Feb 8

Feb 8 Guide: Mercedes-Benz W297 CLK GTR Strassenversion

Mercedes-Benz - Mercedes-Benz CLK GTR - 1990s German Cars - 1990s Supercars - 1990s Homologation Cars - GT1 1994-1998

Background

After Mercedes-Benz abandoned sports car racing at the end of 1991, they focused on the Deutsche Tourenwagen Meisterschaft (DTM) which, from 1993, was contested by highly modified Class 1 Touring Cars.

In 1993, Mercedes expanded their motor sport programme to include a Formula 1 collaboration with Ilmor Engineering and Sauber.

Ilmor were then bankrolled to produce a Mercedes-badged CART engine for Penske to use in 1994.

1995 saw the Ilmor F1 engine re-branded as a Mercedes unit and the German firm began a 20 year collaboration with McLaren.

For 1995, the manufacturers that entered the ten round DTM in Germany (Mercedes, Opel and Alfa Romeo) also took part in the new 14 round FIA International Touring Car Series (ITC). The DTM and ITC merged for 1996, but when Opel and Alfa Romeo quit at the end of 1996 (owing to rising costs), the 1997 series was cancelled.

The DTM did not return until 2000.

In the absence of the DTM / ITC for 1997, Mercedes decided to contest the inaugural FIA GT Championship which was replacing the successful BPR Global GT Series that had taken place between 1994 and 1996.

Domestic rivals Porsche had entered the BPR Championship with a works team in late 1996. Meanwhile, BMW supplied the engines in the all-conquering McLaren F1s.

For 1997, BMW’s involvement would be stepped up a notch; their Italian satellite team, Bigazzi, were contracted to campaign a trio of semi-works F1 GTRs under the colours of long-term sponsor, Fina.

With Mercedes arrival, the stage was set for an epic battle between three of Germany’s biggest manufacturers.

Between 1994 and 1996, the BPR organisers had run their competition with a supplement to the Appendix J regulations that disregarded its official 25 car homologation requirement. To stimulate entries, only one road-going version had to be built before a car could compete in the BPR series. The Le Mans governing body (the ACO) followed suit.

For 1997, the FIA, who were now running the show, dropped the rule supplement and reintroduced the 25 car homologation requirement. It meant that Porsche and Mercedes would both have to build 25 road-going iterations of their GT1 contenders in order to compete.

McLaren had already met the production requirement and were able to produce an Evolution variant (the long tailed F1 GT) which would form the basis of their updated 1997 model.

However, to encourage manufacturer participation, the FIA decided to effectively assist Porsche and Mercedes by changing the terms of homologation; so long as one road car had been completed, the balance of production did not have to begin until twelve months after the season had ended.

Previously, homologation had always required a qualifying car meet its production criteria before it could go racing.

Unlike McLaren, whose F1 had been designed first and foremost as a road-going machine, Porsche and Mercedes decided to build out-and-out racing cars that were then reverse engineered for road use. This gave the two German firms a big advantage over their British rival.

Mercedes subsidiary AMG were commissioned to create the new W297 GT1 car. It was dubbed the CLK GTR and, thanks to its front and rear lights, bore a striking resemblance to Mercedes’ new-for-1997 W202 CLK.

Unsurprisingly, with what was a thinly veiled sports prototype, Mercedes won the 1997 FIA GT Championship for Drivers and Manufacturers. It had though been a close run affair with McLaren who decided to quit at the end of the season.

A further uprated Evolution model, the CLK LM, was then introduced mid way through 1998 and Mercedes took both titles for the second year in succession.

By this time, manufacturer support had dropped off a cliff; as a result, GT1 cars were banned from 1999 when GT2 machinery took over.

Despite the fact GT1 cars were no longer current, Mercedes still had the job of producing the required number of road-going CLK GTRs in order to retain their 1997 and 1998 titles.

Following the completion of a prototype street variant in 1997 (homologation of which was approved on April 1st), the rest of the road cars were assembled between late 1998 and mid 1999. Construction was a joint project between AMG and HWA Engineering.

HWA was established by AMG founder, Hans-Werner Aufrecht, to develop and build vehicles and components for Mercedes-AMG.

AMG had first signed a cooperation agreement with Mercedes in 1990. Mercedes then took a controlling interest in 1999, at which point HWA was formed.

Prior to the run of 25 machines required for homologation, AMG and HWA built another prototype (this time a production-spec. machine with additional road niceties that had been absent from the 1997 example).

A further 26 CLK GTRs were then completed between 1998 and 1999. 20 were Coupes and six were Roadsters.

The Coupes retailed at $1.547m, which made them the most expensive cars available at the time.

Chassis

Each CLK GTR road car was based around an identical carbonfibre and aluminium honeycomb monocoque to the GT1 version.

