Direct Acting Overhead Cam vs. Pushrods and SOHC/DOHC

I’ve been trying to find information on direct acting overhead cam engines, but ironically some of the top results are actually for threads on this forum. I’m wondering about the historical and/or contemporary applications of the technology for engines, as well as how it compares to pushrod and SOHC/DOHC designs. Is it more closely related to one or the other, and can engines designed for pushrods be easily produced with direct acting cam head variants? What about SOHC/DOHC designs? Also, what kind of advantages and disadvantages do they have relative to the other engine types, and what real life examples are there?–dohc.html

this image shows a DAOHC a SOHC and and pushrod. as you can see both DAOHC and pushrod valves are in the center of the cylinder where as SOHC are angled.

the sohc and the pushrod are both using rocker arms to activate the valves. where as the DAOHC is using the same activation method as a DOHC set up, at least in game.

as far as the game is concerned imagine a DAOHC as half of a DOHC setup there are a lot of different real world setups but lets just stick to in game.

Pushrod is the cheapest, and lowest revving, it’s advantage is it’s lightweight, minimum space requirement, and durability. it’s drawbacks are limited valve space therefore limited power, and it’s inherent valvetrain weight limits it’s rev range.

SOHC is a setup allowing you to run 2, 3, or 4 valves per cylinder, however the more valves you add the more stress you put on the cam and you lose reliability. It’s cheaper and lighter than a dohc but is not as powerful, efficient or durable, nor can it rev as high on larger bore engines due again to larger valves stressing the camshaft.

DAOHC is a cheaper alternative for high revving engines, with less moving parts then any other setup its the most reliable to rev hard, however it’s valve placement limits valve size and therefore it is not as powerful as a SOHC, nor as efficient, but it’s lighter, cheaper, and more durable then anything aside from a pushrod.

DOHC is the most expensive, heaviest, most efficient, and highest revving of the lot, with options for 2,4, or 5 valves. it is made from two Direct acting camshafts set above valves set at the same angles as in the SOHC, it has all the benefits of the single DAOHC with the added bonus of the SOHC’s valve placement which allows both bigger valves than the DAOHC as well as more valves .

For a better understanding select each setup in game, use the right hand vertical slider bar to expose the valves, and zoom in while it’s running to get a better idea of how it all works.

Also for info on DAOHC look up “Top-hat shims” or “bucket under shim”.

Are direct acting overhead cams mostly used on motorcycle engines? I’ve found quite a few motorcycles that use the technology, but I haven’t found any cars yet.

Now a days yeah, cheap, light, compact, and high revving. I think in the 50’s jaguar and fiat used it as well as a few others, it’s almost totally phased out on single cam engines now though.

I thought Jaguar used two valve SOHC heads on its XK6 series engines? Might some sources use SOHC to describe direct acting overhead cam designs?

Also, I suppose I could have my company start in the 1940s with a small sub-liter four cylinder direct acting overhead cam design and say it was for a motorcycle project. :laughing:

Almost every source will describe it as either just SOHC, or maaaaybe bucket tappet SOHC.

As used in things like older SOHC VW Golf motors - … MhrPoA.jpg

Jaguar V12 - … G_0421.jpg

And sort of (but with follower thingys) Nissan L series -

As compared to a traditional rocker based SOHC design - … _D15A3.JPG

Don’t forget the Volvo B23/B230 family of 8 valve engines.
And the aftermarket 8 valve Evo heads for Volvo B23.

The very common fiat 128 engine is DAOHC … _cutup.jpg