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By 1955, Mercedes-Benz Technical Director Prof. Fritz Nallinger and his team held no illusions regarding the 190 SL's lack of performance, while the high price tag of the legendary 300 SL supercar kept it elusive for all but the most affluent buyers. Thus Mercedes-Benz started evolving the 190 SL on a new platform, model code W 127, with a fuel-injected 2.2 liter M180 inline-six engine, internally denoted as 220 SL. Encouraged by positive test results, Nallinger proposed that the 220 SL be placed in the Mercedes-Benz program, with production commencing in July 1957.
However, while technical difficulties kept postponing the production start of the W 127, the emerging new S-Class W 112 platform introduced novel body manufacturing technology altogether. So in 1960, Nallinger eventually proposed to develop a completely new 220 SL design, based on the "fintail" W 111 sedan platform with its chassis shortened by 30 cm (11.8 in), and technology from the W 112. This led to the W 113 platform, with an improved fuel-injected 2.3 liter M127 inline-six engine and the distinctive "pagoda" hardtop roof, designated as 230 SL.
The 230 SL made its debut at the prestigious Geneva Motor Show in March 1963, where Nallinger introduced it as follows: "It was our aim to create a very safe and fast sports car with high performance, which despite its sports characteristics, provides a very high degree of traveling comfort".
The W 113 was the first sports car with a "safety body," based on Bela Barényi's extensive work on vehicle safety: It had a rigid passenger cell and designated crumple zones with impact-absorbing front and rear sections built into the vehicle structure. The interior was "rounded," with all hard corners and edges removed, as in the W 111 sedan.
The W 113 was also the first Mercedes-Benz with radial tires.
Production of the 230 SL commenced in June 1963 and ended on 5 January 1967. Its chassis was based on the W 111 sedan platform, with a reduced wheelbase by 30 cm (11.8 in), recirculating ball steering (with optional power steering), double wishbone front suspension and an independent single-joint, low-pivot swing rear-axle with transverse compensator spring. The dual-circuit brake system had front disc brakes and power-assisted rear drum brakes. The 230 SL was offered with a 4-speed manual transmission, or an optional, very responsive fluid coupled (no torque converter) 4-speed automatic transmission, which was popular for US models. From May 1966, the ZF S5-20 5-speed manual transmission was available as an additional option, which was particularly popular in Italy. Of the 19,831 230 SLs produced, less than a quarter were sold in the US.
The 2,308 cc (2.3 L) M127.II inline-six engine with 150 PS (110 kW; 150 hp) and 196 N·m (145 lb·ft) torque was based on Mercedes-Benz' venerable M180 inline-six with four main bearings and mechanical Bosch multi-port fuel injection. Mercedes-Benz made a number of modifications to boost its power, including increasing displacement from 2,197 cc (2.2 L), and using a completely new cylinder head with a higher compression ratio (9.3 vs. 8.7), enlarged valves and a modified camshaft. A fuel injection pump with six plungers instead of two was fitted, which allowed placing the nozzles in the cylinder head and "shooting" the fuel through the intake manifold and open valves directly into the combustion chambers. An optional oil-water heat exchanger was also available.
A brief chronology of the most notable changes made to the 230 SL:
10/1963: First 230 SL with automatic transmission.
09/1964: Spare tire well removed, tire mounted horizontally.
11/1964: Optional tinted/thermal glass and new soft-top with steel bows (distinguished by missing chrome trim on the outer trailing edge).
04/1964: US models with radio Becker Europa TR instead of Europa TG.
08/1965: Some harmonization with new W 108/W 109 sedans, incl. new floor panels, combined brake and clutch fluid reservoir, trunk light and interior changes. US models with hazard lights.
03/1966: Mounts for three-point seat belts added.
05/1966: Optional ZF 5-speed manual transmission; rare and now very desirable.
