Besides the basics like a cold air intake and an exhaust, and any other factory equipment you swap or bolt on, know that you are not playing with a Honda Civic that has endless bolt on goodies. You want to look good or go faster, you're going to have to either put in the wrench time and work around many engineering challenges... or have the money to pay people too do it for you.
That said, you can make just about anything kick a Ferrari's ass... These cars are a WAY better baseline then any Honda.
- True dual exhaust (two pipes all the way to the back), or open up what you have half an inch wider proper consistent diameter tubing.
- Cold air intake will give it grunt, better acceleration and a few horses. Strapping a cone filter six inches from your exhaust manifold is NOT a cold air intake. Do it right, move your battery to the trunk, cut the battery box out and run the filter down in the bumper.
As far as factory equipment... Well there is LOTS of cool things you can add for looks and function if you know or see what you want and grab it at the junk yard. But there are a few performance tweaks...
- If you have no intentions of any independent fuel or ignition systems, a computer (PCM) from a 2002-2004 300M SPECIAL will give you a real nice edge. More aggressive tune, and the transmission shifts quicker and firmer.
- Change your transmission gears to the one found in any LH car that has a 2.7, or find a 300M Special. You can access the gears from the panel at the rear of the transmission once you remove the mount. Easy easy easy job. For the cost and work involved, this offers the BEST difference in power. If you got money to throw away, find a set out of a Prowler, or get a set of Prowler Pro Gears.
- Police/Special Sway bars, they offer a 35% gain in cornering performance, also the springs are stiffer.
Now for the real stuff...
- You can build a stroker out of your 3.5... Would require you to get a 4L crank, pistons, rods, bearings/rings. Appropriate machine work and you got a real nice torque difference.
- Turbo it... Which is my end goal.
- Inerita Performance offers a few goodies for our motors... From three stages of cams, to port and polished heads that optionally offer bigger valves.
- Bore out the throttle body (about $100).
- Intake Spacer kit was mentioned, something worth adding.
- Port and polish your lower intake manifold
- Can try a LX intake manifold swap
- High stall torque converter
- Limited slip differential
I'll go on, but your bank account is likely empty.