throtl Surprised a Subscriber With a Full 2015 Civic Si Build — Here’s the Whole Sheet
Video by throtl — “Surprising our SUBSCRIBER with HIS DREAM CAR BUILD! (Full Transformation) 2015 Honda Civic Si,” Dream Build 11. We’re covering the build; all footage and credit belong to throtl. This is informational commentary, not the seller of any part shown.
The best builds aren’t about one hero part — they’re about a plan. For the eleventh entry in their Dream Build series, the crew at throtl took a subscriber’s 2015 Honda Civic Si and rebuilt it end to end as a surprise. What makes the car worth breaking down isn’t any single upgrade; it’s how a stack of parts from a dozen different brands were chosen to pull in one direction — a cohesive, road-focused 9th-gen Si that handles, stops and looks the part without chasing a headline horsepower number. Here’s the full build, grouped by system, and what each choice teaches about doing a Honda build the right way.
Why the 9th-Gen Civic Si Is Such a Good Build Base
The 2015 Si sits at the end of the ninth-generation Civic run, powered by Honda’s 2.4-liter K24 four-cylinder backed by a slick six-speed manual and a helical limited-slip differential — from the factory. That combination is the whole point. It’s a naturally-aspirated, front-drive chassis that was engineered to be revved and rowed, so the fundamentals a builder actually wants — a good gearbox, a torquey-for-its-size engine, a genuine LSD — are already there. You’re not fixing a weak platform; you’re sharpening a good one. That’s exactly why throtl’s build spends its money on grip, control and stopping power rather than trying to reinvent the drivetrain.
What a Civic Si Build Can Become
Part of the appeal is how many directions the same starting point can go. Owners take the K24 Si down very different roads: some stay naturally aspirated and focus entirely on handling and looks, like this car; others add forced induction and turn a mild-mannered daily into a serious street weapon; others go deep on the interior and audio for a clean show build. The common thread across the ones that work is that the owner picks a clear goal first, then matches wheels, suspension, brakes and drivetrain to it — instead of bolting on unrelated parts and hoping they add up. throtl’s car sits firmly in the fast-road-and-show camp, and the parts list reads exactly the way a coherent build in that lane should. Our performance mods hub walks through how those pieces relate before you spend a dollar.
Wheels and Tires: Kansei on Falken
Nothing modernizes a Civic faster than the right wheels, and the Si got a set of Kansei wheels wrapped in Falken tires. It’s a smart, restrained fitment choice: Kansei has built a following for clean, motorsport-flavored designs at a sane price, and Falken is a go-to for enthusiasts who want real grip without stepping up to boutique track-tire money. On a light front-driver, wheel and tire choice is never just cosmetic — unsprung weight, wheel width and tire compound shape how the whole car turns in, puts power down and rides. Get the diameter, width and offset right for the car’s new ride height and you flatter the whole build; get them wrong and you fight rubbing and poor manners forever. Our wheels & tires hub and tire buying guide cover the trade-offs that decide whether a fitment works.
Handling: Blox Coilovers and Hybrid Racing
This is where the build gets serious about being a driver’s car. The suspension is built on Blox Racing coilovers, giving adjustable ride height and damping so the stance and the handling can be dialed in together rather than fighting each other — a slammed car on the wrong spring rate handles worse than a stock one, and coilovers are how you avoid that. throtl paired the coilovers with parts from Hybrid Racing, a brand Honda owners know for precision chassis and shifter hardware that tightens up how the car feels to drive. The lesson here is textbook: springs and dampers to control the body, quality supporting hardware to sharpen the inputs, and everything set up as a system so the ride height you chose for looks is also a ride height that works.
Brakes: EBC to Back Up the Corner Speed
More grip and more corner speed demand more stopping power, and the Si got an EBC Brakes upgrade to match. Better pads and rotors are the sensible next step once a car can carry real speed into a corner — they give you stronger, more consistent bite and better resistance to fade when you’re leaning on them on a good road. The key detail most people miss is that pad compound is a choice, not just a brand: a fast-street pad is a very different animal from a track pad, and matching the compound to how the car is actually driven is what makes the pedal feel right. Our brake refresh hub explains how pad compounds change the pedal and when an upgrade is worth it.