The 250 SL was introduced at the 1967 Geneva Motor Show. Production had already commenced in December 1966 and ended in January 1968. The short one-year production run makes the 250 SL the rarest of the W 113 series cars. The 250 SL retained the stiffer suspension and sportier feel of the early SLs, but provided improved agility with a new engine and rear disc brakes. Range also improved with increased fuel tank capacity from 65 L (17.2 US gal) to 82 L (21.7 US gal). Like its predecessor, the 250 SL was offered with a 4-speed automatic transmission, and 4-speed or ZF 5-speed manual transmissions. For the first time, an optional limited slip differential was also available. Of the 5,196 250 SLs produced, more than a third were sold in the US.
The main change was the use of the 2,496 cc (2.5 L) M129.II engine with 6 mm (0.2 in) increased stroke, 2 mm (0.1 in) increased valve ports, and seven main bearings instead of four. The nominal maximum power remained unchanged at 150 PS (110 kW; 150 hp), but torque improved from 145 lb·ft (197 N·m) to 159 lb·ft (216 N·m). Resiliency also improved with a new cooling water tank ("round top") with increased capacity from 10.8 L (2.9 US gal) to 12.9 L (3.4 US gal), and a standard oil-water heat exchanger.
The wider power band of the 250 SL resulted in noticeably improved performance, as the 230 SL engines rarely produced more than 143 PS (105 kW; 141 hp) in practice.
The 250 SL also marked the introduction of a 2+2 body style, the so-called "California Coupé", which had only the removable hardtop and no soft-top: a small fold-down rear bench seat replaced the soft-top well between passenger compartment and trunk. The lacking soft-top relegated open California Coupés to a formidable nice weather ride, so many of them are very well preserved today. Retrofitting the soft-top above the rear bench seat requires considerable effort and expense, however. Thus while these 2+2 models are rare, their somewhat limited usability makes them not particularly sought after today.
In August 1967, a number of additional changes were incorporated to accommodate stricter safety regulations and US emission laws. The safety improvements included a collapsible steering wheel and padded wheel hub, concave control knobs, elastic black rubber heater levers (instead of rigid colored translucent plastic), and softer, rounded dash top padding. Door handles, locks, and window cranks were modernized and less protruding, the door pockets were elastic, the rear-view mirror frame was chrome instead of black plastic, and the side view mirrors became more angular. Essentially, the 1967 250 SL retained the more classic "chrome" interior of the 230 SL, whereas the 1968 250 SL introduced the modernized "safety" interior of the 280 SL.
US models acquired side reflectors on the fenders, Kangol three-point seat belts, an illuminated gearbox for the automatic, and emission control equipment. The chrome horn ring was changed to matte finish.
The 280 SL was introduced in December 1967 and continued in production through 23 February 1971, when the W 113 was replaced by its successor, the entirely new and substantially heavier R107 350 SL. Over the years, the W 113 evolved from a sports car into a comfortable grand tourer, and US models were by then usually equipped with the 4-speed automatic transmission and air conditioning. Manual transmission models came with the standard 4-speed or the optional ZF 5-speed, which was ordered only 882 times and thus is a highly sought-after original option today. In Europe, manual transmissions without air conditioning were still the predominant choice. Of the 23,885 280 SLs produced, more than half were sold in the US.
The main change was an upgrade to the 2,778 cc (2.8 L) M130 engine with 170 PS (130 kW; 170 hp) maximum power and 180 lb·ft (244 N·m) maximum torque, which finally gave the W 113 adequate power. The performance improvement was achieved by increasing bore by 4.5 mm (0.2 in), which stretched the limits of the M180 block, and required pairwise cylinder casts without cooling water passages. This mandated an oil-cooler, which was fitted vertically next to the radiator. Each engine was now bench-tested for two hours prior to being fitted, so their power specification was guaranteed at last.
