Road test -- Mercedes-Benz 300SL-24

Civil Service

As a Mercedes Benz badge is one of the most coveted in motoring, it seems appropriate that the same company should also offer the most envied suffix in premium price sports motoring: SL. The initials were first seen in 1952 and factory literature translated the appellation into English as “Sport Light”, a cross-reference to the “L” for lightweight tubular chassis and an inline six cylinder engine developed from that of the 300S.
That gullwing competitor and its 1954 production descendant eventually led to an appraisal of the commercial worth of selling a luxury sports car under the SL badge, a process which has been incredibly profitable even by Benz standards. The original gullwing series were far from rare beasts (the factory reports that “a total of 1400 gullwings were built”) and the commercialisation of that emotive SL badge has seen production by the thousands as routine: some 25,881 of the 190 SL were made from 1955-63 and 49,912 of its “pagoda” top 230/250/280 SL successor.

The car to bear the 300 SL badge today is a very different animal to the competitor of 1952, and is anything but lightweight at a kerbside 33.2 cwt, over 1.6 tons. There is a six cylinder, 3-litre, engine in the variant we tested. It has all the right power-producing credentials; fuel injection, DOHC, four valves per cylinder. However, it is hitched up to a 5-speed automatic with a kerb weight which means a power to weight ratio inferior to any mundane “hot hatchbacks.” The result is the finest of touring 2 + 2s, one that pampers its owner beyond belief (but not to the peaceful travel standards of Jaguar) and yet remains fun to hustle in ungentlemanly manner. Truly the 1989 debutante 300 SL-24 should be renamed 300 TLS, or “Touring Luxury Sport,” as comfortable speed is its apparent priority.

The UK Range

To exceed 150mph, a 1991-2 Mercedes SL customer must opt for the V8. Demand does seem slightly higher for these eight cylinder variants. A major London-based dealer dispelled all those “wait for two years, and may be you’ll to on the waiting list,” warnings. His brisk answer to our telephone query on delivery dates was: “we have November production availability of 300 SL, which means you can have one in January 1992, or December production availability for the V8s, which means February UK delivery.” Could we have any colour we like? “Certainly sir, you lay down the specification and it will be built to that schedule,” was the prompt reply. Mercedes is not alone in witnessing the decimation of waiting lists. We understand that “if you are not fussy about the colour,” a Lotus Elan can be “yours tomorrow” from one of the largest London Lotus outlets.

The basic range of Mercedes SL offerings in the UK comprises an SOHC 6-cylinder 300SL of 190 bhp at a sniff under £50,000 (49,960); the 300 SL-24v tested here at £54,460 and the 32-valve V8 of 326 bhp at a list £70,090. All SLs have automatic transmission as their standard fitment, but that of the test car was an optional (£723.37) 5-speed rather than the standard 4-speed. Showroom standard equipment on all SL models is headed by the aluminium hard top; we took delivery of the car in this form and then went back to Milton Keynes (at the request of the company) to make sure it was removed and stored efficiently whilst we enjoyed open air motoring for the majority of the week. Also included at these elevated list prices are electronic anti-lock braking; power assistance of steering, side glass mirrors, convertible top; rollover hoop; central locking; radio aerial (but not the radio/stereo entertainment unit itself; that is still left to the customer at unspecified extra cost). Small details such as walnut wood finishes and a first aid kit are also included.

Comprehensive though the showroom specification may seem – and the V8 incorporates items such as leather seating and metallic paint — our demonstrator demonstrated that the UK list price is virtually irrelevant. “Our” car cost £10,806.55p more than the list cost. Enough to buy quite a decently rapid small saloon.

Technical Analysis

First sketches and outline features for a new generation of SL convertible 2 + 2 coupes were rendered in 1979. At the time, a mid-engine layout was a distinct possibility (perhaps utilising the Wankel unit) but by 1982 the serious graft had begun. The company told us at the launch, “nearly 20 models, all to 1/5th scale, were built as the design emerged. Full sized clay, wood or plastic models were also built. The roof posed particular headaches, as the safety aspects of the new car were laid down in the original brief. One idea, later abandoned, was to have a finned roof with a rigid rollover bar. In all, 34 designs of roof were examined.”

The rakish but plump machine was created in its final form by 1985, complete with the rollover bar that automatically erects (prompted by a G-sensor that activates a spring within 0.3s if it detects an impact), or that can be retracted at leisure, using hydraulics. Even then an over-ride system will flick the rollover hoop into action if the sensor detects excessive lean. More mundane, but pleasing for many sporting owners, is a practical boot that has few rivals from the convertible classes.

