A pushrod engine, also colloquially referred to as an overhead valve engine, is a design that has been in many cars for decades. General Motors and Chrysler have used this type of engine in several of their models. Many people may refer to them as “archaic” and “obsolete,” especially given alternative designs for engines that have been created since the pushrod engine was designed, such as the straight-six engine.

However, the pushrod engine has stayed a mainstay of engine designs throughout the years. A large part of its longevity lies in its practicality. Several reasons have been noted as to why the design works so well, pointing out the benefits of a pushrod engine's interior physiology and how it benefits the vehicle it's in.

That said, there are also a few drawbacks of a pushrod engine that, while easily resolved or countered, present obstacles that should be taken into consideration. Read on to find more about the inner workings of a pushrod engine, as well as its benefits and detriments.

Related: Ford's Newest Crate Engine: The 430-HP 7.3-Liter Pushrod "Godzilla" V8

How Pushrod Engines Actually Work

1928 BSA Motorcycle pushrod single cylinder engine close-up view
Via: Wikimedia Commons

The term “pushrod engine” may be unfamiliar or be acknowledged under other names. For example, they are also sometimes referred to as an “Overhead Valve Engine.” These engines are often seen in American automakers and have advantages that guarantee their continued relevancy.

These engines succeeded the flathead engines, which were known for having valves that were located in the engine block alongside the cylinder. While flathead engines were both inexpensive and compact, their poor airflow and combustion demonstrated their inefficiency and lack of power.

Compare that with the pushrod engine, where long pushrods protrude up from the valley and extend up from the camshaft to above the top of the cylinder. At that point, the pushrods make contact with rocker arms, which press the inverted valve away from the head casting, actuating valves atop the cylinder heads.

These engines rose to prominence soon following the conclusion of World War II, when Lincoln and Cadillac debuted them in their vehicles. When the famed Chevy V8 (one of the best V8 engines out there still) debuted in 1955, the pushrod V8 became much more commonplace. Further, increasing the use of the pushrod engine was Chrysler's famed Hemi V8, released around the same time.

Pushrod Engines Pack Persisting With Practicality

Pushrod Engine, Dodge Challenger SRT Hellcat Redeye
Via: Dodge

The practicality of these engines has allowed them to persist throughout the years. GM continues to use these engines in the latest iterations of its small-block V8 engine, and Volkswagen continues to use these engines well into 2022. Even though pushrod engines are often considered to be 'older designs,' many aspects have shown themselves to be beneficial or practical in some fashion.

For example, a pushrod engine is more compact than an overhead cam design. The latter has a bulkier engine design thanks to stacking both camshafts and the cam drive system atop the cylinder head. The bulkier design also means more weight and increased mass, which raises the center of gravity on the engine as a whole.

These engines necessitate increased machine work thanks to increased mass, which also makes them more expensive to construct and repair. With pushrod engines, the initial design lacks bulk and weight, avoiding the domino effect of further problems and resulting in cheaper construction and repair. Their simplicity is seen as appealing when it comes to maintenance or making modifications.

The design is also simpler, and because it lacks miscellaneous parts, there are altogether fewer variables to potentially cause problems. Remember how overhead cam engines are bulkier and heavier, and their increased number of parts compared to pushrod engines adds to their weight. The lack of parts in pushrod engines means lighter weight.

Another aspect of note is pushrod engines tend to require less fuel than overhead cam engines because the latter has characteristically higher engine speeds, which necessitates extra fuel to operate. Also of note is the pushrod design also offers an engineering advantage at lower RPMs: its more efficient airflow helps make power early and falls flat higher up. An overhead cam engine has to have the driver rev up the engine to generate more power.

Related: Check Out Ford's All-New 7.3 Liter "Godzilla" Pushrod V-8 Dyno'ed

Pushrods Are Their Own Worst Enemy

A Clerget 9 aviation engine with pushrods
Via: Wikimedia Commons

Ironically, the pushrods themselves are one of the biggest drawbacks of their engines. Pushrods and the rocker arms that often accompany them have limitations, with the main one being the mass of these parts limits revolutions.

When the vehicle hits higher speeds, inertia keeps valves from closing before the camshaft opens the valves again. To counter this, one or two camshafts need to be placed on the cylinder head. This will act on valves without the pushrods and inertia.

Further, as noted before, while the pushrod engine gets power early, by the same token, it fails to rev as high as a comparable overhead-cam engine. Also, a unique aspect of the pushrod engine is that the camshaft is located inside the cylinder block, as opposed to on top of the cylinder head, which decreases overall engine height.

Because of the lower height, the camshaft rotation travels through both a pushrod and a rocker-arm. The rocker-arm pushes down on a spring to open the valves, and more reciprocating mass is generated as a result.

Further, Disadvantages Of Pushrod Engines

Pushrod Engine, Dodge Durango SRT Hellcat
Via: Dodge

While minor and manageable, pushrod engines have a few other detriments that come into play. Pushrod engines have the added step of incorporating tall and skinny intake ports with protuberances, and the design only lends itself to two valves per cylinder.

Additional valves would overcomplicate the design. Friction and wear are increased because large valves and greater valvetrain mass combined require heavy springs. While the disadvantages don't exceed the advantages, it is important to note these drawbacks and plan accordingly when dealing with a pushrod engine.

Sources: Designnews, Advanceautoparts, General Motors, Engineering Explained Via YouTube