After engaging in a pretty good amount of research on the eighth gen (sixth-generation Si) and its K20, a few things became very apparent. First off, a solid exhaust and header upgrade will net some power you can actually feel. The numbers, of course, are all over the chart due to the fact that no two motors, or dynos, are exactly the same, but there are no doubt gains to be made. The other thing that kept popping up over and over again is how much of an improvement Hondata’s FlashPro can make to the Si. Inherent quirks like rev hang, and the downright annoying stutter that rears its ugly head when the car is still warming up, can be eliminated completely with the plug-and-play module. Of course, the FlashPro’s biggest attribute is its ability to allow fine-tuning of the vehicle and wring out every bit of power from those new bolt-ons.
For the first round of initial testing, I contacted Vibrant Performance to try out its Cat-Back exhaust system and high-flow cat-equipped header. Doug MacMillan from Hondata was kind enough to ship me a FlashPro system, and as always, Elton Lo opened up the bay door to his dyno at Raceline so I could get some before and after numbers. The only modification to the car thus far is a Type One OEM-style intake. This kit uses a plastic snorkel that sits inside the front bumper and channels air through the factory ducting and into the airbox. Type One includes a high-flow panel filter and a carbon-fiber lid, along with an aluminum arm to replace the factory rubber version. This intake kit seems to be an improvement over the stock system, but is much better suited for an Si coupe or ’09+ sedan, as both chassis feature a foglight grille that can be cut out and direct air right to the snorkel. For the ’06–’08 sedan owners, the foglight openings are integrated into the main grille.
While I won’t bore you with every step of the install, since this is simple stuff that can be done in your garage with basic hand tools, I will point out some of the areas that might look a little strange to newer-generation Si owners. If you’ve only had experience with, say, D, B, and H-series motors or perhaps a K-swapped Civic or Integra that has far more room under the hood than the eighth gen, you might not like working on this chassis too much. I fit into the above category as I’ve owned, worked on, and swapped a number of D and B-series motors and worked on K-swapped cars, but I’ve never dug into the ’06+ models. The first thing I noticed when popping the hood is that the majority of the valve cover is hidden by the car’s windshield wiper cowl and accessing the exhaust manifold bolts on the head is a bit of a pain. Removing the plastic cowl and metal support tray is necessary to get your hands, and your ratchet, somewhere near the intended target. The other issue with the header removal has to do with the game of Tetris that you have to play with the top portion of the cast manifold from behind the motor. There’s not enough room to go out the top, so you’ll need to remove a bracket or two underneath the car in order to squeeze it through. Fortunately, an aftermarket header is much slimmer and will snake through fairly easily.
The Vibrant Performance header that I requested is armed with a high-flow cat and a heavy-duty flex-pipe to compensate for engine torque and movement. The design is light-years superior to the factory manifold, and appearance-wise, the welds, flanges, and build construction are top-notch. The necessary bungs required to plug in the factory oxygen sensors are there, and every bit of hardware needed for installation is included.
The Vibrant StreetPower Gen2 exhaust system is comprised of a CNC mandrel bent, 2.5-inch system with a straight-through muffler and a nice sized resonator to keep the noise levels tolerable. Installation couldn’t be any easier as the three-piece Vibrant system is a direct replacement for the factory exhaust system. The first thing most people want to know when talking about an exhaust system is “How loud is it?” I’ve yet to hear a whisper-quiet eighth gen, as just about every exhaust system on the market is comprised of 2.5 to 3-inch exhaust piping on an already hyperactive K20. Impossible to describe in words, I will say that at start-up the exhaust is certainly louder than stock, and if my neighbors didn’t have regular guitar jam sessions after 10 p.m., I would feel a little guilty for firing the car up in the morning for work. On the road, at cruising speeds, there’s a noticeable increase in “hum,” but it’s not overpowering. Under full throttle, the Vibrant Performance system is, of course, quite a bit louder than stock, but any Honda enthusiast (whether they’ll admit it or not) will crack a smile at the sound of this exhaust system as the VTEC crossover materializes. The deep, aggressive note barks when the throttle is blipped, rather than sounding raspy or cheap.
One of the main reasons I wasn’t expecting much from these upgrades is due to my experience with B-series motors where a few bolt-ons didn’t typically make a massive difference. The K series is a completely different animal. From a tuning standpoint, working with the ability to adjust the VTC will make a big difference in not only the motor’s power output, but also real-world drivability. Initially, Elton tried a preset map for an Si equipped with an intake, and the results were an extremely lean condition, specifically on the bottom end (below 5,000 rpm), further proving that not every motor is the same. These preset maps are more of a starting point than a replacement for actual tuning on a dyno.
On the road the difference is immediately noticeable. I headed out to the street with my set of trusty earplugs, which is something I always do when adding parts that will increase noise so that I can get a more realistic feel, rather than a placebo effect from increased cabin decibels. Bottom-end acceleration hadn’t changed much at all, and that’s a very good thing. The free-flowing exhaust and header would typically cause a loss on the bottom and an increase at the top end. With Elton tuning via the FlashPro, he was able to make up the difference by adjusting the VTC and other parameters, and there was virtually no loss. After 4,000 rpm is a different story, as the power increases steadily all the way to redline without any hiccup. The power can certainly be felt and gives you the impression that it’s just going to keep pulling right past that 8K redline. Passing power on the freeway saw a dramatic change as well; staying in sixth gear is just fine for overtaking slower drivers. The car managed to make 200 whp, and that’s with a cat. Elton is pretty confident the numbers would have been a bit higher with a freer-flowing intake, and we’ll find out in the near future.
The Vibrant Performance and Hondata FlashPro combo exceeded my expectations, and though I had my reservations, I’m now a believer. Next up in the engine department is a new set of drop-in cams, a better intake, and another trip to the dyno to let you know how they did. Stay tuned…