The power units, as for the strut and multiple link suspension, were adapted from existing saloons. The 24-valve unit (M104) has been experienced by Motor Sport in the 300 CE and we admire this tough 7000 rpm unit considerably. The overhead camshafts are chain-driven, the crankshaft is of tempered steel and the undersides of the pistons received a cooling balm of oil sprayed from beneath. The cylinder head is a crossflow layout that utilises hydraulic valve tappets and an automatic camshaft timing adjustment system to promote good idle and mid-range torque, despite the high rpm capabilities of the unit. It operates an adjustment piston which alters camshaft timing (inlet only) via meshing teeth that are prompted from the engine management system through a magnet. A valve then forces engine oil to enact the timing changes, reducing overlap to “virtually” nothing at idle speed and progressively allowing overlap at middle range rpm, whilst inlet valve closure is delayed at peak rpm.

Action

The SL cockpit is not one to give away its secrets easily. It took us time to release the bonnet or free the handbook from the clutches of the centrally locked glovebox. The flip-top lids to the door compartments are so snugly fitted that we cursed the lack of cabin storage space, until these features had been more thoroughly explored. Add in an American style “hand brake”, one that actually operates on a high-stepping foot pedal, and it is easy to feel a stranger in a new Mercedes. Unless, as for so many buyers, you have owned one before. Or learned how to lever open safe doors as training for the hefty portals deployed by Unterturkheim.

Behind a steering wheel made more bulky by the optional air bag equipment, the five dials and their extensive orange calibrations are augmented by a digital outside temperature gauge and 15 warning lights. The seats are special for their mounting bases in magnesium, but do not offer extraordinary location of their occupants, especially in the magnificent array of optional leather facings. The writer is happier to perch upon cloth for practical and animal welfare reasons, but there was no denying the apparent perfection in trim standards throughout the cabin. We simply could not spot a single flaw in the fit and finish of the plastics, woolly carpeting, leather and walnut employed.

It is similarly hard to fault the driving experience, save an overall feeling that a “300 SL” should provide a little more explosive and emotive performance than a machine of this power to weight ration can possibly display. A precision 500 rpm tick-over is replaced by disciplined aggression to the note of the modest twin exhausts as 400 rpm is surpassed. By 6500 rpm, when the auto-box shifts from first to second, you have no doubt that a pedigree performance engine is working nobly to haul that substantial girth to greater velocities. We also checked performance using the full 7000 rpm permitted and manual changes of the otherwise totally unobtrusive automatic: there were slight gains, as noted in our performance panel, but the motor always had a zest that contrasted with unexceptional acceleration statistics for a £50,000-plus vehicle. In fact many of the SL speed statistics (0-60 and 0-100 mph) correlate within tenths of early performance test results returned on the Escort RS2000.

Our maximum speed ace – who carries the appropriate initials MPH – squeezed fractionally more mph from the 300 SL than we had seen recorded elsewhere. Yet the maximum recorded at Millbrook was still 6 mph shy of the publicity claim at 137 mph. As a driving experience, there was no doubting the safety and sheer adhesion of the SL chassis. Yet we were initially disconcerted to find the 225/55-section German Dunlops following the contours and cambers of all but the best in road surfaces. Meanwhile, the steering failed to self-centre and the ride was notably stiff between 20 and 35 mph, the ideal pace at which some clientele will be seen at maximum posing mode. Press a little harder and it is difficult not to be impressed by the sheer composure of the big machine under 50-80 mph pressures, especially those giant brakes – which resisted the ravages of performance research gallantly and effectively.

You can drive the SL hard for fun, and that is not something I would report of the BMW 850i or the Jaguar XJ-S. At least, not without enhancements such as M-Technic suspension or TWR/JaguarSport suspension settings respectively. The roofing arrangements allow you to experience a hardtop express, a civilised and swiftly power-operated convertible top, or the exhilaration of touring in the clean lines of an open-air car uncluttered by fussy roll cage. The success of the 300 SL is that it can adopt these roles successfully, almost becoming three cars wrapped in one expensive package. The 300 SL is a little less suave than a BMW 850i with the hardtop in place, but far more comfortable and wieldy than a Porsche 928 if you want to explore its cornering capabilities. Under such circumstances you appreciate the efficiency of individual heat/ventilation controls supplied on either side of the cabin. The soft top is motored into place amidst a whirring display of electronically motivated and controlled expertise which demands only that you stop the car before raising or lowering the top. The SL and its double-skinned roof are notably usable on rainy days in this form, but wind noise beyond 100 mph is markedly up on that of the hard top state. I can think of no more civilised convertible, top up or down; the total absence of rattles is also uncanny. When the roof is retracted, the nearest parallel I can think of is the BMW six-cylinder convertibles such as 325i, for they posses the same clean lines, but lack many MB features that could save your life, or that extend the car’s versatility.
Snags in use? Very few that are not products of its sheer bulk. The light roof lining cover is a tad impractical. The plastic lower cladding of the exterior is redolent of cheaper machinery and the tool kit is shoddily presented by comparison to BMW, but these are hardly items to deflect purchase.

