Bob Sirna has been racing his authentic 1955 Mercedes SL300 at Bonneville since 2001. Petrolicious produced an amazing video (embedded below) of Bob and the car at Bonneville in 2013.
In the quest to always go faster, Bob approached Roush Engines late last year to build a new engine. The goal was to get north of 400 horsepower out of a 3.0 L Mercedes inline-six to have a chance at the current class record of 173 mph. I had difficulty finding exactly what engine model it is but I believe it is a M104 model. The engine ended up making 427 horsepower or 142.3 hp/L. To test they had build not only a powerful engine but also a dependable one, Roush set the engine at 9,500 rpm on the dyno and left it there for nearly one minute.
You can view a few more photos of Bob testing the car in this Ohio Mile photo gallery by Bangshift.