In 1977, a diesel version of the then five-year-old W116 S-Class, the 110mph 300SD, was announced in Frankfurt.
It was earmarked for export only to North America, complete with impact bumpers and quad circular headlights.
The magic ingredient was a turbocharger, making the 300SD the world’s first turbodiesel production vehicle when build began in April 1978.
The five-cylinder OM617.950 unit had an unmistakable diesel clatter about it at tickover, despite attempts to silence it with additional underbonnet sound-deadening, and was strengthened with sodium-filled valves, a tougher crank and a bigger, chain-driven oil pump.
The aim was to build a car with performance equal to a petrol 280S: with 110bhp at 4200rpm, 168Ib ft of torque and a 5000rpm redline, the diesel S-Class could get to 60mph in 12.7 secs with the 450SE’s higher 3.07 rear axle ratio.
Despite a 400Ib weight penalty it was 2.6 secs faster to 55mph than the W123 300D, and posted slightly better consumption figures than the smaller car: 25mpg in the city, 30mpg on the highway.
Inside, there was a 120mph speedo (in some states it only read to 85mph), an idle-speed adjustment knob on the dash and a glow-plug warning light.
The 300SD was the world’s first turbodiesel production vehicle
The 300SD came only as an automatic and had an aluminium bonnet, bootlid and engine firewall to help keep it within the 4000lb weight class.
It was as much a response to new Federal legislation as it was to public demand.
In the wake of the 1973-’74 oil crisis, the US Congress had enacted the Corporate Average Fuel Economy (CAFE for short) standards in 1975, coming into effect in 1978.
This was measured as an average across the full range of models that each manufacturer sold on the American market.
The corporate average to be achieved in 1978 was set at 18mpg, but was due to rise incrementally to 27.5 by 1984.
Those who failed to meet these standards had to pay a fine of $5 per 10th of a mile per gallon over target, plus an additional ‘gas guzzler’ tax.
Priced at $25,000 on its launch, the enthusiastically received 300SD was not intended to be a poverty model: leather, a powered roof and climate control could boost the price considerably.
With 28,634 sold through to 1980, the model was enough of a hit to encourage its maker to build an S-Class diesel on the W126 platform, too.
The last-ever W116 produced in 1980 was an SD, a silver car now on display in the factory museum.
- Sold/number built 1972-’80/473,035
- Construction steel unitary
- Engine iron-block, alloy-head, dohc 2746cc ’six’ with twin Solex carbs or Bosch fuel injection; or iron-block, alloy-heads, sohc-per-bank 3499/4520/6834cc V8, with Bosch fuel injection
- Max power 158bhp @ 5500rpm to 286bhp @ 4250rpm
- Max torque 166lb ft @ 4000rpm to 405lb ft @ 3000rpm
- Transmission four-speed manual or three/four-speed automatic, RWD
- Suspension independent, at front by double wishbones rear semi-trailing arms; coil springs, telescopic dampers, anti-roll bar f/r (6.9 self-levelling hydropneumatic spring/damper units)
- Steering power-assisted recirculating ball
- Brakes vented front, solid rear discs, with servo and optional Bosch ABS post-’78
- Length 16ft 5½-9½in (4960-5118mm)
- Width 6ft 1½in (1867mm)
- Height 4ft 7½in (1410mm)
- Wheelbase 9ft 5-9in (2865-2972mm)
- Weight 3459-4060lb (1610-1842kg)
- 0-60mph 11.5-7.2 secs
- Top speed 118-145mph
- Mpg 13-25
- Price new £6995 (350SE)
- Price now £10-45,000*
*Price correct at date of original publication
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