I have a transmission question. It seems that in 1972 the 350SL had a 3 speed automatic transmission. In 1989 the engine and transmission changed, and the transmission was a 4 speed automatic. Both engines have nearly the same torque and horse power. The 0-60 and 1/4 mile times favor the 560SL. This makes me think the extra gear kept the engine in a better area of the torque curve.

Question: Is the 580SL transmission bell housing able to fit a 350SL?? Is the 560 and the 350 engine the same block and bolt patern???

 

The peak horsepower of the 3.5L and 5.6L engines are the same, but at lower RPMs the 5.6 makes much more horsepower and torque. This mostly accounts for the difference in performance. I would guess that a 4-speed tranny could substitute for the 3-speed, but I don't know for a fact.