.
The stock air intake tubing can be a pain to get out too, as it goes down behind the engine, before coming back out, if I remember correctly. Very restrictive, and the engine would benefit alot from an aftermarket piece.