Topic: Why did DOHC take over?

[croquesaveur]

I notice that all modern engines seem to be DOHC.  I can't, off the top of my head think of any advantages of this design over SOHC, but I can think of disadvantages (more complicated, more parts, more weight).

Can anyone tell me why DOHC won?

[Big Jay]

Because you can time the intake and exhaust cams separately. Also you can get rid of the heavy rocker arms for increased RPM.

Jay

[puppytrax]

You can position the valves for a more advantageous combustion chamber shape...and decreased valvetrain weight, which equals higher revs without valve float...

[croquesaveur]

1) Separate intake/exhaust valve timing.  Couldn't this be accomplished with separate cam lobes on a SOHC?
2) Better combustion chamber shape.  Couldn't clever rocker arm design overcome this?
3) Less weight.  How can two cams and two timing chains and two sets of timing sprockets and all the additional engine case metal to cover it all weigh less?

Thanks for the rapid response guys!

[Manny]

I think it's also so that each cylinder can have more valves - more volume in/out per time valve is open. Please correct me if I'm wrong.

[Roach Carver]

I think it was a plot by camshaft maunfacturers

[cb650]

Yes two smaller lighter valves will allow more volume. Yami has a 5 valve and seems there was some thing that went six.




                Terry

 

 

 

[Bodi]

The main advantage is reduced moving mass in the valvetrain. The rocker is eliminated and the cam operates the valve more or less directly through a clearance adjusting bucket and shim.
The reduced mass allows a smaller valvespring or higher RPM or more lift or more aggressive acceleration curves - or some combination of these.
Mostly it was (and is) a marketing exercise, the Z1 came with DOHC on its feature list and Honda had to play along. Now even Hardley has a twin cam - pushrod - engine...

[Pinhead]

Twin cam pushrod engine???  Doh!

[oldbiker]

Twin cam push rod. otherwise known as a traction engine.

[puppytrax]

Twin cam pushrod engine???  Doh!

Penske had a twin cam Mercedes pushrod V8 engine in Indycars not all that long ago...both cams in the block, and pushrods only 1 1/2" long...it was outlawed after only one season (maybe only one race, I can't recall now)...It kept winning...(Indycars were allowed larger displacement for pushrod engines)...

And if you didn't know, the [older] Triumph vertical twins used two cams, in the engine block...