IF you want a decently quick 6, 4cyl - spend the grand on a 88 or 89 with turbo and 5 speed.
But seriously.. the probe, 626, 6.. 4cyls seem to require ALOT to get anywhere. Our engines dont benefit much from headers so don't bother there, the stock manifolds are designed well enough.
But basic rule for most cars,
lightened flywheel, ($100 at a good shop)
good clutch, ($200-300)
good cold air intake ($50 pvc pipe from lowes + cone filter)
the 2.5 id pipe they have there, is perfect -
already has a 90 degree mandrel bend
requires only tapping a hole for the air
temp sensor. You'll need a coupler too,
cat back exhaust ($180 pacesetter from nopi)
jspec intake cam $130? from dorksport.
test pipe $35 from testpipes.com
about 760 so far, give or take.
A set of DZ lowering springs ($70 from ebay)
Front strut tower brace ($25 from ebay)
Realisticly.. this is the extent any 4cyl would go, minus
a n20 kit or turbo. You MAY see 15-17 whp from this,
and cut .4 or .5 off your 1/4 time, given you have a 5 speed.
If it's an auto.. you MAY see .2 or .3 off your time.
Corksport is about the only place that sells just the intake cam for the 4cyls. That item and the SS clutch lines are the only worthwhile items to purchase from them, UNLESS you enjoy paying TOP dollar (i.e. getting ripped off) for items.