The tub was designed by AMG and built by Lola Cars in England. It had a wheelbase of 2670mm and an integrated roll cage made of 40mm diameter steel tube.

Suspension was via double wishbones with inboard pull-rod actuated coil spring / damper units and anti-roll bars at either end. The front suspension was bolted directly to the tub. The back end was attached to the transmission casing. The engine was mounted on an alloy subframe bolted to the rear bulkhead.

Cross-drilled and ventilated disc brakes had a 355mm diameter and four piston calipers at the front. 330mm discs with six piston calipers were fitted at the rear.

To make them more tractable for road use, the cars built after the initial 1997 prototype came with ABS, traction control and power steering.

The pneumatic jacking system from the GT1 variant was retained.

18-inch diameter wheels measured 10.5-inches wide at the front, 12-inches wide at the rear and were shod with Bridgestone tyres.

A 100-litre fuel tank used by the prototype was reduced to 90-litres for production.

Engine / Gearbox

In the engine bay was a GT 112 variant of the Mercedes LS600 engine.

Developed by Ilmor, it was an all-alloy naturally aspirated 60° V12 with dual overhead camshafts and four valves per cylinder.

Unlike the race version, which came with a six-litre engine as per the GT1 rules, the production-spec. road cars were fitted with seven-litre power units and no FIA-mandated air restrictors.

Bore stayed at 89mm, but stroke was extended from 80.2mm to 92.4mm which resulted in a 911cc gain. Displacement went from 5987cc to 6898cc.

Compared to the V12s used in other Mercedes of the era, the CLK GTR engine was dry-sumped and fitted with a host of special parts to include forged pistons, titanium con rods, a lightweight flywheel, enlarged valves and faster cams. The cylinder head covers and sump casing were magnesium and a carbonfibre engine oil tank was installed.

The compression ratio was 10.5:1.

HMS7.0 fuel-injection was supplied by Bosch.

Peak output was 612bhp at 6800rpm and 572lb-ft at 5250rpm.

Although an X-Trac six-speed sequential gearbox was retained for production, it was converted to paddle shift actuation and a foot clutch was added to extend the rebuild interval. Transmission was via a four-plate carbon fibre clutch and Quaife limited-slip differential.

Bodywork

The CLK GTR was cloaked in a carbonfibre body that featured the lights and front grille from the W202 CLK.

Among the car’s most attention-grabbing details were dihedral butterfly doors, a large roof scoop and an adjustable rear wing. Unlike the GT1 race version, the spoiler used on the road-going Coupe was integrated with the rear body; in high downforce mode, an additional 35° of rake was added.

Most of the myriad cooling solutions were found on the skirts and aprons.

The 20 production Coupes that followed the two road car prototypes were numbered 01/25 to 20/25.

Cars 21/25 to 25/25 were Roadsters of which a sixth example was also completed.

The Roadsters were completed after the Coupes. They came with a new engine cover, rollover hoops behind each headrest and a twin pylon rear spoiler similar to the GT1 race version.

Roadster front grilles featured a large three-pointed star whereas the Coupes had an unbranded grille with separate freestanding Mercedes emblem above. The wing mirrors (sourced from the regular CLK) were moved from the tops of the front fenders back to the doors. No roof of any description was supplied.

Interior

Inside, the cockpit was cramped, noisy and offered poor visibility.

Mercedes raided their parts bin for the dash and much of the switchgear.

Airbags were supplied for driver and passenger. The four-spoke steering wheel was removable.

As there was no luggage space at the front or back of the car, storage bins were added underneath each door.

Production cars 01/25 to 25/25 were numbered on the dash, centre console and door sills.

Alcantara was used to upholster the dash, steering wheel rim and the roof. The seats, door panels and rear bulkhead were leather.

As the bucket seats were attached to the rear bulkhead, the pedals were adjustable instead.

Carbonfibre inserts were applied to the doors and centre console.

Standard equipment included a CD player, four-point harnesses, electric windows and electric mirrors.

Options

Optional extras included air-conditioning and a seven-piece luggage set.

Weight / Performance

Because of the equipment added to the production GTRs, weight rose from 1005kg to 1470kg.

The Roadster weighed another 105kg on top.

Mercedes quoted a top speed of 199mph for the Coupe and a 0-62mph time of 3.6 seconds. However, in terms of its ability as a functional road car, the CLK GTR was heavily criticised.

Production Differences

The two road car prototypes did not come with numbered plaques as per the subsequent production run.

Most CLK GTRs were painted silver. The exceptions were Coupes number 17 (red), 19 (dark blue) and 20 (black) plus Roadsters 21 (black) and 22 (dark silver).

The first prototype along with production Coupes 5, 7 and 13 had tartan interiors. Roadster 22 was completed with a magenta leather interior. All the others were dark grey.

Coupe 13 and Roadster 22 were built for the Sultan of Brunei in right-hand drive. The remaining cars were left-hand drive.