It’s time go inside the internal combustion engine and take a closer look at the all-important valvetrain. This is the assembly that regulates the fuel-air mixture’s flow into the combustion chamber (intake), seals it shut to build compression for the power stroke, and finally removes the gases afterward (exhaust). An engine, in its essence, is actually just a big air pump and this system controls how and when the air moves.
In a four-stroke, gasoline-powered engine, this is a delicate dance that is highly choreographed, and any misalignment is magnified. Valvetrains come in many different configurations ranging from the early side-valve engines (aka “flatheads”) to highly complex pneumatic systems that became all the rage in 1980s F1 cars.
By the end of this article, you’ll know your pushrods from your desmodromic valves (where the Ducati Desmosedici gets its name), as we explore the innovations and innovators that got us to where we are today.
Let’s take a quick moment to orient ourselves to the main subcomponents that make up the valvetrain. They are as follows:
Valves — They have one and only one function: to seal. They need to create a tight closure of the aperture so that the gases stay inside to build pressure for the combustion and power strokes, as well as not allow gases to go in the wrong direction. There can be as few as two valves per cylinder and up to five. (Okay, some do have a secondary function, that being the creation of vortices in the chamber to evenly distribute the fuel-air mixture, but that’s a topic for longer discussion.)
Camshafts (Opening Mechanism) — Almost 100 percent of the time this is a camshaft. A series of cam lobes converts rotating motion into up/down motion by mechanically pushing a rod or stem away from the center of the rotating shaft. The lobe contacts a pushrod/rocker arm system via a tappet or the valve stem.
Camshafts can be positioned low in the engine (camshaft in block) or above the combustion chamber (overhead). The shape of the lobe dictates how far the valve opens and for how long. In some rare instances, valves can be opened pneumatically, hydraulically, or with a direct gear.
Valve Spring (Closing Mechanism) — Again, almost 100 percent of the time this a valve spring. It is compressed when the valve opens. When that force is removed, the spring almost instantaneously closes it up for a tight seal. That valve spring has been a common point of failure, but better metallurgical research has made it much less so. In racing engines, alternative technologies are used since a mechanical spring cannot keep pace when running at 10,000 rpm!
Valve Position — While not a component, per se, another defining characteristic is where the valve is positioned in relation to the cylinder. The vast majority are on top, but earlier engines had the valves not in the cylinder itself, but in a side chamber where, in some designs, the actual combustion also took place.
The early automobiles were focused mostly on function and less so on performance. Thus the first cars used a side valve configuration and are referred to as “flatheads” because the combustion chamber was not located above the piston, but rather off to the side.
The earliest versions had the intake and exhaust valves adjacent to each other on one side, called an “L head.” Then a crossflow head was introduced that had them on opposite sides (“T head”). The transformational Ford Models T and A used an inline 4-cylinder engine that had an L-head configuration.
Side-valve engines have just a few parts. Thus, they are simple and reliable. What they aren’t is performant. The gases don’t move efficiently, don’t burn well, and have low compression. When these became considerations, a better way emerged that put the combustion chamber directly above the cylinder.
The first car known to use overhead valves was the 1902 Maudslay in England, with a similar design appearing in 1903 from Illinois-based Marr Auto Car. The first production car with a single-overhead camshaft was the Isotta-Fraschini Tipo KM in 1910.
The big breakthrough was the 1912 Peugeot Grand Prix car which had the “L76” engine, the first to have a dual-overhead camshaft (DOHC), four valves per cylinder, and hemispherical combustion chambers. Developed by Jules Goux and Ernest Henry, they realized that the key to more power was a higher revving engine with much greater airflow. This early Peugeot become the template for the modern engines that we use to this day.
Peugeot proved the design on the race track, winning both the 1912 and 1913 French Grand Prix with this radical new innovation. Mercedes followed suit with the 18/100 GP which won the 1914 edition of the French race. The first road cars with DOHC were the 1926 Sunbeam Super Sport followed by the Duesenberg Model J in 1928.
Mercedes-Benz experimented (successfully) with an alternative way to open and close the valves in their world-beating W196 Grand Prix cars and 300SLR sports cars from the mid-50s. They used a desmodromic drive which mechanically opened and closed the valve, thus eliminating the need for valve springs. The camshaft rotated a rocker lever attached to a valve stem that positively opened and closed a valve directly. In theory, it would add reliability but those problems got solved in other ways and the desmodromic valves introduced other complexities. They are still present today, by Ducati which uses this in their Desmosedici (Italian for "desmodromic sixteen") engines that drive their MotoGP bikes.
