I have a 300 SDL. They can take a lot of abuse. Their fuel economy on the highway is excellent for such a behemoth of the time period, as it is competitive with modern cars of similar size(city fuel economy isn't all that great).
When I put some Goodyear Assurance Fuel Max tires on mine, I was getting roughly 31 mpg @ 70 mph. Before the LRR tires, it got 30 mpg @ 70 mph. When the turbo failed, it dropped to 28 mpg @ 70 mph.
With regard to the W126 Auto 2000 concept mentioned earlier in this topic:
https://www.motor1.com/news/137525/c...des-auto-2000/
Quote:
Not only did its design preview what was to come in the following years, but the low-slung body was also aerodynamically optimized as the concept had a drag coefficient of just 0.28.
To meet the fuel economy goal, the Auto 2000 concept needed more than just a sleek body. That’s why Mercedes’ engineers came up with three frugal powertrain solutions. The first one was a V8 3.8-liter gasoline engine fitted with cylinder deactivation technology, which as you can imagine was quite the novelty back then. Whenever the engine’s full power was not necessary, half of the cylinders were temporarily shut down to save precious fuel.
The next proposal for an economical engine was a six-cylinder 3.3-liter diesel that had two turbochargers. It granted the Auto 2000 with an “exemplary accelerating power” and needed only 7.5 liters / 100 km (31.3 mpg) while the car was doing 75 mph (120 kph) based on Mercedes’ testing procedures.
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The stock drag coefficient for a 300 SDL is 0.36.
This should give you an overall idea of what is possible, if you decide to go with twin turbos. You may need to upgrade the injector pump with larger threads as well otherwise the engine will never see more than 175 horsepower.
This being said, it is possible to turn the 300 SDL into a 300+ horsepower luxury cruiser that gets 31 mpg at 75 mph. Running this on biofuels would be interesting.