Getting 400 Horsepower From a Turbocharged K24 Swapped Subaru BRZ

After owning three Subaru BRZs in various states of tune, NASA Gulf South Time Trial competitor Kameron Newman was confident enough to try a complete powertrain swap with some yet-to-be-tested items in his chassis of choice. Working as a product design engineer at Geaux Moto, a Louisiana-based performance shop specializing in motor swaps, Newman was eager to introduce a proven, high-revving powerplant to his beloved BRZ chassis and stick a modern BMW gearbox between them.

With a wrecked 2018 BRZ TS from Copart and a long list of parts picked during late-night spending sprees, he was underway. The TS – a rare edition with only 500 sold – only cost him $9,000. “It had been wrecked twice, actually,” he began. “But I didn’t know that until I bought it. The damage was limited to the body, and the powertrain was in working order.”

Factory Fit

The car came mildly modified and the FA20 was fully functional, so there wasn’t much work required to make the car a functional cone carver, actually. “The TS edition comes with the bigger Brembos and a small winglet, which actually does something at speed,” Newman said. “Out of the box, it was faster on the autocross than my WRX ever was, even with half the power.”

He turned to Racecomp Engineering for a set of tailored shocks with Verus Engineering top hats, then added all of the BRZ SPL catalog, including front and rear control arms, front and rear toe arms, rear traction arms, and spherical bearings. To top it all off, he added an Improved Racing oil cooler.

The factory rotors were fortified with Girodisc two-pieces and clamped with Ferodo 2500 pads. A set of Apex VS5-RS wheels wrapped in 255-section Bridgestone Potenza RE-71RS tires rounded out the changes to the footwork.

It was quick enough, actually, to take Newman to the top of the time sheets in TT5 his first weekend out. Reasonably large fields in the NASA Gulf South region were the place he was able to enjoy a kind of camaraderie that he’d gotten accustomed to in autocross. “NASA continued the camaraderie — everyone in NASA TT is helpful — even if they’re in your class,” he said.

The pits were a warm place to be, but the straightaways seemed painfully long — long enough to have a cup of coffee before the next corner, sometimes. All while he was enjoying the playfulness of the chassis, he pined for the thrust of his 400-horsepower WRX. If that kind of power could be made usable in an FR layout, he might strike gold.

Though the FA20 ran and drove, Newman saw forced induction in his future, and felt the right way to blend boost and the BRZ chassis was by implanting a Honda K24.

Big Plans, Small Support

To better harness a medium-sized turbocharger matched to a modestly sized motor, Newman realized that transient lag needed to be minimized, and the best way to do that, by his way of thinking, was to fit a modern dual-clutch transmission.

“I bought the car with the plan of putting a K-series in it. That’s nothing new, but attaching the motor to a dual-clutch transmission is basically unheard of in a BRZ,” he began.

He considered several simpler solutions initially. There was thought of a Nissan/Infiniti CD009 transmission, but they’re known to have shift fork and synchro issues with long term track use. There was also the T56, but it isn’t suited to low-torque engines that rev high. The now-widespread ZF8HP automatic, easily integrated into all sorts of layouts with extensive aftermarket support, was briefly considered, but “it hasn’t been proven to work reliably at 8,000+ rpm in track conditions.”

BMW’s first-gen of DCT, the GS7D36SG, designed to handle a smooth-revving sixes and moderate displacement eights would be a far better solution. When paired to an S65 BMW engine, it can handle 8,400 rpm reliably, and the ratios are quite short with seventh being a 1:1. The price is a factor as well, with most coming in around the $2,000-mark.

At the end of a successful first year of competition with the car, Newman could point to a small collection of trophies on his mantle and a new motor sitting on a pallet in his garage. The stock K24A2 swap began late in October 2024 with the firm deadline of mid-March: the date of the first local NASA Gulf South event of the year. The K-Power Builder Kit provided the essentials for installing the lump in its new home. The kit came with an intake manifold, a rear water neck, an oil pan, and motor mounts.

The only required changes were the upgraded K20 oil pump that could withstand the higher revs, as well as a Honda 50° VCT gear, which allows the intake cam gear to have 50 degrees range of motion opposed to the factory 25 degrees, which increases midrange power.

