I was riding my bike to school when I heard an extremely loud sound behind me. I turned around and there was a Mercedes-Benz that resembled a 190, and it dashed by me at around 120 mph in a 25 mph zone. It accelerated extremely quickly, sounded like a V10/V12. Might have been a boxer 10. A very unique sound. Any help with car? It had four circular headlights, and it WAS a Mercedes. After identification of the car, I will move on to engine. Thanks!

Update: It was a W123!

Now, the engine. Anybody know about a V10 or V12 in a W123?