Let’s face it, the year is 2021 and we, as a whole society overall, are fairly certain of our technical superiority. The engines rolling out of factories today are the most refined and reliable powerplants ever produced by human beings. As it stands today, from the factory, four-valve engines are the most powerful and efficient designs on the market (even though there are a few two-valve designs that like to throw a wrench into that statement). But, what about five-valve engines? Or six valves, or seven valves?
If four valves per cylinder are good, more must be better, right? The answer to that is, “to an extent.” There exists a law of diminishing returns based on current designs and technology, which have seemed to cause the industry to settle on the four-valve arrangement being the peak of all-around efficiency. But, there are several very commercially successful engine designs with more than four valves per cylinder, as well as some unsuccessful ones, which were just as valuable in showing us where the limits were, practical or otherwise.
Here, we’ll briefly discuss five engines with five or more valves per cylinder, both successful and not.
Audi has been a proponent of the five-valve engine for quite a long time. They produced their first five-valve engine in 1988 with the experimental 2.2-liter inline-five-cylinder engine that made 641 horsepower and set several world speed records. It wouldn’t be until 1995 that Audi would produce the five-valve 1.8-liter turbo four-cylinder for public consumption. It can be argued that the Audi 1.8-liter five-valve design was the most commercially successful design, as it powered at least 16 different vehicles.
Now, to present a completely different image of five-valve production engines than something powering Volkswagen’s New Beetle, let’s talk about Ferrari’s five-valve production cylinder heads. Manufactured for a decade (or 11 model-years, if you want to be pedantic), the 3.5-liter and 3.6-liter variants of the Dino V8 from Ferrari were the end of an era. Making 375 horsepower and 395 horsepower for the road variants of the F129 and F131 engines, respectively, the F131 saw 419 horsepower in the 360 Challenge Stradale variant.
It wasn’t just Europeans who jumped onto the five-valve per cylinder bandwagon. Toyota’s famous 4A-GE 1.6-liter inline four-cylinder engine received a Yamaha-designed five-valve cylinder head in its fourth generation, starting in 1991. Like the Ferrari five-valve design, the “Silver Top” and “Black Top” variants of the engine spanned a decade and capped off that engine’s production. Peak production ratings for the five-valve versions were 160 horsepower at 7,800 rpm and 119 lb-ft at 5,600 rpm, with the version used in Formula Atlantic rated at 240 horsepower at 10,000 rpm.
Getting into the “more is better” theme of the 1980s, Maserati decided to develop a six-valve dual overhead camshaft engine with twin-turbochargers that would make a whopping 261 horsepower (remember, this was in the 1980s). With the center valves at different angles than the outer valves, this would, in theory, create more swirl and better efficiency. While it was quite an advance, theoretically, it was ultimately dismissed in favor of a four-valve design, leaving the 4AC as the closest we’ve ever come to a production engine with more than five valves per cylinder.
Yamaha Genesis 7-Valve
While the 7-valve variant of the Genesis engine really wasn’t ever close to production, it is important because it really showed that there is such thing as too much. A leader in multi-valve technology at the time, Yamaha experimented with its Genesis engine program to find out how many valves shoved into a combustion chamber were too many. With four intake valves, three exhaust valves, and two spark plugs per cylinder, the R&D team finally found the wall. In fact, they also tried an experimental six-valve design as well, and found it to perform worse than a five-valve design, setting the standard early on for five-valve-per-cylinder designs.