“Before dropping the subframe of the BRZ to put in the Honda engine, I fully assembled the motor and transmission out of the car. I cleaned and painted the block and then set up the motor, which included the oil pan, intake manifold, turbo manifold, turbo oil/water lines, harmonic balancer, and all other accessories. Last added was the Clutchmaster flywheel and adapter to mate the Honda and DCT together,” he said.

Since the BRZ came with a boxer motor from the factory, the engine bay was wide enough to allow the K-series to go in from the bottom with everything fully assembled, even with the intake, turbo and turbo manifold attached. However, the factory BRZ transmission mount needed to be cut out and the transmission tunnel needed to be ‘massaged’ to accommodate the much larger transmission.

“I was able to locate the transmission where I wanted it with the correct driveshaft angle relative to the differential. After this, I 3D-scanned and designed the transmission mount in Solidworks, and manufactured it out of 3/16” steel sheet metal.”

When installing the drivetrain, Newman sent his OS Giken differential back to the manufacturer for a special unit suited to a DCT and high power. East Coast Drivelines set up the ring and pinion, and Speedtek Auto Racing made the 3.3 final drive.

Snail Trail

“I decided on a Garrett G30-770 with a 0.83 A/R. With testing on another racecar with a similar setup, we found this turbo allowed for a 1:1 backpressure ratio at the boost level I want to run. A 1:1 backpressure ratio means the turbo system is well-matched, the engine breathes efficiently, makes more reliable power, and runs cooler, all of which are essential for road racing, where consistency and reliability matter as much as peak horsepower.”

After choosing the right turbo, he made oil lines for it and custom fabricated a 3-inch oval downpipe to work within the spatial constraints around the transmission. Then in went two Improved Racing auxiliary coolers, a KoyoRad radiator, a custom Geaux Moto intercooler with a PWR core, a Radium drop-in hanger with fuel filter and regulator, as well as a Walbro 525 pump.

Systems Integration

Breaking new ground with a DCT-swapped BRZ required experienced powertrain specialists CANformance Engineering and their Kenneth Blomstedt jump onboard to assist Newman. Specifically, Blomstedt was integral in getting the Haltech R3 ECU to communicate with the BMW transmission.

“Currently, there aren’t too many options available for people who want this conversion. Most aftermarket ECUs require a gearbox controller to interpret the signals sent by the gearbox’s TCM,” Blomstedt said.

The medium of choice is the CANTCU system: a CAN-based transmission controller built specifically for BMW’s ZF8HP and DCT gearboxes.

The earlier DCTs, like the one in Newman’s car, “have a difficult logic on the shifting part, which requires different types of requests from the ECU, and it’s more complicated than a ZF8HP. When you add the fact that there’s no converter to smooth the shifts, it gets complicated,” said Blomstedt.

“The CANTCU steps in to translate. Since the transmission has its own brain – a TCM, which we can use to our benefit instead of getting rid of it – CANTCU basically translates the signals from the transmission into something the ECU can understand. In this case, it converts the requests into CAN signals that the ECU knows. Then the ECU can supply the torque requests and whatever else is needed.”

To do this, there are a few items Newman had to cover. First, the wheel speeds need to be dialed in so that the transmission can shift normally. “Unlike a ZF8HP, which has sensors on input and output shafts, the DCT has nothing on the output side, so it relies entirely on speed signals you’re sending it, and if they’re not matching up, it will not behave well. Shifting won’t be accurate. You must install additional sensors for this reason,” Blomstedt explained.

CANTCU has full documentation on every popular modern powertrain combination available for people like Newman and all installation notes for the supported ECUs. “Their documentation is thorough and I was able to get just about everything working using that. I had a few questions regarding wiring, and then they had to step in to help reflash the DCT TCM,” Newman said.

In Newman’s case, using the earliest version of the DCT came with its own hangups. It is more complicated in operation than those found in the later F-series cars. “Blomstedt had to remote into my laptop to flash in the E92 GTS software to remove the transmission’s immobilizer and adjust the differential ratio. This can be done directly through CANTCU with the later F-series 8HP/DCT transmissions.”