Drivetrain Feel: An Action Clutch
The Si’s six-speed is one of its best features, and throtl protected and sharpened it with an Action Clutch. An upgraded clutch does two jobs on a build like this: it adds holding capacity so the driveline can cope if the car ever sees more power down the line, and — depending on the disc chosen — it can give the pedal a more mechanical, positive engagement that suits a car built to be driven hard. It’s a quietly important upgrade, because the clutch is the link between the engine and everything the wheels and tires are now capable of. Do it while the car is apart for the rest of the build and you save yourself a second labor bill later.
Breathing and Cooling: Takeda Exhaust and a Koyo Radiator
Two changes here free up the K24 and keep it healthy. The car runs an AFE Power Takeda cat-back exhaust, which frees up a little flow and, more importantly on a naturally-aspirated Honda, gives the engine a voice — the classic reason this is one of the first mods on almost every Si. Backing it up is a Koyo radiator, an upgrade that matters more than it looks: a bigger, more efficient aluminum radiator gives you cooling headroom for spirited driving and hot days, which is cheap insurance on any engine you plan to actually use. Neither part is about big peak power; both are about making the car better to live with and drive. Keeping that engine healthy also comes down to the basics — staying on top of oil changes is the cheapest reliability insurance a K-series gets, and our oil change hub covers it.
Interior: Corbeau FXR Seats
Inside, the biggest change is a set of Corbeau FXR seats. A proper fixed-back or reclining sport seat is one of the highest-impact interior upgrades on a build like this — it holds you in place through the corners the new suspension and tires make possible, transforms how connected the car feels, and instantly modernizes a cabin. It’s also the kind of upgrade that photographs well and shows the car was built to be driven, not just parked. As always with aftermarket seats, the important detail is mounting them correctly on proper brackets and rails so the seating position and safety are right.
Carbon and Aero: Zen Carbon, Password JDM and Tecnocraft
The finishing layer is carbon fiber, sourced from Zen Carbon Fiber, Password JDM and Tecnocraft Composites. Carbon pieces do double duty on a build like this: they shave a little weight in the right places and set the visual tone, giving the Si that motorsport-adjacent look without a giant wing statement. The restraint is the point — a few well-chosen carbon pieces read as intentional and cohesive, where a random assortment reads as a parts catalog. Password JDM and Tecnocraft are long-standing names in the Honda carbon world, which matters, because fitment and finish quality on carbon parts vary wildly and a good piece is worth the extra money.
Audio: PRV Audio
The build also got a sound-system upgrade courtesy of PRV Audio. A car this thoroughly built deserves a front stage that isn’t stock, and audio is one of the areas where a considered upgrade — better speakers, proper amplification, sensible installation — pays off every single drive. The trap here is buying the biggest subwoofer instead of building a balanced system; the wins that actually improve daily listening usually come from the speakers, the amp and the install, not raw output. Our car audio hub covers how to upgrade a system in the right order.
The Unsung Part: WD-40
One name on the build sheet isn’t a performance part at all: WD-40, the sponsor. It’s worth a mention because a build like this lives and dies on the unglamorous stuff — freeing seized fasteners, protecting hardware, keeping a project moving instead of snapping bolts. Every big build is really a hundred small jobs, and the products that make those jobs go smoothly are the ones nobody films but everybody needs.
The Takeaway: A Cohesive Honda Build
What makes throtl’s Civic Si work isn’t any single part — it’s that the parts agree with each other. The Kansei wheels and Falken tires set the grip; the Blox coilovers and Hybrid Racing hardware deliver the handling that grip promises; the EBC brakes back up the corner speed; the Action Clutch protects the drivetrain; the Takeda exhaust and Koyo radiator make it breathe and stay cool; the Corbeau seats, carbon and PRV audio finish the car inside and out. That’s the real lesson for anyone eyeing their own 9th-gen Si — or any enthusiast Honda: pick a clear direction and build the whole car toward it, matching each system to the last, rather than bolting on unrelated parts and hoping they add up. The Si rewards that discipline as well as anything on the used market.
Planning something similar? Start with our performance mods, wheels & tires and brake hubs — and keep the maintenance dialed with the oil change guide.
