Another subject that I appreciate in the automobile industry more than others is the overhead valve (OHV for short) V8. I specify on the V8 mostly due to how I am not familiar with any recent OHV engines that are not a V8, sans the straight six Cummins turbo-diesel. I do fancy the OHV setup for a few reasons that I find as ways to keep them competitive with their dual overhead cam and single overhead cam rivals.
But here’s a quick recap on a valve train: There are three primary strategies to rotating a camshaft, which opens and closes the valves in an internal combustion engine. We’ll use a V8 as the general architecture. The first, and likely the oldest of the three, is the overhead valve, which uses a single camshaft placed in the middle of the V of a V8. From there, the camshaft shifts pushrods up and down thus opening and closing a valve on top of the cylinder head.
The second, the single overhead cam (SOHC), is utilizing one camshaft per cylinder head. The SOHC powers one head instead of both like the OHV. It thus rocks the, well, the rocker arms back and forth for the intake and exhaust intervals, respectively. This, theoretically, gives more control of the valve lift and engine efficiency.
The third is the dual overhead cam (DOHC). This is the most technical setup that is used on just about all modern V8s, save for FCA and GM, maybe a few others. This system has two camshafts over a cylinder head. One for the intake and the other for the exhaust. This gives the most control of valve timing and can use over four valves per cylinder, one being the 5 valve VW 1.8 engine. This is becoming the most common V8 design, and understandably so.
However, I hold my relatively humble opinion of why I like the OHV even more than the others. The OHV is definitely the most simple, dare I say crude. It has one camshaft and, generally (there are some weird ones out there), only two valves. This combination of one and two don’t make a good engine, in theory.
But the OHV V8 has gained momentum that the SOHC and DOHC can’t, simply by inherent design. The configuration is the cheapest, the most simple for the sake of maintenance and longevity, and the most efficient. That last part though. Efficient? Yes, since it only requires one camshaft, there is not as much power loss as the others in this application. Instead of the V8 pulling two or four moving parts, the camshafts, there is less strain on the crankshaft. OHV V8s also use the otherwise empty space between the V in the engine as the home of the camshaft. This frees up space for the rest of the car’s hood, for the betterment of a lower center of gravity and better engine bay packaging. Not to mention, and I obtained this from Carlos Lago of Edmunds, a supercharger can be added without battling the fitting process of camshafts atop the engine as well.
Now there are a few problems with the two valve setup that an OHV has to deal with, and that is airflow. When people modify GM LS V8s, one of the first things they do is open up the exhaust. Reason being, two larger valves will not, unfortunately, provide as much airflow as four tinier valves, thus making top end power a weakness compared to a four valve. An example is the 6.2 LT1 V8 and the 5.0 Coyote V8. While the LT1 provides more torque, the Coyote will have a top end advantage of the rev range.
The good news is, it has been counteracted. More displacement. The General Motors OHV V8 has always been criticized for having larger engine displacement than the Ford engines because of how they make marginally more power in their respective cars. However, the Coyote is just as heavy and even bigger on the outside.
The photo engine on the left is the 6.2 and the one on the right is the 5.0. As was discussed earlier, the smaller the engine, the better it tends to be for packaging and, in this case, simplicity. This actually becomes a justifiable case for upsizing and engine for competitiveness, which has made me understand that a smaller and lighter overall engine is what truly matters, no matter what is going on in the inside.
Of course I am not saying the SOHC and DOHC engines are bad at all. For me to say that a Fiat 500 Abarth Fire TurboJet turbo four cylinder or an AMG M178 twin turbo eight cylinder is dowdy and overwrought, is complete madness and ignorance on my part. They do their part pristinely like many others in their respective marques.
They are one of those old designs that have made their way into 21st century full steam ahead. Through modern technologies such as direct injection and variable valve timing. And from the looks of them, they are here to stay as long as the V8 itself is.
I hope this helped make a case for an overhead valve engine, particularly in the V8. Also, and apology for not all of the photos being a V8 design. Just a general idea of what they look like.
Thank you