After the UK recommissioning delivered a track-day-legal 911, the question was never if it would race, only when. The car had a racing pedigree stretching back to Chicago in 2006 and a supercharger that had always been part of its identity. What it needed was a team capable of transforming an ageing, American-spec track car into a fully homologated British race car. That search led to three specialists who would collectively spend years reshaping the 903 from the ground up.
Phil Brough of Brough Motorsport became the project's lead race engineer, responsible for the car's overall mechanical health, safety preparation and trackside operation. Russel Lewis of RSR Engineering, a former Porsche Technician of the Year, took ownership of the engine and gearbox. Dave Rowe of Electronic Performance Systems brought decades of MoTeC expertise to the engine management and electronics package. Together, they gave the project its competitive credibility.
Race Homologation: Making it Legal
Before any serious development could begin, the car had to meet the safety requirements for competitive circuit racing under Motorsport UK regulations. This phase involved a substantial amount of work: not glamorous, but essential.
The most fundamental requirement of all was a valid race licence. Kenn van Hauen earned his Motorsport UK National B race licence at the ARDS driver training and assessment course at Castle Combe Racing School on 24th February 2022, a rigorous test of both car control and circuit knowledge that is a prerequisite for all Motorsport UK-licensed competition.
A ten-point bolt-in roll cage by Safety Devices was installed, FIA homologated and MSA recognised, and purpose-built for a left-hand-drive F-model Porsche 911 Coupe without a sunroof. Door bars, transverse bracing and reinforcement plates were fitted throughout. Alongside this, a Lifeline Fire Marshal Zero 360 suppression system was installed: a 2.25kg Novec 1230 gas unit with three nozzles in the engine bay and two in the cabin, dual pull cables, and full FIA and MSA approval.
The driver environment was equally transformed. A Recaro Profi SPG XL race seat replaced the worn-out, out-of-date and out-of-regs bucket seat, fixed in position for optimal support and stability. Schroth Profi 3x2 six-point harnesses were fitted, HANS compatible and FIA homologated to 8853-2016. The windscreen was upgraded to a tinted, heated, dual-circuit laminated unit by Ricky Evans Motorsport, fully E-Marked and road legal globally. Lexan polycarbonate windows with integrated slider vents completed the interior safety package. A VBOX Video HD2 dual-camera on-board video system was also required by regulation, with one camera covering the road ahead and one covering the driver, ensuring that the cause of any race incident can be established from recorded evidence. The system overlays MoTeC data in real time on HD footage with pit-to-car radio audio included, making it a comprehensive training and review tool alongside its regulatory function.
The Gearbox: RSR Engineering Rebuilds the 915
In January 2022, Russel Lewis at RSR Engineering carried out a full inspection, reconditioning and upgrade of the 915 gearbox, at no expense spared. The transmission was stripped to bare components, measured, cleaned and rebuilt with a comprehensive list of new and uprated parts: asymmetric first gear dog teeth, new synchro bands throughout, an uprated first-to-second spider and sliding sleeve, and a modified fifth gear to eliminate sticking under race loads.
One of the most significant improvements was the installation of a milled stainless steel figure-eight plate, replacing the weaker two-piece cast original. This precision component better supports both main and pinion shaft bearings and incorporates an oil groove to promote lubrication to the input shaft bearings. All castings were vapour blasted and chromated on reassembly.
Shift quality was transformed at the same time by the WEVO short-shift solution: a spring-centred WEVO Shifter with reverse lock, paired with a WEVO Precision Shift Joint that eliminates the troublesome friction pinch clamp on the rear of the shift tube, replacing it with a three-bolt flange assembly for a permanently secure connection.
Engine Seizure and Full Rebuild
On 18th March 2022, during a pre-season track day at Donington Park, the engine seized. Investigation revealed that a faulty oil inlet check valve had caused oil starvation, resulting in two seized connecting rods and debris distributed throughout the engine. A car that had survived decades of American club racing had been stopped in its tracks by a single failed component. It was a significant setback financially, emotionally and in terms of lost development time. The engine was sent to Russel Lewis at RSR Engineering for a full forensic strip and rebuild, work that would not be completed until February 2023.
