2007 Civic Si Sedan - Project Si: Initial Bolt-ons

After trying a few directions, the top portion of the OEM manifold simply wouldn’t squeeze through and we had to remove a few brackets.

After trying a few directions, the top portion of the OEM manifold simply wouldn’t squeeze

Exhale (Exhaust)
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.

Elton snakes the new Vibrant header and high-flow cat through without a problem, and here you see the exhaust/header/cat system together, just before the oxygen sensors were bolted in.

Elton snakes the new Vibrant header and high-flow cat through without a problem, and here

Tuning
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…

Line 1 (blue): After initial tuning with FlashPro and T1R intake, this served as our baseline—185 whp/ 134 lb-ft. Line 2 (red): Vibrant exhaust installed and Elton fine-tuning the FlashPro—192 whp/ 140 lb-ft. Line 3 (purple): Final numbers after cat-equipped Vibrant header was installed and final changes made to FlashPro—200 whp/ 145 lb-ft.

Line 1 (blue): After initial tuning with FlashPro and T1R intake, this served as our baseline—185 whp/ 134 lb-ft. Line 2 (red): Vibrant exhaust installed and Elton fine-tuning the FlashPro—192 whp/ 140 lb-ft. Line 3 (purple): Final numbers after cat-equipped Vibrant header was installed and final changes made to FlashPro—200 whp/ 145 lb-ft.