With just an AEM intake and...
With just an AEM intake and a DC Sports header and exhaust, the Si was able to put down just over 194 hp. Hondata's reflash did little for top-end performance, but we got an additional 30 hp in the midrange and almost 27 lb-ft of torque from nothing more than plugging in the new ECU.
Hondata's reflash does three things, three very important things. First, it lowers the VTEC engagement point to a more useable 4,500 rpm-something we've seen pick up midrange power in the past on VTEC Hondas and is kind of a given when it comes to easy places to find lower-end Honda horsepower. With the Si's aggressive cam profile coming into action at 4,500 rpm, you can just watch the dyno curve take a turn for the better, almost straight up. How did Honda miss this? Just before 6,000 rpm, all this translates into our 30 extra horsepower we found. Sweet. Power gains are minimal at best from there on out and all tapers off just before 8,500 rpm-about the same as what we would have expected from the stock ECU with just a redline increase. But Hondata does something a little out of the ordinary when it comes to the VTEC switchover point: It's not really 4,500 rpm, at least not always. They created a window between 4,500 and 5,800 rpm in which VTEC may be activated. Below this threshold, it's always off. Above it, it's always on. But inside that 2,300rpm VTEC window, valve lift and timing are all determined based upon throttle. At part throttle, the camshafts make use of their milder side, while at wide-open throttle their maximum lift and duration are taken advantage of. Did Honda miss something here? Yes, but it was arguably intentional. The Si, like all K-series Honda engines, meets low emissions vehicle status requirements. So it's likely they weren't willing to push the envelope much further with this K engine in hopes of a bit more power at the expense of their coveted LEV-2 status. Who can blame 'em? Besides, this wouldn't be the first car we've seen detuned straight from the factory.
VTC is controlled electronically...
VTC is controlled electronically via the ECU and this 50-degree adjustable gear mated to the end of the intake camshaft. Hondata's reflash tailors intake camshaft phasing and is partially responsible for the 30 hp jump we saw.
Second, when it comes to duration, Hondata addresses this here as well by means of advancing the intake camshaft angle. The K20Z3, like other K-series engines, employs two different forms of technology when it comes to the intake camshaft: Honda's tried-and-true VTEC combined with VTC (Variable Timing Control). VTC continually adjusts intake camshaft phasing electronically while VTEC continues to do what it's known best for-alter camshaft lift, duration and timing via its third lobe system on both camshafts. The good news for i-VTEC (VTC and VTEC) owners is that the VTC part can be altered within the ECU, which is exactly what Hondata did. In stock form i-VTEC allows for a maximum of 50 degrees of timing adjustment to be made. To get the best results power-wise, we really only need about 20 to 25 degrees of adjustment throughout the rpm range, but Honda implemented additional leeway for emissions reasons. While we like i-VTEC for the performance benefits it gives us, it's really responsible for why the Si burns so damn clean. Speaking of emissions, the good news is that Hondata's reflash makes little difference, so California readers can rest easy.
The Hondata reflash also raises...
The Hondata reflash also raises the rev limit from 8,000 to 8,600 rpm.
Third, Hondata also raises the rev limit from 8,000 to 8,600 rpm. Right now this change makes little difference since our power difference at the top end is negligible. We suspect swapping in a set of '06 TSX cams may prove different though. The added lift and duration that both the intake and exhaust cams possess should increase our potential for top-end power a bit. For now, our power gains remain in the 4,500 to 6,000rpm zone, which is after all a reasonable place to spend a lot of time at, especially since this is a daily driver. We should also note that our test Si was already outfitted with an AEM cold air intake, a DC Sports race header and a DC Sports exhaust system. Without these breathing upgrades, our 30hp gain realized from the reflash would likely be less-much less. Since the reflash finds much of its power from the advanced intake cam timing, a free-flowing intake and exhaust is pretty important.