The Porsche Carrera 3.2 (a 3,166cc Type 930/21 unit from 1985) was rebuilt from scratch. The crankshaft was removed for specialist repair and retreatment. The crankcase was machined for shuffle pins and barrel seats, and all oil galleries cleared of debris. Every cylinder head stud was replaced with an ARP uprated kit. All main bearings, big-end bearings and little-end bushes were renewed. Con rods were balanced and fitted with ARP bolts.
The most meaningful upgrade during the rebuild was the replacement of the original Carrera 3.2 oil pump with a larger unit from the 996 Turbo, delivering significantly greater pressure and scavenge capacity and directly addressing the root cause of the seizure. Timing chains, rails and all drive gears were replaced. Every valve guide was renewed, all inlet valves replaced and a cracked exhaust valve renewed. Three-angle valve seats were recut and all valves lapped in. Springs, spring seats and spring heights were checked and corrected, the originals having been found to be incorrect on teardown.
Interlock rings were machined into both the cylinder heads and barrels, a precision modification creating a positive mechanical register between the two and preventing the relative movement that can cause head gasket failure under sustained high-load running. The engine was reassembled with new gaskets and seals throughout. The 3.2 was back, now stronger, better lubricated and more durably engineered than at any point in its history.
Engine Management: Electronic Performance Systems
Dave Rowe at Electronic Performance Systems built the electronics architecture around a MoTeC M84 ECU, a professional-grade engine management unit with 512K memory expansion and advanced functions enabled. The engine loom was manufactured by EPS using Spec44 wiring and DR25 sleeving, terminated at the ECU via a 61-pin Autosport bulkhead connector for clean, reliable signal transmission.
The sensor suite is comprehensive: dual Bosch LSU 4.9 wide-band lambda sensors via a MoTeC Lambda-to-CAN module; a 4-bar MAP sensor; oil pressure, fuel pressure and three oil temperature sensors; two air temperature sensors; a hall-effect throttle position sensor adapted for the 3.2 Carrera; and brake pressure sensors front and rear. A MoTeC C125 colour display and data logger, integrated with a GPS module via CAN bus, captures every lap for detailed post-session analysis.
Race Debut: 2023 and 2024
With the car fully homologated, the engine rebuilt and the electronics dialled in, the 903 made its competitive debut in the CALM All Porsche Trophy, run by the 750 Motor Club. A friendly, power-to-weight balanced, 100% carbon-offset Porsche-only series supporting the CALM mental health charity, it races across iconic British venues including Donington Park, Silverstone, Brands Hatch, Croft, Snetterton, Anglesey and Thruxton, as well as occasional international events at Spa-Francorchamps.
The 2023 season saw the 903 entered initially in the Roadsports Series and then the CALM All Porsche Trophy, accumulating race experience across Anglesey, Brands Hatch and Snetterton, and culminating in an extraordinary international outing at Spa-Francorchamps in October 2023. All of this was achieved on the original Paxton supercharger inherited from the car's American racing days.
The 2024 season brought further circuit knowledge alongside new challenges. A wheel and swingarm were badly damaged at the Croft season finale, requiring an extensive winter repair programme. More significantly, the Brands Hatch round in June revealed a new performance ceiling: excessive air intake temperatures under the heat of competition were limiting what the Paxton-supercharged engine could deliver. That observation set the direction for the most ambitious engineering phase yet.
2025: Rotrex Supercharger and Intercooler
The main development for the 2025 season was the replacement of the Paxton supercharger with a Rotrex C38-81 centrifugal unit: a modern Danish design with a self-contained traction fluid lubrication system, a peak impeller speed of 90,000 RPM and a pressure ratio capability of 2.85:1. Fifty years of engineering progress over the Paxton is evident in both the boost it delivers and the reduction in parasitic drivetrain loss. Critically, the Rotrex is efficient enough to drive charge air through an intercooler at useful boost pressures. The Paxton was not: its lower efficiency meant it could not sustain decent boost levels against the additional back-pressure of an intercooler, which is why none had been fitted during the 2023 and 2024 seasons.
