The name of this car comes from the size of its engine. At 3 liters, this was a car built for performance but with style as a bonus. The gullwing doors, for instance, were not just to look cool. They were necessary because the 300SL needed a tubular frame. You can see from the picture that getting into this car would be difficult because the entrance is not very low to the ground. This is all part of that tubular design.
This car was one of the first major production cars to have fuel injection. That little feature doubled the horsepower to a robust 240. With the size of this car and all those ponies under the hood, it's no wonder it got down the road quicker than just about anything of its time. It could reach a top speed of 161 miles per hour.
There was a design flaw that can be attributed to the lack of knowledge about fuel injection and the lack of any technology to remedy the situation. Gasoline was continually pumped into the engine after the ignition was turned off and before the engine actually stopped. This happened because the system was mechanical; there wasn't any computer to tell the fuel injection system to stop pumping. This would lead to gasoline in the engine, diluting the oil. It was actually better for drivers to drive the 300SL hard before shutting the car off, so the heat from the engine could burn off the excess gasoline.
These cars are rare and very coveted by the collector car market. These are the cars that define a collection. You won't find them at your local car club, unless you're lucky to have a very rich member. They sometimes get listed on eBay, but bidding can get fierce.