A lot of us, me included, love cars but aren’t totally sure what all of the whacky nomenclature means, especially when looking under the hood. Terms like DOHC, SOHC and OHV can sound confusing and downright intimidating to folks who aren’t completely familiar with the mechanical workings of a car. Don’t worry, though. I’m here to help.
We’re going to take this step by step together, and by the end, you’ll know all of the differences between dual overhead camshafts, single overhead camshafts and overhead valve engines. Then, you can spread your newfound knowledge to everyone else who is too scared to ask someone at a car show for fear of being made fun of.
OHV: Overhead valve
This is a category that is pretty rapidly going away. You’ll be hard-pressed to find an overhead valve — also known as a pushrod — engine in anything outside of a General Motors LS/LT V8 or one of Stellantis’ Hemi V8s. Everything else is a part of our next category, which we’ll get to in a minute.
Pushrod engines are mostly known for putting out heaps of torque at lower engine speeds, but they’re not really able to run at high engine speeds like SOHC or DOHC motors.
Here’s how an overhead valve engine works, according to Cars.com:
[T]he valves, which open and close to let the air-fuel mixture in and out of the cylinders, are above the camshaft, which is in the engine block. The camshaft activates pushrods that move up and down to operate rocker arms that open and close the valves in the cylinder head.
SOHC: Single overhead camshaft
For the most part, a single overhead cam motor is a much more modern setup than its OHV counterpart. Of course, because there are DOHC motors, which are more complex and efficient, single overhead cam motors are usually found in cheaper economy cars. For the most part, they’ve got two valves per cylinder — one intake and one exhaust. There’s nothing wrong with them, though, and they still produce a lot more horsepower for their size and get better fuel economy than OHV engines. The one downside is that they usually don’t produce as much torque.
Here’s how a SOHC motor works, according to Cars.com:
In an OHC engine, the camshaft is in the cylinder head, above the valves, and the camshaft acts directly on the valves or on rocker arms that open and close the valves. On a single OHC engine, one camshaft opens and closes both the intake and exhaust valves.
SOHC engines generally can run at higher speeds than OHV engines[.]
DOHC: Dual overhead camshaft
If you’re driving a modern car, chances are you’re driving something with a dual overhead cam engine. They’re the most efficient type you can get, and they produce the most power for their size. Also known as twin-cam engines, they mostly have four valves per cylinder. Having all of this extra componentry means the engines can operate with better air-fuel mixtures. They can also independently change the timing between each camshaft and the crankshaft. In the biz, we call that variable value timing. It’s some pretty neat stuff if you ask me.
Here’s how a dual overhead cam engine works, according to Cars.com:
With dual camshafts, one operates the intake valves and the other the exhaust valves. On a V-type, or horizontally opposed engine, each cylinder bank will have two camshafts, so there’s four total.
DOHC designs also allow using four valves per cylinder instead of two, which improves air flow and increases power and efficiency. A downside of DOHC engines is that they have more parts and are more expensive to manufacture.
