The 250SL was in a sense an interim model: In late 1967, Mercedes switched from the M129 six to the bigger M130, also used in the latest W108/W109 sedans. The new engine retained the M129’s stroke, but had re-spaced bore centers, allowing the bore to be expanded from 82 to 86.5 mm (3.23 to 3.41 inches) for a displacement of 2,778 cc (170 cu. in.). Adding this engine to the roadster created the third and final iteration of the W113 platform: the Mercedes 280SL.
The new engine’s additional power and torque were blunted somewhat by the W113’s steadily increasing weight, which now approached 3,200 lb (1,450 kg) with automatic and power steering, but the 280SL was nonetheless the quickest W113. With 23% more torque than the original 230SL, an automatic 280SL was now capable of 0-60 mph (0-97 km/h) times in the mid-9s, although top speed was little changed, limited mainly by gearing. The ZF five-speed was still nominally available, but not common. It disappeared from U.S. options lists in 1970, although it was catalogued in Germany to the end of production.
Depending on your point of view, the 280SL felt either more mature or a trifle lazier than the early 230SL. The suspension was also noticeably softer (thanks in part to the adoption of rubber suspension bushings to reduce the need for chassis lubrication), although by this point nobody except the occasional errant journalist expected the W113 to drive like a Corvette. The engine was less eager to rev as well, although with an extra half-liter of displacement, there was also less need to.
One might have expected that by 1969 the W113 would be in its declining years, especially considering that the exterior styling had changed almost not at all in more than five years, but based on the sales figures, the SL had found its niche. 1969 production topped 8,000 units — not a lot in absolute terms, but more than double the total 1955–1963 production of both the 300SL coupe and roadster.
One reason for the 280SL’s continued strong sales was that by the late sixties affluent American buyers were discovering Mercedes in growing numbers. In 1964, toward the end of Daimler-Benz’s distribution relationship with Studebaker, Mercedes sold around 11,000 cars in the U.S.; by 1970, Mercedes-Benz of North America was approaching the 30,000-a-year mark. The 280SL represented a relatively small fraction of that total, but was something an intrepid dealer could sell to a customer who already had a Mercedes 300SEL or wanted to show up their golf partner’s 280SEL 3.5 coupe. Such buyers appreciated the W113’s build quality and durability and were not troubled by its high maintenance costs and other minor foibles.
QUEST FOR POWER
Despite the Mercedes W113’s growing popularity, there was obvious room for improvement. The M130 engine still didn’t have an abundance of torque and was not especially quiet when pushed. In a drag race, the 280SL wasn’t far behind comparably priced American personal luxury coupes like the Cadillac Eldorado or Lincoln Mark III, but extracting such performance required more screaming 6,500 rpm manual upshifts than the average Mercedes owner was likely to tolerate. The automatic transmission, now ordered by more than 60% of customers, was short on finesse considering the SL’s price and clientele and still didn’t start in first, an irritation Mercedes had already addressed on the sedans. There was also a growing threat from BMW, whose new six-cylinder 2800CS coupe was aimed at the same market as the Mercedes 280SL.
In the summer of 1967, Erich Waxenberger tested at the Nürburgring a W113 test mule into which he’d stuffed the big M100 V8 from the Mercedes 600 and 300SEL 6.3 sedans. The 6,332 cc (386 cu. in.) V8, which had 250 PS (184 kW; 300 bhp SAE gross)) and 370 lb-ft (502 N-m; 435 lb-ft SAE) of torque, made the SL a real hot rod, but jamming the enormous M100 into the W113’s engine bay wasn’t easy and the V8’s substantial extra weight spoiled the roadster’s handling. The project was subsequently abandoned and the test mule scrapped.
The following year, Daimler-Benz engineers explored a more radical idea, creating several W113 prototypes powered by the M50F, a three-rotor Wankel rotary engine with 203 PS (149 kW). Since the W113 was nearing the end of its production life, there was little chance of a rotary W113 being offered for sale, but the M50F was seriously considered for the W113’s planned successor, which was designed with provision for the rotary engine.
A V8 W113 would have been possible had Daimler-Benz been so inclined. In the fall of 1969, the S-Class sedans and 280SE coupe and cabriolet had received the new M116 engine, a 3,499 cc (214 cu. in.) SOHC V8 with 200 PS DIN (147 kW; 230 bhp SAE gross) and 211 lb-ft (286 N-m; 231 lb-ft SAE) of torque The M116 was more compact and considerably lighter than the M100 — in fact, the smaller V8 was only a little heavier than the M130 six — so installing it in the W113 to create a “280SL 3.5” would probably not have been a difficult exercise.
Had the “Pagoda” line continued for a few more years, we assume Daimler-Benz would have offered such a car, which might well have been the most desirable W113. However, by the time such a car would have been ready, the W113’s successor, the R107 roadster, was very close to production, rendering the older car redundant.
W113 production ended in March 1971, although the 280SL remained on sale for the rest of the model year — mainly in the U.S., where the new R107 350SL was not introduced until August. Total W113 production was a respectable 48,912 units, including 19,831 230SLs, 5,196 250SLs and 23,885 280SLs. The six-cylinder Jaguar E-type still outsold the Mercedes, but the W113 figures weren’t bad at all considering the Mercedes-Benz cars’ much higher prices. The W113 also outsold the 190SL and 300SL combined and was probably more profitable than either.