Hey Scotty,
With all of the V8 engines made by Ford, GM, Chrysler, Toyota, etc., which is a better design: an overhead valve (OHV) or an overhead cam (OHC)? What difference does it make in the end?
For longevity simpler is usually better so you want the overheard valve (OHV) design - which is also known as a pushrod engine and has been around for a long time. You only have one set of camshaft and crankshaft - fewer working parts and easier to work on.
A great example is the GM small block LS-series engine which is highly sought after for engine swaps. These engines had NO variable valve timing, NO direct injection (it was port injection only), NO cylinder deactivation - although these technologies are not unique to any particular engine architecture.
I like the old flathead engines. Simple to work on.
Why did flatheads fall out of favor from auto makers?
Although simple to build and service the combustion chamber shape and valve locations are wrong for best power and efficiency. In the case of the engine in the photo (early 1960s Rambler American) the flathead engine put out 90 hp. The OHV adaptation of the same engine put out 127 hp.
For V8 engines when the valves are both on the same side of the combustion chamber ("L-head"), which is the most common design so the valves can work off a common camshaft, either you wind up with very complex and expensive plumbing for intake and exhaust or you have a design like the Ford flathead V8 where exhaust is routed through the block to the other side of the engine, leading to overheating problems.
I believe a lawn mower is about the only place that you'll see a new flathead engine nowadays. Head gaskets are easy to do, the head just bolts on and off. I'm somewhat surprised California hasn't applied gasoline car standards for emissions to lawn mowers. Haha. They ruined gas cans with their emissions consciousness.
Interesting Chuck and Justin. Thanks!
As Kester Paul says, the difference in the two is where the camshaft is/ are, and how many there are. The difference is primarily weight, efficiency and the corresponding performance changes. The Overhead Cam design has lobes on the cams that directly press down on hydraulic valve lifters, deleting the pushrods, valve return springs and rocker arms from the Overhead Valve design, saving considerable weight. The saved weight means the engine can rev much higher before catastrophic failure. The phenomenon of "valve float" is also much reduced. The disadvantage is less durability and longevity. Hydraulic lifters will wear before a steel spring, as the spring won't "break" unless it is pushed past its fatigue strength. A hydraulic lifter will eventually leak or become weak as it wears. This is generally the cause of the valve ticking sound when an OHC engine's valvetrain starts wearing out, but not always.
The overhead cam design also allows you to put more than one camshaft over each cylinder head, instead of just one. In a SOHC (single overhead cam) you create two cams instead of one centralized one on the Overhead Valve design. This simplifies the cam design, since it's only operating valves on 3 or 4 cylinders, not all six or eight at once. For a Dual Overhead Cam design (DOHC) there are two cams over each cylinder head, one providing control over the timing on the intake cycle of the engine, and the other manipulating the timing of the exhaust cycle. This design provides the most control to the variable valve timing system and allows the computer to really extract as much power as possible from the gasoline. The disadvantage of the DOHC engine is the engine is quite wide up top, relative to a similar displacement OHV or SOHC engine. As an example, this is why Ford could not keep the original Ranger design and stick more modern V6s in it than the pushrod 3.0 Vulcan V6 from the 1980s, or the 4.0 SOHC Cologne V6. The engine bay is not wide enough.
As far as lubrication, the overhead cam designs require more motor oil, since there are two or more cams, not one. The OHC designs will wear faster on start-up than the OHV design, because the OHC doesn't get oil pumped to it as rapidly, being that they are at the very top of the engine. In the OHV engine, the cam is in the center of the "V", putting it closer to the oil pump.
Just realized @DayWalker provided the answer I was referencing, and Kester Paul asked the question. Haha.