Topic: ELI5: 4 valve per cylinder SOHC vs 4 valve per cylinder DOHC

[erleiniw]

Hello everyone,

on 4 valves/cylinder SOHC, a single lobe on the camshaft pushes 2 valves,

and on DOHC, a single camshaft lobe pushes 1 valve.

on my logic, it seems SOHC is better since there is 1 less moving parts walmartone (1 less camshaft)

but in reality, i see more and more everyday economical cars use 4 valve SOHC

[Kelly E]

DOHC motors have less moving parts because the cam lobe pushes directly on the valves eliminating the followers and adjusters.

[PeWe]

More freedom how to time the cams with Dohc. Adjust the duration and overlap. High compression causing pinging, open it up for more overlap as long as valves runs free from each other and pistons. The other way possible too, decrease overlap , increase compression.

Sohc cam has less tuning possibilities.  You cant change in vs ex relation (overlap) except  just a little by  different valve lash. More lash, less duration and  overlap. Less lift too.

I guess ex can like some extra lash on some cams.

[MRieck]

More freedom how to time the cams with Dohc. Adjust the duration and overlap. High compression causing pinging, open it up for more overlap as long as valves runs free from each other and pistons. The other way possible too, decrease overlap , increase compression.

Sohc cam has less tuning possibilities.  You cant change in vs ex relation (overlap) except  just a little by  different valve lash. More lash, less duration and  overlap. Less lift too.

I guess ex can like some extra lash on some cams.

Also easier reduce the valve angle with 2 cams giving you a smaller, more efficient chamber.

[PeWe]

More freedom how to time the cams with Dohc. Adjust the duration and overlap. High compression causing pinging, open it up for more overlap as long as valves runs free from each other and pistons. The other way possible too, decrease overlap , increase compression.

Sohc cam has less tuning possibilities.  You cant change in vs ex relation (overlap) except  just a little by  different valve lash. More lash, less duration and  overlap. Less lift too.

I guess ex can like some extra lash on some cams.

Also easier reduce the valve angle with 2 cams giving you a smaller, more efficient chamber.

CB750 should have got a head like Kawasaki Z1 900/ 1000 with   larger ports and valves much earlier in the  K0- K8, F era.

A modified Z1 900/1000 can deliver loads of fun raw power!

 The later CB750 Dohc (still lack of power) miss the old nice look CB750 and Kawasaki had in the 70's.