The shift to more efficient, multivalve configurations was well accepted in motorsport, but took much longer to be commercialized for road car use. In addition to the aforementioned Peugeot, A.L.F.A., Bugatti, Stutz, Pierce-Arrow, Bentley, Mercedes, and Duesenberg were using three, four, and even five-valve configurations in their race cars way back in the 1920s. A few production models were indeed made available to the public, but they were limited runs used primarily on “sport” editions. After WWII, it seems the multivalve concept got lost.
Cosworth Engineering revived the multivalve concept in 1966. The company first developed the Cosworth FVA engine, an inline 4-cylinder with four valves per cylinder, as a prototype for an upcoming V8 version. The 3.0L V8 DFV (for “Double Four Valve”) was released in 1967 and transformed Formula One. The DFV become the most dominant engine in Formula One history with 167 wins — and renewed interest in four-valve engines.
In 1968, Toyota ran a four-valve 5.0L engine at the Japanese Grand Prix, which signaled that the Japanese automakers were in the multivalve-engine game. In fact, Nissan was quick to market with the S20 engine, a 2.0L inline six-cylinder engine with DOHC and four-valves per cylinder. The S20 powered the 1969 Nissan Skyline and the Fairlady racing edition.
Next up was a Ford Escort RS1600 with a Cosworth-designed four-cylinder that was available in 1970. This model became a huge hit and dominated domestic and international rally competitions in its era. By the end of the 1970s, Chevrolet, Fiat, Lotus, BMW, and Porsche had production models available that targeted the sports and performance segments. The “quattrovalvole” got the exotic car treatment in the 1980s with the 1982 Ferrari 308. Then, it appeared inV12s powering both the 1984 Ferrari Testarossa and 1985 Lamborghini Countach QV.
Watch this screaming Renault RVS-9 V10 F1 engine rev to 20,000 RPM!
With the performance advantages that could be gained from an optimized valvetrain, the drive for more gains — both marginal and otherwise — was on. The engineers of the time were working to use different materials and tricky methodologies to improve volumetric performance, fuel efficiency, and keep up with the demands of motorsports.
In the early 80s, Renault developed the pneumatic valve spring and featured it in their RVS-9 1.5L V10 turbocharged engine. Renault’s Jean-Pierre Boudy is credited with the invention which updated the hydraulic valve lifter, first utilized in 1930, and became ubiquitous by the 1980s.
As engine RPMs were climbing above 10,000 RPM, it was pushing the ability of a mechanical spring to return the valve quickly beyond its limits. At 12,000 RPM, a spring is asked to return the valve 50 times every second! The idea was to replace the mechanical valve spring with a sealed chamber filled with an inert gas like nitrogen, maintaining the contact force without suffering from fatigue failure. Pneumatic valve springs have been the standard in F1 ever since.
Engine designers have also developed techniques for varying both valve lift and timing that allow an engine running at low RPMs to operate efficiently. When the engine is put under load, it can recalibrate the engine to get maximum power by opening the valves wider and at slightly different times. Some inventive designers filed patents around these ideas as early as the turn of the 20th century. This technology was banned by F1 so most development has been focused on road car use.
Fiat’s Giovanni Torazza developed a variable valve timing system using hydraulic pressure in the 1960s. Alfa Romeo was the first-to-market with its own version developed by Giampaolo Garcea in the 1970s. Beginning in 1980, the Alfa Romeo 2000 Spider had a mechanical VVT in it, the first production car known to do so.
The most widely known system of this sort is Honda’s VTEC (Variable Valve Timing and Electronic Control) invented by Ikuo Kajitani. It used two separate cam profiles and could switch between them seamlessly. VTEC first appeared in the 1989 Integra XSi, CRX, and Civic. In 1991, it appeared in the flagship NSX mid-engine supercar which gave VTEC tremendous credibility.
The next evolution being explored is the so-called “camless engine” which operates the valves using electromagnetic, pneumatic, or hydraulic actuators. While nothing is yet in production, the idea is being actively pursued. The most advanced version is coming out of Koenigsegg utilizing their so-called “Freevalve” technology. If successful, this would give unprecedented control over an engine’s performance and efficiency by instantaneously adjusting timing and valve height on demand.
The valvetrain is a critical component that dictates a great deal about an engine’s performance. While it seemingly went dormant from the 1920s to the 1960s, new technologies are now in the offing that could potentially extend a lifeline to the internal combustion engine in both cars and other applications.