A LEGEND REBORN
POSSUM BOURNE’S HILL CLIMBER REBUILT
THE LEGACY LIVES ON, AS POSSUM BOURNE MOTORSPORT HAS REBUILT AND RESTORED POSSUM’S OLD WRC IMPREZA TO KEEP UP AND SURPASS THE BEST REPCO’S RACE TO THE SKY HAS TO OFFER
When you’re trusted to rebuild a car you’ve been around since its heyday, and you’re given free rein on the project’s final output and public perception — which direction do you take it? For Possum Bourne Motorsport (PBMS) owner and composite engineer Bryan Hayton, the decision was easy — the WRC-spec Subaru Impreza would stay period correct, but with some much-needed power and reliability improvements.
Originally built in 1998 by Prodrive, the WRC-spec Impreza was campaigned by Finn rally driver Juha Kangas, who crashed it during Rally New Zealand. The car was then purchased by Possum Bourne, who already had a WRC Impreza in competition, and decided to rebuild the crashed coupe to contest the 2001 Race to the Sky in Cardrona Valley.
There was nothing quite like the rebuilt WRC car contesting the mountain at the time — with around 447kW (600hp), Bourne won the event on his first outing. However, 2002 wasn’t as successful — a blown tyre cost the race.
After Possum’s passing in 2003, the Subaru was purchased by Vantage Doors and Windows (Vantage Motorsport) and used to contest Race to the Sky until 2007, driven by WRC driver Kenneth Eriksson, but it fell short of first place every year thanks to Nobuhiro ‘Monster’ Tajima’s mighty Escudo. Since Race to the Sky’s absence, the Subaru has been used for special events such as Rod Millen’s Leadfoot Festival in 2011 and 2012, driven by Emma Gilmour, and at the Possum Bourne Memorial Rally in 2013, driven
by Cody Crocker. So when the Repco Race to the Sky event was announced for 2015, Craig Vincent from Vantage swung into action, enlisting the PBMS team to do their thing and give the Subaru what it needed to return to the hill climb with a vengeance.
To be competitive, the team knew more power would be needed, but with a six-month deadline to combat Monster’s hill-climb-specific ‘ Super 86’, head engineer Paul Hayton started full time on the project, and out came the drawing board. The team discussed issues they previously had with the Subaru when contesting Race to the Sky — the first being a lack of power, but the main issue in the past had been cooling, as Paul explained. “For the last three or four years, we’ve had overheating problems. Because of how the intercooler and radiator had been positioned, the radiator wasn’t getting enough air to remain efficient.” For the Subaru’s most recent outing, the team cut large vents into the bonnet, and designed a big air dam on the front bar to help address cooling issues, but for Race to the Sky this could not be done, as Bryan decided the WRC-spec Subaru would retain the period-correct 2000spec bumpers and bonnet. “The problem we had initially was that the car had to look the same as it did in 2000. By making this decision, we couldn’t cut any of the car up, so we had to figure out a way to fit the large radiator and intercooler in there and make it work,” Bryan said, adding, “This was probably one of the biggest challenges of the build.” To combat this, the team designed a very clever V-mounted intercooler and radiator set-up which, along with a combination of air ducts designed in-house, works extremely well. With WRC oil coolers for both the gearbox and the engine installed ahead of each front wheel, ducting also had to be designed behind the 2000-spec bumper to channel air in the right direction.
With cooling under control, PBMS engine builder Glen Cox started building the PBMS-spec EJ20. “We decided to retain the factory engine capacity to help retain the period-correct theme we were going for throughout the rebuild,” Bryan explained. With a workshop full of WRC spares from the good old days, a Group A crankshaft was chosen, WRC engine bearings, and a bunch of PBMS-spec goodies such as the Argo PBMS-spec con rods, PBMS-spec JE pistons, PBMS 14mm head studs, PBMS-spec cams, and big-port cylinder heads — all bolted to, and inside, the PBMS ‘extreme power’ 2.0-litre block.
With a block now capable of handling their initial power goal, the team decided to make the switch from the Garrett turbo they previously ran, to a BorgWarner EFR 8374. The turbo sits up high on an easily removed slip-joint manifold, and boost control is taken care of with a TiAL 46mm external wastegate. “Another huge improvement we have made for both power and cooling is the use of Ethanol E85,” Paul told us. Not only is E85 cheaper than the old C16, it helps maintain cooler combustion temperatures — which the EJ20 desperately needed. “We upgraded the fuel system while we were at it, with new Bosch fuel pumps and Injector Dynamics ID2000 injectors to handle the E85,” Bryan explained. Once the PBMS team sorted out the fueling gremlins which slowed progress significantly in the final week of preparation (due to a restrictive fuel filter), the Subaru was tuned on the dyno with the MoTeC M880 ECU. The team were delighted to see their efforts pay off when the Subaru churned out 636kW (854hp) at the engine on 42psi of boost — 75kW more than the initial goal.
Back in 1998 when Prodrive initially built the Subaru, they definitely got the chassis, driveline, and suspension package right, as none of these areas needed upgrading before Race to the Sky 2015. The Prodrive Hewland WRC six-speed dog box is said to be the weakest link at the moment, which considering it was developed for a car outputting 220kW (300hp) originally is fairly impressive — mind you, you’d hope so for $90,000 back in 2000.
What Possum Bourne Motorsport has achieved in such a short time is astonishing — to have a vehicle performing like a modern hill-climb supercar and appearing as if it rolled out of the Prodrive factory in 2000 really is admirable. With Colin McRae’s younger brother, Alistair, piloting the Subaru at Race to the Sky 2015, we think the PBMS-built Vantage Motorsport Subaru has a real shot this year — watch out Monster, PBMS has come prepared.