Overview
The 903 enters the 2026 CALM All Porsche Trophy season as the most comprehensively developed version of itself yet. Following an intensive winter programme, the car carries a series of targeted upgrades designed to translate its 425bhp potential into consistent, reliable performance across a full season of racing.
The powertrain package is complete: the Rotrex C38-81 supercharger running a 70mm pulley and the bespoke Alpha Performance Fabrication intercooler together deliver 0.95 bar of intercooled boost and 425bhp within safe tolerances. That figure is in race trim: injecting water or methanol into the intake is not permitted within 750 Motor Club racing, so the Snow Performance water/methanol injection system is switched off on track and the engine runs an alternative map. To keep the drivetrain properly balanced at this power level, a dedicated gearbox oil cooling system has been added, routing oil through a Mocal pump and 16-row cooler mounted behind the right-side rear wing intake. The gearbox can now sustain race loads without thermal compromise.
The braking system has been brought up to the same standard. A Balance Beam Brake Pedal Assembly, as originally fitted to the 911 SC RS by Porsche, replaces the previous single-master-cylinder setup. Two brake master cylinders in parallel allow precise mechanical distribution of braking force front to rear, complemented by a Wildwood remote brake bias adjuster operable from the cockpit while driving. For the first time, braking capability is fully matched to the power available.
One unfinished piece of business heading into the season was the engine mapping. With so many changes to the powertrain over the winter, a full remap by Dave Rowe at EPS was essential before the car could be run safely at increased boost. Scheduling meant this critical work could not be completed before the opening round, and the decision was made to miss Croft entirely rather than race before the car was properly mapped.
Round 1: Croft Circuit, 11th & 12th April 2026
With the revised powertrain package in place, a new engine map was required before the car could be run at increased boost. The mapping could not be completed in time for Croft, so the round was sat out. A frustrating start, but the right call.
Round 2: Donington Park National Circuit, 30th May 2026
The second round of the season took place at Donington Park, where the CALM All Porsche Trophy was welcomed as a guest of the Historic Sports Car Club for its annual Spring Trophy, with the 903 entered for two 20-minute sprint races. Although the simulator preparation had been built around the full Grand Prix circuit, it became clear on the day that the races would run on the shorter National Circuit, calling for a rapid rethink of the final chicane. With the engine mapping completed by Dave Rowe at EPS on 20th May, just ten days before the race, it was the first true opportunity to run the 903 at its full 2026 specification, and the car responded with the fastest lap time of its racing career, a 1min25.115secs set in qualifying. A split bushing in the gear lever rod then robbed the car of fifth gear for both races, a frustrating fault but one external to the gearbox itself and straightforward to remedy ahead of Snetterton.
Round 3: Snetterton 300 Circuit, 20th & 21st June 2026
Round 3 took the 903 to Snetterton in Norfolk for the fullest programme of the season so far, with qualifying, two 15-minute sprint races and a 40-minute race with a mandatory pit stop, all run on the long "300" layout. The Donington gear selection fault had been cured, Phil Brough confirming the cause as a split bushing in the gearshift linkage and replacing it in time for the weekend. Any optimism was short lived. The car developed persistent clutch slippage under load and had to be nursed around below its peak torque revs, producing a best lap of 2mins20.921secs in Race 2, more than four seconds off the 2mins16.711secs set on the same circuit in June 2025. By the 40-minute race the clutch was slipping at every gear change and the pace fell away by another five seconds a lap. The Invitation Class win was salvaged, but for the second weekend running the result was decided by the driveline rather than the engine.
Round 4: Brands Hatch Grand Prix Circuit, 12th July 2026
Round 4 brought the season's breakthrough. Racing on the full Grand Prix circuit in a single 40-minute race with a mandatory pit stop, as a guest of the Historic Sports Car Club at its annual Legends of Brands Hatch Superprix, in a venue marking its own centenary and in the return of the UK heatwave, the 903 finally showed what the 2026 specification can do. The torsion-sprung SACHS Racing clutch disc fitted by Phil Brough days earlier held firm, and with the full 425bhp usable at last the car recorded a best lap of 1min46.862secs, a new record for the 903 at Brands Hatch and more than five seconds quicker than the 1min52.077secs set on the same circuit in June 2024. Starting from the back of the field after a steady qualifying session, the drive through the field earned not only another Invitation Class win but, for the first time ever, the Driver of the Day trophy.
Round 5: Silverstone International Circuit, 16th August 2026
Silverstone was missed. The 915 gearbox rebuild that followed Brands Hatch was still in progress, with the casing away at the machinist. The front "nose cone" housing was being machined to route the oil feed for the new internal spray bar, and with the casing on the bench anyway the bell housing was also receiving a throw-out bearing guide tube update: the original guide tube is machined off and a custom steel tube fitted, retained from inside the differential case with a snap ring and sealed with the factory o-ring, allowing the late style 915 main shaft seal to be used on an early '72 to '75 transmission. Another round lost to the driveline, but the work is being done once and done properly.
Round 6: Castle Combe Circuit, 30th August 2026
Castle Combe was a late addition to the calendar. An invitation to race at the popular and well-supported Castle Combe Midsummer Mania Raceday was an unexpected treat for the CALM All Porsche Trophy, and the teams received a great welcome on the series' first ever visit to the fast, flowing and scenic Wiltshire circuit. Unfortunately, with the gearbox rebuild still mid-flight, it was not possible for the 903 to take part.
Round 7: Thruxton Circuit, 26th September 2026
Round 7 takes the 903 to Thruxton in Hampshire, the fastest circuit in the UK and one the car has never raced. It is an old school drivers' circuit of long, bumpy, high speed sweepers where commitment, smooth inputs and car set-up count for everything, and Phil Brough, who knows it well, is already walking through it section by section. Preparation is under way on a new Fanatec simulator rig, running the real Thruxton layout and a 1974 911 3.0 RSR whose power delivery is a fair stand-in for the 903, with the 1min30secs barrier already broken. With the gearbox rebuild now complete, the car will be ready.