DOHC vs SOHC

[ebbfolls]

Both DOHC and SOHC should be the same, all things being equal (same # of valves, same valve actuation, displacement, etc.).

Theoretically, DOHC's should have an inertial disadvantage by reason of the greater moment of inertia resulting from 2 instead of one camshaft/gear. But the difference is very slight because the crankshaft has a 2:1 mechanical advantage over the camshaft. However, since combustion is so much better with a centrally located spark plug (consider Dodge/Chrysler's "Hemi" design), a DOHC will usually be used for engines designed more for Horsepower than Torque. Another reason is with DOHC, there no longer is a need for tappets as the valves are directly acted upon by the cams. Less moving parts, less inertia and inertial loads, the higher the rpm capacity of the engine, the greater the power output. Thus, more powerful engines are usually found with DOHC rather than SOHC, but that's not to say a DOHC setup is more superior to the SOHC design.

There's more to an engine's power characteristics than the valve train, though that may be a crucial part.