Another perk of running the CANTCU system is that it retains the OEM transmission control module within the transmission, retains OEM driveability in all situations, all safety functions, and does not require any soldering.

“The next hurdle was wiring the transmission, CANTCU, OEM E92 M3 shifter, and Seems Legit Garage paddle shifters all together. After many research hours and planning, I created a wiring harness that seemingly integrates all of these together. The CANTCU, shifter, and transmission are all being powered by one of the high amp outputs off the Haltech, the paddles’ wiring is running through the OEM clockspring, and everything is communicating together via CANbus networks, so whatever the Haltech sees, the CANTCU sees, and vice versa,” Newman said.

The powertrain started up on the first try — a long and satisfying return on hundreds of hours spent in his garage that winter. The next step was testing to make sure the transmission worked.After raising the car on the lift and running through all seven gears at low loads, the first gremlin reared its head. The absence of boost was quickly attributed to the engine harness ground on the valve cover. “This is a commonly known thing to avoid doing, but I was new to the Honda world. It caused bad ‘breaking up’ and misfires while in boost,” he explained.

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Once that was sorted, Newman could finally exhale and smile and a long-overdue smile. Running through the gears via paddles at full chat was “the sickest thing I’ve ever done,” he exclaimed.

Tried and True

The street testing done without any further issues, he commenced his first shakedown at NOLA, where he found another couple of flaws in the setup. Cracks forming on his turbo manifold forced him to abort, return to the shop, then rectify the issue with lots of filler and extra bracing. This rush made it possible to attend the next event, where he joined TT3 and set his own personal best, despite running TT4 power levels.

One item regarding the transmission needed to be addressed: a fourth-gear lockout. “Once on track, when revving the motor out in third gear and pulling the paddle for fourth, the engine would rev freely as if it were in neutral, then select fifth. Going up or down, I couldn’t find fourth,” he explained.

After sending Blomstedt his logs, Blomstedt recommended some Haltech shift settings and filling an additional quart of transmission fluid to prevent oil starvation. “It was due to some fluid starvation and too low of a torque factor that was causing this issue at first,” Newman added. Once that was solved, the car ran faultlessly.

Newman’s previous best lap at NOLA Motorsports Park in TT5 trim was 1:59. After the swap, the first weekend in an unbroken state yielded a 1:53 with plenty more on the table. In TT3 trim, Newman should have another 30 average horsepower.

At just 7 pounds, which is wastegate pressure, the K24 made 300 horsepower at the wheels. Newman has since increased boost and horsepower to 400. This is accessible not only because of the gearing, but because the powerband begins at 3,700 and builds to 8,000. “The motor never falls out of boost, and there’s another 100 pound-feet across the board,” he said proudly. The added power doesn’t come with much of a weight handicap, either. The whole setup only adds a hundred pounds to the total weight.

The ease with which he could string out long acceleration zones was wonderful, but slowing the car wasn’t quite so seamless. “If your foot is on the throttle, you cannot expect a seamless downshift. It usually executes a stacked downshift seamlessly, but that one time out of a hundred, it will struggle. At least there’s not much low end torque to lock the driven wheels.”

Despite the bump in power, the chassis coped well. “All I did was adjust the compression and rebound at both ends to reduce some oversteer,” he said.

Traction management has been made easier by having the ability to pull a paddle and short-shift to manage the torque. In slow hairpins, a premature upshift helps put power down. Still, mid-corner shifts, especially in the wet, can upset the car.

If You Build It

The manifold continues to be a thorn in his side, and while he’s band-aided the current manifold, something quality is needed if he’s going to turn up the boost. Once he’s able to build a turbo manifold of his own, he plans for 450 horsepower.

To handle this, he’s forecasted homebuilt aero and more rubber: a square set of 285-30/17 Vitour P1 he believes should fit under the factory bodywork with enough persuasion and fender rolling. Then it’s a matter of refinement.

“I want to make it the ultimate poor man’s GT3RS. I want to be able to send someone out for a few laps and have them come back raving. ‘Build me one now,’ they’ll say.”

To follow Newman’s progress, view is Instagram and YouTube pages which both share the same handle: @kamtechengineering