PRODUCT DETAILS
HKS Hi-Power Cat-Back Exhaust - 2017-2021 Honda Civic Si
Honda gave the 10th gen Si a genuinely good turbo engine and then wrapped it in one of the quietest exhausts they've ever fitted. That's the problem this solves. The HKS Hi-Power replaces the whole system from the cat back with a race-derived layout and dual titanium tips, and it turns a car that sounds like a rental into one that sounds like what it is.
Sedan Or Coupe? Different Systems
Check your body style before ordering, because these aren't interchangeable.
31006-BH002 fits the Civic Si sedan.
31006-BH001 fits the Civic Si coupe.
The rear sections route differently between the two cars, so match yours rather than assuming any Si system fits.
81dB To 92dB, So Know What You're Buying
Being direct about this, because it's the biggest change you'll notice.
HKS measures the stock Si at 81dB and this system at 92dB. That's a substantial increase, and decibels are logarithmic, so the difference is bigger than the numbers suggest. This is not a subtle exhaust.
If you've been frustrated by how muted the factory Si sounds, that's exactly the point and you'll love it. If you park in a shared garage, leave for work at 5am, or have neighbors you like, factor that in honestly before you order.
The tone itself is the Hi-Power note, which is deeper and cleaner than the raspy drone cheaper systems produce on a small turbo engine. You're getting volume with quality behind it rather than just noise.
Titanium Tips, And Not Just For Looks
The dual 97mm titanium tips are the visual signature of this system, and titanium is a genuine functional choice rather than a styling one.
Titanium handles extreme heat far better than stainless, so the tips hold up to sustained exhaust temperature without discoloring badly or degrading. On a turbo engine, where exhaust gas temps run higher than a naturally aspirated car, that matters. And the way titanium takes on color with heat is why these look better after a year than they do out of the box.
Sized For The 1.5T
The center pipe runs 60mm, stepping down to 50mm in sections, feeding the 97mm tips.
That sizing is deliberate. Oversize the piping on a small turbo engine and you lose exhaust velocity, which hurts spool and low-end response. The 1.5T is a small displacement engine relying on its turbo, and keeping velocity up matters more here than chasing the biggest possible pipe. HKS sized this to flow considerably better than stock while keeping the car responsive where you drive it.
Ground Clearance Was Considered
Worth knowing if your Si is lowered or heading that way. The system maintains 115mm of road clearance, which means it isn't hanging down waiting to catch every driveway and speed bump.
That's a real design consideration on a car a lot of people drop, and it's the difference between an exhaust you enjoy and one you're constantly wincing about.
SUS304 Stainless
Built from SUS304 stainless steel, which resists corrosion far better than mild steel and holds its finish. On a car that sees winter roads and salt, that's what determines whether the system still looks right in five years or has gone rusty and tired.
Fitment
2017-2021 Honda Civic Si Sedan (31006-BH002)
2017-2021 Honda Civic Si Coupe (31006-BH001)
Select your body style at checkout.
Who Should Run This Exhaust
This is for the Si owner who's spent time wishing the car sounded like it drives. You get real volume, a proper Hi-Power tone, titanium tips that look better as they age, and stainless construction that outlasts the car. Just be honest with yourself about the 92dB before you commit. Match your body style, bolt it on, and go enjoy the noise.
Fits: 2017-2021 Honda Civic Si, sedan (31006-BH002) and coupe (31006-BH001). Type: cat-back exhaust system. Muffler: Hi-Power with dual titanium tips. Tips: 97mm. Center pipe: 60mm, stepping to 50mm in sections. Material: SUS304 stainless steel. Sound level: 92dB (stock 81dB). Ground clearance: 115mm.
2017-2020 Honda Civic Si