There isn't much.   try http://www.3geez.com/

Swapping manual transmissions with an 84-87 prelude might give you better
gearing.  You could probably get better exhaust.... even the stock exhaust
manifold off of an 88-89 LXi is better.... but you'd probably have to plug
the extra o2 sensor port.  The 88-89 LXi has a different (better?) camshaft
to.  (some places list the 86-89 lxi as 110hp, some like the 88-89 as having
120).  If you get really wild, there is probably enough room to custom
install a turbo (there aren't any kits).

Most everything cool and really noticeable will be really expensive because
it will need to be custom.  You'd be better of with a 88+ civic or 90+
accord or 92+ prelude.  And if you really want cheap power you need
something that will hold a small block Chevy.... cause parts for those cars
and trucks are really cheap.

If you have an auto transmission, be carefull.   They can't handle too much
more power.
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Alex