Its unassuming looks lulled you into a false sense of security. The grandpa car couldn’t go that fast, could it? Hiding a 6.3-litre V8 under the bonnet, it could. The 300 SEL 6.3 was a soft-riding mile muncher — that just so happened to go like a Lamborghini.

It came along almost by chance. The story goes that in the Sixties Mercedes engineer Erich Waxenberger was fed up of being ribbed by German automotive scribes who believed he was making cars fit for little old ladies. Upset by the criticism, he worked after hours at the Sindelfingen factory to prove them wrong and did so by taking a S-Class and shoving the massive mill from the 600 limousine in the engine bay.

Back then, the S-Class only had six-cylinder engines and mustered up 130 horses. It wasn’t the most potent and had a bit of an old person’s car tag, but Erich changed that notion; the smaller 300 SEL produced a whopping 300 horses and 588Nm of torque. It could hit 100kph in 6.5 seconds, which for a saloon in 1968 — the year the model was launched — was unheard of. Powerful V8 saloons from almost every manufacturer are commonplace today, but back then, this was a novel concept.

It was Merc’s version of the muscle car and it isn’t a surprise that AMG took it racing before any other Benz — but it didn’t forgo any luxury or quality in the name of power; it featured air suspension, ventilated disk brakes in all four corners, a smooth-shifting four-speed automatic transmission, power windows and power steering. It looked no different to a regular 300 SEL, but the discreet 6.3 badge on the right of the boot lid gave it away. It was a huge success in both sales and image-building for the Stuttgart carmaker which, thanks to new models from BMW, had started losing its rep as king of the autobahn.

Production ended in 1972 with just 6,526 units built (the first 100 were hand-made) and the W109 S-Class was replaced by the W116 series. The 6.3s are quite rare today but even if you find one, it won’t break the bank; well-cared-for models have a price tag of roughly Dh250,000.