Random idea that I had earlier today. What if there was a Dual Overhead Valve (DOHV) engine? Basically, it would have two pushrods on each side of the cylinder - just like how DOHC is a variation of DAOHC. A DOHV engine could have better breathing with multiple valves and better sparkplug positioning, while still being lighter and more compact than an overhead camshaft. Might make sense for an engine which needs good efficiency but doesn’t need to rev as high. Also could be useful for boxer engines where the space above the cylinders is at a premium.
Still probably a stupid idea, but something interesting to think about!
I can’t say for sure but here is what I think:
It is an idea that sounds good until you think about a few things. All those rods would get in the way of other things such as intake and exhaust ports, spark plugs, and injectors. With only 2 rods per cylinder, there is room left for all that other stuff. That is part of the reason that the camshafts were moved up and the rods did away with.
I always wondered why all valves were round, wouldn’t they be able to breathe better as half moons or ovals?
I was looking into that recently, seemingly it is because the valves rotate in operation and it works out better to just let them rotate as circles than try to hold them in place.
I have never looked too much at diesel engines, that valve setup is something that I have thought of, but my concern was with uneven distribution of opening force, especially at higher RPM. So I guess the float problem is pretty much the same thing.
Another idea I had was channel cam lobes. Where instead of a spring being used to close the valve directly, the spring was used to tension the valve as the valve rode around a channel in the cam. It would make the cam a little heavier to do that, but it would allow for the valve to be fixed so that other shapes could be used.
Isn’t the inherent advantage of overhead valves is that the valvetrain is light, simple and within the block? Wouldn’t having two of them kinda negate the benefits? Besides solid lifter pushrods can rev pretty high anyway.
Ooh ooh ooh! I know! Use OHC on one side and pushrods on the other! Problem solved!
But seriously, injectors and spark plugs can be placed overhead:
And the intake/exhaust ports can be placed on the same side as the pushrods:
@maffc exactly my thoughts! Diesel engines would make the most advantage of the multivalve setup, while minimizing the disadvantages of pushrods. You could also get better combustion and reliability with two cams.
@Deskyx Certainly it wouldn’t be as light as a SOHV, but wouldn’t it be lighter and smaller than DOHC?
In certain configurations, yes. Dual OHV would be lighter in V-engines or Flat-engines than DOHC, but probably weigh as much or more as DOHC in an inline configuration. At least, that’s my thought.
exhibit B Wiki GM
In 2005, the Generation III was superseded by the Generation IV. This category of engines has provisions for high-displacement ranges up to 7,011 cc (7.011 L; 427.8 cu in) and power output to 638 bhp (476 kW). Based on the Generation III design, Generation IV was designed with displacement on demand in mind, a technology that allows every other cylinder in the firing order to be deactivated. It can also accommodate variable valve timing.
A 3-valve per cylinder design was originally slated for the LS7, which would have been a first for a GM pushrod engine; but the idea was shelved owing to design complexities and when the same two-valve configuration as the other Generation III and IV engines proved to be sufficient to meet the goals for the LS7.
The Truck Division instigated a pushrod operated four valve per cylinder, cylinder head conversion in the early 1990s as a means of modernizing/improving and furthering the service life of the Windsor engine. This work was done for Ford by Roush Industries (for 1 million dollars) and two 302ci/5.0L and one 351ci/5.8L variants were built and tested. These engines were highly successful but upper management refused to allow engines so equipped to go into production stating that it was no longer acceptable to use a cast iron block in a new car – one of the 5.0L engines is out there in a hot rod.
and then there is this which can be taken with a grain of salt
