Of course the best place to experience the Si is from behind the wheel. From that position you can fully appreciate the Si's seats, which are every bit as good as last year's seats, complete with the faux suede upholstery. (Unfortunately, taller folks may not be able to take their Si to the track in comfort - my helmet was planted into the headliner and I'm only 5'10"). You can also immerse yourself in the aural nirvana of that K20Z3. Even while idling, you may find yourself blipping the throttle a couple or four times just to hear the raspy burble of the exhaust. Now, start pulling out of pit lane and accelerate onto the track. You have a very nice exhaust burble in the lower rpm ranges, and then as you sweep through the midrange the exhaust note gives way to a pitch perfect howl from the intake as the VTEC mechanism switches over to the long duration, high-lift lobes. Engineers worked painstakingly on emphasizing the pleasing notes and filtering the other parts of the spectrum that bend your eardrums the wrong way, and in fact it's tuned to deliver a very muted sound at 3000-5000 rpms, normal cruising ranges. It's not all about the sound, though - what you're hearing translates directly into forward motion, and the engine revs so willingly it feels as if there's no flywheel mass, particularly when it crosses over into the full VTEC range from about 5800 rpms to the limiter (approximately 8300 rpm on the tach). (HONDA DEALERS, TAKE NOTE: This part of the Si driving experience should hook EVERY buyer, EVERY time. So, pluck an Si out of your first allocation and set it aside as a demonstrator model. Make sure it's fully and properly broken in, and then allow prospective buyers to tach it up as much as they want on their test drives. I promise, most of them will be hopelessly addicted and climb out of the demo cars fumbling for their checkbook. )
If you're familiar with the RSX Type S, you will be amazed by how the balancer shaft in the Si's K20Z3 completely eliminates the boominess of the engine sound and you will also notice how smoothly the K20Z3 operates throughout the revs. Additionally, the 6-speed shifter will feel amazingly familiar, too - in fact, the Si's gearbox feels almost exactly the same as the RSX Type S's, which is a pretty good thing. Ideally it would match the excellence of the TSX's gearbox, but it's not quite there. The only quirk I noticed with the car I drove on track was that finding neutral seemed a little more ambiguous than it should be. When rolling to a stop I had to double and sometimes triple check myself to make sure I hadn't pushed or pulled it too far and mistakenly selected a gear instead of neutral (update: This appears to have been something related to the heat generated from the hotlapping these cars were subjected to). As far as position goes, the shifter is mounted nice and close to the steering wheel and the throws feel about the same as the RSX-S' gearbox. Apart from the vague neutral position, I never had a problem finding a gear on track. Inside the gearbox, the first 5 ratios in the '06 Si gearbox are the same as the ones in the current RSX Type S, but 6th gear is about 12% taller to cut freeway revs noticeably. Now at 75mph it only cranks about 3300 rpms, which is about 500 rpms lower than last year's Si. The ratios are very well matched to the characteristics of the motor, and each redline upshift initiates another satisfying lunge to the limiter. The only downside is that these tightly spaced ratios now require an upshift to 3rd gear to reach 60mph, which will impact magazine 0-60 test times to some extent.
The K20Z3 marks the first fitment of a drive by wire throttle system to a K20 motor in the US. This was anticipated, but we were really hoping it wouldn't happen. So far, I've only met one drive by wire throttle system that didn't totally frustrate me, and that's the one found in the Acura NSX. The NSX's drive by wire throttle exhibits absolutely no lag or delay to the demands of your right foot and operates in an absolutely transparent fashion - and that's the way it ought to be. Unfortunately, this has not been the case in the TL, Accord and TSXs we've driven with drive by wire. The biggest problem I've had with the DBW system on these cars is that the lag throws the timing off when you're trying to upshift or downshift in a hurry. Unfortunately, the Si's DBW system still exhibits this annoying lag, but in the Si's case it doesn't impact the shifting quality. Unlike the Accord, TL, and TSX, the Si actually holds revs noticeably in between shifts, effectively smoothing the upshifts and avoiding the problems that are most noticeable when shifting the TSX very quickly. In other situations, the impact of the lag isn't that bad, so throttle response feels pretty good on the track. So in the end, the Si's drive by wire throttle is an improvement over previous 4 and 6-cylinder systems from Honda, but there's room for further improvement.
The chassis of the 2006 Si has received significant enhancements, starting with the redesigned front and rear suspensions which are bolted to a strengthened body and connected to the road by way of super high performance Pilot Exalto PE2 tires and (finally!) a Limited Slip Differential. Compared to the 2006 EX Coupe (which is already stiffer than the Sedan), the Si's suspension uses 17% stiffer spring rates all around, 45% stiffer damper rates up front and 40% stiffer damper rates in the rear. In terms of roll stiffness, the Si runs a solid 28mm bar up front (104% stiffer than EX) and a 17.0mm rear bar (465%(!) stiffer). The added roll stiffness is appreciated, as the Michelin PE2s generate quite a bit of lateral and longitudinal grip, and the LSD allows you to start putting down more power sooner, leading to higher cornering speeds. Speaking of the LSD, it performs brilliantly in the Si. Most of the time it's invisible, in that it doesn't influence the steering feel at all, but when it comes time to put the power down, it really pays off. I only drove the car briefly on the street, but I never caught even a whiff of torque steer on the street or the track.
EPS (Electric Power Steering) made its first appearance on an Si in 2002, and it returns with the '06 Si. At 13.6:1, the steering ratio is rather quick, even quicker than the S2000 (14.9:1), and not surprisingly, the Si responds to steering inputs very quickly. On track, it never felt twitchy or unstable, and feedback through the steering wheel is improved compared to the previous generation Si. The system is designed to vary steering effort with speed, but it was not noticeable to me on the track. The steering wheel is a proper 3-spoke design, with a relatively fat leather-wrapped rim. You can adjust both the reach and the tilt angle of the steering wheel to suit your preference.
The Si's brakes have also been beefed up a bit this year. Up front the car runs 11.8" vented rotors (up from 10.3"), clamped by dual piston calipers. The rear brakes remain at 10.2", but the '05 Si's 7"+8" tandem booster has been replaced by a single stage 9" booster. Honda claims significant improvements in performance in one of their standard fade tests (15 consecutive 60-0MPH stops with the vehicle at GVWR). This particular track layout wasn't too demanding of the brakes, but there were a few areas where you could get into the binders pretty hard, and the Si's brakes felt very good in those situations. While we recognized the telltale scent of heavily worked brake pads, we never sensed any fading or change in pedal effort. What we did notice was that under heavy braking, the Si exhibits some nosedive and the rear end lightens up a little more than we like. But then again, this Si goes, stops and sticks like no other Si before it, so the suspension is dealing with much greater negative G's than any previous Si suspension has been asked to deal with.
On track, the dual tiered design of the instrument panel may not be the ideal setup. The speedometer is easy to spot, but when trying to keep track of the revs, my eye instinctively scanned the upper tier for the tachometer. When I wanted to check the revs, I had to remember to glance further down to the lower tier to find the tach. At speeds approaching triple digits, you can see why this may be less than ideal. Fortunately, it's really easy to shift the Si by sound, but until you get comfortable with that, there's a shift light positioned in the upper tier just to the right of the speedometer to help you along. It begins flashing at 7400 rpms and keeps blinking until you hit the redline, at which point it turns solid red.