PRESS Brit Pop

Article from Banzai Magazine August 2005

Words: Joe Clifford

Conceptually, Mazda's RX-8 Britcar competitor was only supposed to prove the reliability of rotary engines, but it also has a habit of winning races...

Last issue we reported on Mazda's Guglielmi Motorsport-prepared RX-8 achieving its first overall race win in the EERC Production S1 series at Snetterton circuit. Great news, and congratulations to drivers Nattasha Firman and Mark Ticehurst, but what intrigued me was the fact that of all the cars entered in this endurance race, the RX-8 was the closest to standard.

Apparently, the suspension, rolling stock and roll-cage are the only modifications. Was that actually the case, and is the RX-8 really so ideally suited to track use? I decided to visit Steve Guglielmi, proprietor of Guglielmi Motorsport (GM) in Daventry, to find out.

"The base car is very aerodynamic," Steve pointed out, "and the chassis is extremely rigid despite - or perhaps because of - the large door aperture."

The pillarless opening is a novel feature of the RX-8 and to retain the rigidity a B-pillar would normally provide, Mazda has engineered an extremely stiff surrounding shell. Ultimately, the extra stiffening provided by hefty chassis rails, strut braces and the need to carry up to 100 litres of fuel bumps up the kerb weight, blunting performance.

Standard, the RX-8s tip the scales at 1380kg, a figure which is quite normal for a car of this size. But after removing the underseal, seats, carpets, door cards etc the weight didn't fall off as expected.

EERC regulations require competitors to have a minimum weight of 950kg, yet no dietry programme was going to get a Production class RX-8 to that level (even the lightweight Clio Cup cars weigh nearly 1000kg), though for Snetterton GM managed to slim the car's weight to 1220kg. Stripping the bitumen-based soundproofing shed 60kg alone, while further savings were made by removing all carpeting, the majority of the air conditioning system (the radiator is retained to act as a guard for the engine radiator) and switching to lightweight OE size 8x18" Speedline Corse alloys. Steve has recently commissioned Scorpio Composites to make new carbon fibre doors, and these are hoped to bring the kerb weight down to 1180kg; even more when the glass windows are replaced with polycarbonate.

As far as possible, the RX-8's weight has been redistributed to compensate for a supplementary 50-litre fuel cell carried above the rear axle. The original 62-litre tank is retained, though its capacity has shrunk to 50-litres with volume displacement balls to achieve a 100-litre total fuel capacity. During the race, only 50 litres of fuel can be added at any one time, so the RX-8 runs an arsenal of five pumps to salvage every last drop of fuel before pitting. At this point the original plastic tank is immobilised because it was impossible for GM to modify it to accept 50mm diameter quick-fill nozzles. The supplementary cell is then brimmed and the car returns to the track with only a 50-litre load. Refining the fuel system has been one of the biggest challenges for the GM team. It's a phenomenally complicated setup with built-in pressure regulators and ECU-adjusted main pump voltage, not to mention the fact that it doesn't run a return fuel line to the tank.

Chassis-wide, Steve commented: "We learnt how well the RX-8 handled through Formula Woman. Apart from fitting a roll-cage, throughout that event the car was standard, and it was only at the final round that we decided to uprate the brake pads to Pro-Friction items." Why, I wondered? "The girls were trying so hard with the limited grip of standard road tyres. The ABS was constantly cutting in and depositing the softer standard pad material on to the discs in patches."

Endurance racing certainly requires uprated brakes, so GM has boosted performance by running 355x32mm Brembo discs on custom bells with four-pot Brembo OE-style calipers modified with race seals to handle the sustained high temperatures. The original master cylinder and servo are still in residence, though the calipers are soon to be replaced with custom Brembo four-pots. These calipers can accommodate 25mm-wide Pagid RS29 (orange) pads which should last an entire 24-hour race. The rear setup is OE-spec albeit with Pro-Friction pads.

Production S1 regulations also dictate the use of a control tyre manufacturer - Dunlop. Competitors then have free rein to choose a tyre grade from the entire range; GM has chosen 235/640 slicks. Using these instantly increases the levels of grip and lateral G, requiring an uprated suspension system to exploit this to its full potential.

Bilstein PSS9 coilovers with revised valving, Eibach springs and modified bump rubbers carry out the majority of work. The top front wishbones now feature polyurethane bushes and have been slightly offset to increase camber (now 4-5° all round to increase tyres' contact patch under cornering), while the lower arms use inserts which enable them to accept spherical bearings. Similarly, the rear suspension arms use standard links modified to accept spherical rod ends, plus GM is beginning to play around with the rubber joints to enhance passive rear-wheel steering. Combined with a stiffened OE-spec front anti-roll bar and FIA-spec roll-cage, the chassis can generate a stomach-churning 1.4G before breaking away.

Regulations on how power is produced may not be tight but there is an upper limit of 230bhp. Consering that the standard RENESIS rotary makes 231PS at 8200rpm (227.8bhp) there's very little margin for tuning. An ITG carbon fibre induction kit, sports catalyst, tubular manifold and BTB back box are the only modifications, though Steve admitted that having tested these on a dyno they've made no difference to the output. Most likely this is due to the RX-8's overactive ECU than a failing in the products themselves. So plans are afoot to install MoTeC (or similar) management, cap power at 230bhp, and consolidate the aftermarket goodies to increase mid-range torque. Engine power is delivered through the original six-speed gearbox via a modified clutch. The standard pressure plate remains but is joined by a Helix paddle centre plate on a lightweight Madzaspeed flywheel.

To say that this RX-8 is virtually standard stretches the truth, though by modifying as many OE parts as possible GM has only concentrated the car's essence. It may weigh more than the majority of its competitors but this obviously hasn't been too detrimental. The RX-8 has proved itself powerful, well balanced and robust enough to cope with prolonged abuse on track.

Mazda's concept of using a race series to prove rotary engine reliability has been conclusively proved, with the added bonus of race wins too. Perhaps a little of the magic which helped Mazda's 787B race car win Le Mans in 1991 has filtered down into the RX-8. Guess that's why it wears the same eye-boggling red and green colour scheme.