The M130 marked the final evolution of Mercedes-Benz' venerable SOHC M180 inline-six, before it was superseded by the entirely new DOHC M110 inline-six introduced with R107 1974 European 280 SL models. For some time, it was also used in the W 109 300 S-Class, where it retired the expensive 3 liter M189 alloy inline-six.
A brief chronology of the most notable changes made to the 280SL:
12/1967: One piece wheel-covers (like W 108/W 109 sedans).
10/1968: US models with sealed beam headlights without fog lights.
02/1969: New tail lights with amber turn signals.
05/1969: ZF 5-speed manual transmission discontinued as listed option and available only on special request.
07/1969: US models with headlight assembly with full amber lower section, illuminated side markers, transistorized ignition, and improved emission control.
08/1969: Heated rear window for hardtop, hazard lights for all models, single master key for all locks.
04/1970: Bosch Lichteinheit headlights optionally with halogen main beam (distinguished by "flat" instead of "bubble" lens).
08/1970: Fuchs alloy wheels available as a factory-fitted option.
11/1970: Opaque beige plastic coolant expansion tank (instead of satin-black steel). New door locks: cylinder can be depressed while door is locked.
North American models have a number of subtle differences, the most obvious one being the distinctive "sealed beam" bulb headlights required in the US versus the Bosch Lichteinheit headlights for the rest of the world. 1970 US models also acquired amber turn-signal lenses on the rear lights, later than most other countries.
Other differences of the North American models include imperial gauges, chrome bumper guards, side reflectors (illuminated from 1970), lower rear-axle ratios for faster acceleration yet lower top speeds, and no "single-side" parking lights. US market 280 SL engines required emission control modifications, including "softer" valve timings, a reduced compression ratio and a modified injection pump, which reduced power from 170 PS (130 kW; 170 hp) to 160 PS (120 kW; 160 hp).
European cars were popular as US gray-market imports: those vehicles were brought to the US some years after their original delivery in Europe. Early European imports had aftermarket hazard lights and Kangol seat belts fitted, US safety requirements that were adopted in Europe only in later production years.
While the original design by Paul Bracq is regarded as a masterpiece today, it was more controversial at the time of its introduction. So in 1963, Pininfarina asked the Mercedes-Benz board to produce its own custom-bodied version of the 230 SL. Pininfarina's Tom Tjaarda turned the roadster into a fixed-head coupe that vaguely resembled the Ferrari 250 GT Lusso. He retained the grille and headlamps of the original, but raked the grille more sharply, sculpted the wings, and made the sides more bulbous and thus wider, while making the engine hood narrower and shorter. The rear was reminiscent of the Ferrari 330 GT 2+2 (also a Tjaarda design), but without taking away the distinctive personality of the 230 SL. Inside, Tjaarda left the dashboard unchanged, but the interior as a whole exuded the stamp of elegant Italian hand craftmanship. The result was appealing but not convincing enough to go into production and remained a one-off, subsequently acquired by German press baron Axel Springer.
Mercedes-Benz Chief Engineer Rudolf Uhlenhaut liked pushing the power envelope of his cars. In 1965, he fitted a 250 SL with the massive 6,332 cc (6.3 L) 250 PS (180 kW; 250 hp) M100 V8 engine from the Mercedes-Benz 600. This engine conversion gave the car, denoted as W 113/12, impressive power, but made it very front-heavy, so that this direction was abandoned. The car was eventually destroyed, the usual procedure for test vehicles at the time.
In 1966, the Turin coachbuilder Pietro Frua, a prominent car designer in Italy in the 1960s, presented a coach built 230 SLX Shooting Brake version of the 230 SL.
In 1968, Mercedes-Benz fitted a 280 SL with a 206 PS (152 kW; 203 hp) M50F Wankel engine, denoted as R 113 W 33-29. With a top-speed of 205.1 km/h (127.4 mph), a 0-60 acceleration of 8.7 seconds, and almost inaudible compared to regular SLs, it provided quite a surprise encounter for their owners in southern Germany at the time.
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