The differences between OHV, SOHC, and DOHC

Intro

The camshafts are one of the most important components of an engine. It’s what gets the air into the engine, and takes out the dirty exhaust gas. With out them the engine wouldn’t be properly functioning (or at all really) then you wouldn’t be able to go anywhere. So today I’m going to go over the 3 main types of camshaft layout: OHV, or Over Head Valve; DOHC, or Dual Over Head Cam; and SOHC, or Single Over Head Cam. I will go over how they sit on an engine, and some of the pros and cons of each. So without further delays, let’s start with the first one

DOHC

Commonly known as twin cam, quad cam, the DOHC (or Dual Over Head Cam(shafts)) is one of the most common forms of cam setup. It consists of two rods with cam lobes for each bank of cylinders. For example: A RB26 has two camshafts (because it is an inline engine, therefore only needing two), and a F154 has four camshafts (as it is a V8, requiring two for each side)

Pros: More efficient, can make more power as it allows the engine to have 4 valves/cylinder rather than two or three.

Cons: Taller compared to OHV as the cams are on top of the engine, rather than in it, more expensive to make as there are more moving parts

Examples: 2JZ, RB26, EJ25, 4A-GE, VR38DETT, SR20DET

SOHC

Less common than say DOHC and OHV, but it’s not to say it’s worse. Due to only having one camshaft for each bank of cylinders, the Single Over Head Cam is lighter and simpler than it’s twin cam counterpart. And because there are less components, it’s cheaper to make as well. Now in a lot of applications in the past, the SOHC has typically only had 2 valves/cylinder. However, modern day single cams now have 4 valves/cylinder. Cars such as the Fiat 124, Alfa Romeo Guilia, and Honda Pilot.

Pros: Cheaper than DOHC, lighter (weight reduction brooooooo, even though not by much), simple

Cons: The need for a wider cam could increase engineering costs

Examples: Mercedes M275 (6.0L twin turbo V12)

OHV

The most common American V8 setup (and V10, RIP Viper), this simple layout consists of one camshaft in the V of the engine, and pushrods mounted in the V just above the camshaft to hit the rocker arms. In case some of you were wondering, the Chevy LS “small block” gets it’s name from the fact that because it’s an Over Head Valve, therefore not heading a traditional cylinder head, it makes it a lot smaller than a Coyote equivalent (which is DOHC). Whereas OHC engines can use anywhere from 2 valves per cylinder to 5 (in super rare, when all the stars align on a blue moon), an OHV is limited to 2 valves per cylinder as there is no practical way to make any more (or anyway for that matter).

Pros: More compact than a OHC engine

Cons: Can’t rev as high due to danger of breaking the pushrods, slightly more complicated than a OHC engine

Examples: Any Hemi engine, any LS engine, Viper V10

In conclusion

That’ll wrap things up for this brief article showing the basic differences between the three main types of valve train layouts. If there is anything I need to add or change, let me know in the comments (I’m learning this stuff too). Until next time, I will catch up with you guys later. Bye!

P.S. Whoever can figure out what I did with the engines (what I did with the examples) gets a Ferrari

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Comments (24)
  • Alfa Guilias aren't SOHC, they're all twin cams. In fact, I'm pretty sure that every Alfa straight-four for the last fifty-odd years has been a twincam engine.

    1 year ago
  • OHC also will give better fuel efficiency over DOHC

    1 year ago

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