With a full factory-warranty for the duration of the vehicle's warranty (as long as you order the FP kit during the original sales transaction of the vehicle), superb fit and finish, and a very minor penalty in ride quality, the Factory Performance (now A-Spec for Acura) offerings have all proven to be great values, and the '04 Civic Si's setup is no exception.

The kit for the Civic Si is very similar to the A-Spec kit used on the '04 RSX, and even uses the same wheels and tires. Suspension tuning is also very similar and the ride characteristics are very close, though the Civic's suspension seems slightly more compliant. We tested a preproduction RSX A-Spec last year (at that time it was still known as Factory Performance) and I was astonished by the RSX's transformation.

The FP's influence on the Civic may not be quite as dramatic as the RSX's, and I'm not exactly sure why that may be, but the Civic does carry a bit more weight, and perhaps more importantly, a seemingly higher center of gravity than the RSX FP prototype did.

With approximately 25mm in ride height reduction, and stiffer spring rates, body roll is virtually eliminated, and transitional responses are excellent. While the RSX FP Prototype was amazingly neutral with even some useful oversteer available for the taking, there seems to be a bit more understeer dialed in to the Civic. When it comes to holding a line through a turn, the RSX FP Prototype stayed a bit more faithful than the Civic Si FP, which tended to understeer a bit earlier than I would have hoped. It's possible that the tires on the Civic Si FP we tested weren't fully scrubbed in (it was delivered to us with just under 1800 miles on the odometer, vs nearly 6000 on the RSX), but the Si's Yokohama AVS ES100s didn't seem to be quite as adhesive as they were on the RSX. Apart from a stiffer ride, another consequence of the reduced ride height is a reduction in suspension travel. In some extreme cases, the front suspension actually topped out (reaching full extension) over large heaves in the road.

One area that is an improvement (compared to the RSX FP prototype) is the steering. While the RSX's steering felt slower, number, and heavier than stock, the Civic Si suffers no such fate. In fact, the Civic Si FP's steering seems pleasingly quicker than the last stock Civic Si we drove (an '03 model).

The added grip of the wider 17" rubber pays huge dividends in terms of putting down power from the 160hp i-VTEC motor. While the '02-'03 Civic Si's would easily smoke either of its 15" front tires in the lower gears, wheelspin is largely a thing of the past on the Civic Si FP, except in extremely tight corners. This results in an improvement in 0-60 acceleration of approximately 0.2 seconds. In our testing, the FP averaged a 0-60 of about 7.5 seconds.

The additional grip from the larger tires offers a small benefit in terms of braking, but the stock pads are still prone to fading and shuddering during enthusiastic stints of mountain driving. The brake system would likely benefit from revised biasing as well - the front brakes tended to lock up (engaging ABS) well before the rear brakes, resulting in longer than necessary stopping distances. Careful modulation of the brake pedal improves things somewhat, but the car still needs more braking power.

The FP does nothing for the Civic Si's short gearing and a low rev ceiling (it's at least 500rpms conservative), so we still found ourselves banging into the limiter during spirited driving. A quick flash of the ECU from Hondata would help mitigate this issue.