Verdict

Mercedes makes SLs at the rate of 20,000 units a year in good times and that commercial success is deserved. The car is properly thought out and those who want more performance (albeit at the cost of fuel thirst) can always opt to spend £15,630 more on a V8. The SL may wear deceitful initials, but it is an honest automotive engineering achievement of solid worth. It promises enjoyable companionship of a kind that will motor through these recessionary times to resume its role as a creator of speculative queues. — JW

***

MOTOR SPORT TEST RESULTS — MERCEDES 300SL-24v

SPECIFICATION

ENGINE: Water-cooled, light-alloy block and DOHC 24-valve head, 6 cylinder in line; 4-valve per cylinder, inlet camshaft timing adjustment system. Capacity 2692cc (88.5 x 80.25mm). Electronic ignition and Bosch KE fuel management; 10:1 cr. Catalytic converter. Max power 231 bhp @ 6300 rpm. Peak torque 201 lb.ft @4600 rpm.

TRANSMISSION: Automatic 5-speed. Front engine, rear drive. Final drive 3.46:1.

GEAR RATIOS: First: 3.87; Second: 2.25; Third: 1.44 ; Fourth: 1.00; Fifth: 0.75 …..28.9 mph per 1000 rpm.

BODY: Steel and alloy (the latter 4.6% by weight) construction, open 2-seater, seats on magnesium bases. Spring-loaded automatic roll-over hoop action (0.3 second delay) or cockpit hydraulic actuation over several seconds; two doors. Electrically-operated soft top or 34kg/75lb steel hard top. Petrol tank of 80 litres/21.1 gallons.

DIMENSIONS: Wheelbase 99.0in/2515mm ; front track 60.3in/1532mm; rear track 59.9in/1521mm; width 71.3in/1812mm; length 176in/4470mm; height 50.5in/1293mm as a hardtop. Kerb weight 3718 lb/1690 kg.

FRONT SUSPENSION: McPherson struts, gas-filled strut damping and separate, inboard, coil springs; 30mm anti-roll bar. Steering; power-assisted recirculating ball, 3 turns lock-to-lock; 35.27 ft turning circle.

REAR SUSPENSION: Multiple (5 per side) links, coil springs and gas telescopic dampers in strut format; 13mm anti roll bar, weight-saving composites at attachment points.

BRAKES, WHEELS, TYRES: Vented 11.81in/300mm diameter front, solid rear, discs with four-piston steel calipers front, two-piston rear. Electronic anti-lock braking, ABS. Light alloy wheels, 8J x 16 Dunlop D40, 225/55 ZR16 test tires.

PRICE: £54,460 UK taxes paid. Options on test car: Metallic paint (£690.64); leather seating (£1019.62); memory seat adjustment (£939.84); memory electrical adjustment of seat and mirrors (£269.67); air bag restraints for both front seats (£2493.13); automatic transmission 5-speed (£723.37); electrically-adjustable steering column (£503.68); rear seats leather (£1258.47); air conditioning (£2270.21); seat heaters (£414.42); air shield to lower open air turbulence (£223.50). Total for press demonstrator: £65,266.55.

MANUFACTURER / IMPORTER: Mercedes-Benz (United Kingdom) Ltd, Mercedes-Benz Centre, Tongwell, Milton Keynes, Buckinghamshire, MK15 8BA.

CLAIMED PERFORMANCE: Max speed 143 mph (manual); 0-60 mph 8.3s (manual)

TEST RESULTS:
Conducted at Millbrook Proving ground using 1991 Correvit electronic measuring gear. Weather conditions: Dry, overcast
ACCELERATION: 0-30 mph 3.37 seconds; 0-40 mph 4.73 seconds; 0-50 mph 6.53 seconds; 0-60 mph 8.79 seconds (9.17) *; 0-70 mph 11.28 seconds ; 0-80 mph 14.45 seconds; 0-90 mph 18.11 seconds; 0-100 mph 22.91 seconds (24.85)*; 0-110 mph 29.86 seconds.
* automatic time, all others taken by manually shifting at 7000 rpm.

FLEXIBILITY: Third gear 50-70 mph 5.8 seconds; Fourth gear 50-70 mph 10.1 seconds; Fifth gear 50-70 mph 9.6 seconds.
Standing 0.25 mile/400 metres: 16.73 seconds @ 87mph (manual changes at 7000 rpm); 17.08 secs @ 85.6 mph (automatic changes @ 6500 rpm).
Maximum speed: Millbrook 2.029 mile bowl, 135.2 mph. Best observed speed 137.4 mph.
Maximum gear speed @ 7000 rpm: First 36.4 mph; Second 63.1 mph; Third 105.0 mph; Fourth 137.0 mph
Overall fuel consumption: Average 18.5 mpg, (95 RON cheaper unleaded). Test track 14.0 mpg.
Government mpg figures: Urban 19.3 mpg; @ 75 mph 26.6 mpg; @56 mph 31.0 mpg.