From Mercedes-Benz press: During its 18-year "lifetime", which was not planned to last that long, but in the end was indeed successful, this SL got a whole series of six- and eight-cylinder engines. Its model designations accordingly are quite varied.
The eight-cylinder models were led by the 350 SL (1971 to 1980), whose 3.5-litre engine (M 116) already was known from the W 108, W 109 and W 111 series. The 147 kW which it delivered at 5800 rpm helped the SL, which did weigh 1600 kilograms after all, to clock nine seconds for 0 to 100 km/h and reach a top speed of 210 km/h. The 350 SLC had identical performance figures.
From autumn 1971 onwards the 450 SL also was produced. Its engine (M 117) developed an output of 165 kW at 5000 rpm. Top speed was 215 km/h, and it needed 8.8 seconds to go from 0 to 100 km/h. In 1972 the corresponding Coupé version, the 450 SLC followed, with identical engine and identical performance. Prior to March 1973, both were destined exclusively for export to North America; after that they were included in the general sales range.
In July 1974 the SL model range was extended: as a consequence of the oil crisis of 1973, the SL and SLC now were available as models 280 SL and 280 SLC with the 2.8-litre M 110 engine. It developed 136 kW at 6000 rpm and had proven its reliability in the two years before in the "Stroke Eight" series W 114/115 and in the W 116-series S-Class. Both models had identical performance: the top speed was 205 km/h; sprinting from 0 to 100 km/h in 10.1 seconds was possible.
So three SL engines now were available – nowadays nothing unusual, but in those days something new in the history of this model category. Only the attentive observer could distinguish between the three variants: The 280 SL could be recognized by its narrower tires in comparison to the 350 SL and the 450 SL. In addition, the 450 SL featured an inconspicuous front spoiler which was attached to the rear lower end of the front apron and distinctly increased the radiator's air throughput.
Between November 1975 and February 1976 the fuel injection systems of all three engines were changed for better compliance with the emission standards, which meanwhile also had become stiffer in most European countries. The electronically controlled Bosch D-Jetronic was abandoned for the newly developed mechanically controlled Bosch K-Jetronic. The changeover entailed minor losses in performance in all three cases: in the 280 SL to 130 kW at 6000 rpm, in the 350 SL to 143 kW at 5500 rpm, and in the 450 SL to 160 kW at 5000 rpm.
At the same time the compression ratios of the 2.8 and 3.5-liter engines were slightly reduced. The 3.5 and 4.5-liter engines additionally got a contactless transistorised ignition and hydraulic valve play compensation to facilitate maintenance.
The compression ratio of the 2.8-liter unit was raised to the old figure again in April 1978. With a few supporting measures the engine then regained its earlier power potential of 136 kW, but now already at 5800 rpm.
In September 1977 Mercedes-Benz launched the 450 SLC 5.0 with a V8 engine (M 117) enlarged to a displacement of five liters. A hidden innovation was the first-time application of hypereutectic cylinder contact surface machining, which made it unnecessary to insert cylinder liners. The engine delivered 177 kW at 5000 rpm, good for zero to 100 km/h acceleration in 8.5 seconds and a top speed of 225 km/h. The vehicle's bonnet and boot lid were made of aluminum, and it had light-alloy wheels as standard. On the outside the 450 SLC 5.0 was recognizable by, among other things, a narrow spoiler on the rear end.
At the Geneva Motor Show in March 1980 the SL and SLC presented themselves in updated form. The interior appointments including steering wheel were matched to those of the 126-series S-Class, and the engineering was brought up to the same level. The previous three-speed automatic transmission with torque converter was replaced with a four-speed variant. Models 280 SL and 280 SLC were given a five-speed manual transmission as basic equipment. In addition, the hardtop now was included in the standard specifications of the open-top variant. But above all the light-alloy eight-cylinder engines of the 126-series S-Class, slightly modified, made their arrival in the 107 series. The six-cylinder engine of the 280 SLC remained unchanged.
The new 500 SL, equipped with the 5.0-litre V8 (M 117) familiar from the 450 SLC 5.0, replaced the 450 SL and made an output of 177 kW at 5000 rpm available, to give the new top-of-the-range model a 0 to 100 km/h acceleration of 7.8 seconds and a top speed of 225 km/h.
Models 350 SL and 350 SLC were sent off into retirement after nine years of production. Their successors were the 380 SL and 380 SLC, whose 3.8-liter light-alloy engine (M 116), with 160 kW at 5500 rpm, originated after the pattern of the five-liter unit, by enlarging the bore of the long-serving 3.5-liter V8 with grey cast iron cylinder block. Both models attained top speeds of 215 km/h and needed nine seconds to go from 0 to 100 km/h.
From the outside the new models were almost indistinguishable from the previous models, except for the model plate. All three SL models now had a light-alloy bonnet and the discreet front spoiler familiar from the 450 SLC 5.0; the 500 SL also got a light-alloy boot lid with black plastic rear spoiler, already familiar from the five-litre Coupé.
In autumn 1981 both V8 engines were thoroughly redesigned in the context of the "Mercedes-Benz Energy Concept" to reduce their consumption and pollutant emissions. Along with an increase in compression ratio the measures comprised camshafts with changed valve timing, air-bathed injection valves, and an electronic idling speed control. Owing to the altered camshaft tuning the maximum torque could be shifted to a lower engine speed range and, in the case of the 3.8-liter engine, even increased. This power plant underwent particularly far-reaching changes: to get a more favorable volume-to-surface ratio the bore was reduced and the stroke increased. The modified 3.8-liter V8 thus had a slightly larger displacement. In both eight-cylinders, in exchange, so to speak, for the improved economy, minor losses in power had to be accepted, output dropping to 150 kW at 5250 rpm in the 380 SL and to 170 kW at 4750 rpm in the 500 SL. As in the 126 series the final drive ratio was adjusted to the changed engine characteristics and made higher, from 3.27 to 2.47 in the 380 SL and from 2.72 to 2.24 in the 500 SL.
For the SLC Coupés these changes came too late, however: at the Frankfurt International Motor Show in September 1981, along with the "Mercedes-Benz Energy Concept" the 380 SEC and 500 SEC models of the C 126 series were presented, spelling retirement for the SLC models, which had been built for exactly ten years.
But even after ten years of production no thought was being given to a replacement for the SL models. Four years after the Energy Concept was presented, they even came in for extensive refinements, and so in September 1985, again at the Frankfurt show, a completely revised SL model range was introduced. The emphasis was on a restructured engine range. A discreet facelift, primarily recognisable from the front spoiler and wheels with aluminium rims (diameter: 38.10 centimetres), was also part of the package. The front axle was done over and the brakes enlarged with fixed callipers. To prevent the cars from pulling to one side during braking, the steering offset was reduced.