A bespoke intercooler was therefore designed and built by Alpha Performance Fabrication alongside the new supercharger, engineered with a 4-inch-deep core and specified to support builds well beyond 600bhp, leaving ample headroom for future development. The Snow Performance water/methanol injection system, carried over from the original Paxton setup, was retained and fully integrated into the new combination. Capable of lowering charge air temperature by upwards of 20 degrees Celsius while simultaneously raising effective octane rating, it complements the intercooler and reduces engine sensitivity to detonation. Together, running a 70mm supercharger pulley, the Rotrex, intercooler and water/methanol system deliver up to 0.95 bar (circa 13.75psi) of intercooled boost within safe tolerances.
The new package was dyno-mapped by Dave Rowe at EPS on 18th April 2025, running a conservative 75mm supercharger pulley delivering 0.87 bar of boost. The results validated the approach. Three days later at Donington Park, the 903 took first place in the Invitation Class on a wet track, demonstrating that the new setup was not only more powerful but also more manageable in difficult conditions.
2025: Ignition Overhaul
During the April dyno session, Dave Rowe identified the ignition system as the next limiting factor. At higher boost levels and elevated revs, the existing setup could no longer deliver the spark energy required: misfires under load were masking the true potential of the new supercharger combination. The solution, specified and installed by EPS, was a Bosch Double Fire 3x2 coil pack paired with Bosch Motorsport three-channel ignition amplifiers, wired via Clewett Engineering 8mm silicone plug leads with abrasion and fire-resistant sleeving. The distributor was replaced by an Adapt Motorsport ignition sensor and reference module with a ZF Hall Effect sensor, providing clean and precise crank and cam signals to the MoTeC ECU.
The work was completed just in time for the Snetterton round in June 2025, which proved to be a breakthrough weekend. With the ignition now matched to the demands of the supercharged power unit, the 903 delivered its most composed and competitive performance to date across all three race formats, a clear demonstration of what the package was now capable of.
2025: Gearbox Development and Full Boost
With the power unit performing strongly through the second half of the 2025 season, attention turned to the drivetrain. In September 2025, the gearbox was stripped again for installation of the WEVO GateShift kit: a precision internal gate system machined using 3D design and investment casting technology that introduces positive detents, clear tactile feedback and controlled gear selection forces to the 915 transmission. The feel of the gearchange was transformed, echoing the precision of the later G50 gearbox and giving the driver far greater confidence under race conditions.
In October 2025, an FVD single-mass ultra-lightweight flywheel was fitted: a precision-machined and heat-treated billet steel unit weighing just 3kg. The reduction in rotational inertia delivered noticeably quicker acceleration, sharper throttle transitions and a more urgent climb through the rev range. That same month, the supercharger pulley was swapped from 75mm to 70mm, bringing the Rotrex impeller to its designed optimum of 90,000 RPM at 6,300 engine RPM. The result is the full 0.95 bar of intercooled boost the Rotrex was designed to deliver, and a reliable, sustained output of 425bhp: the complete capability of the 3.2-litre air-cooled engine and supercharger combination, now properly on song and proven under race conditions.
Heading into the 2026 season, two further upgrades complete the package. The jump to 425bhp places greater thermal demands on the drivetrain, so a dedicated gearbox oil cooling system has been added: a WEVO oil-out gearbox manifold routes oil from the transmission to a Mocal electric oil pump and a compact 16-row Mocal oil cooler mounted behind the right-side rear wing intake. Fully reversible and requiring no welding or machining of the 915 casing, it ensures the gearbox can sustain the increased load race after race. The braking system has received an equally significant upgrade. A Balance Beam Brake Pedal Assembly, as originally fitted to the 911 SC RS by Porsche, replaces the standard single-master-cylinder arrangement. Two brake master cylinders mounted in parallel on a purpose-built bracket allow precise mechanical distribution of braking force between the front and rear axles. This is complemented by a Remote Brake Bias Adjuster by Wildwood, allowing the driver to make fine front-to-rear bias changes from the cockpit while driving, ideal for adapting to changing race conditions. Power and braking now properly matched, the 903 heads into 2026 as the most complete version of itself yet.
The 903 now competes in the Invitation Class of the CALM All Porsche Trophy, holding its own against cars 40 years its junior. With the right people, the right vision and a refusal to cut corners, age is no barrier to performance.