"I was drag racing in a Prius. I don't win a lot." While just about every line from a Hollywood movie ends up as a meme today, in the case of Jason Bateman in 2011's Horrible Bosses, the joke's T-shirt transformation was fully justified.
OK, so we know the Toyota Prius doesn't win races because it's not designed to. More specifically, though, there's a reason they don't - and that's because their engines are designed to optimize efficiency over velocity.
The NC-gen Mazda Miata developed 126 hp from its 1.8-liter engine. In the same period, the third-gen Prius also had an identically-sized engine - but one that could only muster 95 hp. Being a hybrid, it was further boosted by an electric motor to achieve a total output of 138 hp.
The two cars couldn't be any different in philosophy, but what's with that power deficiency? Enter the differences between the Mazda's conventional Otto cycle engine and the Atkinson cycle in the Prius.
While the car that immortalized mass-market adoption of hybrid technology, the Toyota Prius, first saw the light in 1997, the technology employed by its internal combustion engine for ozone-saving application actually predates the Prius by more than a century.
The original four-stroke Otto engine, first devised in Germany during the 1860s, remains the blueprint for how gas-powered engines still operate even today; completing the following stages over two rotations of the crankshaft, to which the pistons are connected.
This is a pretty cool vantage point.
While certainly groundbreaking, the Otto engine wasn't particularly efficient as its parasitic losses equaled, if not exceeded, the power it produced. It wasn't long before a British engineer named James Atkinson devised an enhanced interpretation of the four-stroke Otto engine in 1882. His addition of linkages halved the number of crankshaft rotations, which immediately increased energy efficiency. Yet its true genius lay in the discovery that if the compression in the cylinder was reduced by closing the intake valve early, along with the piston not traveling all the way down during the intake stroke, as opposed to the full-length power stroke being longer, fuel efficiency would improve.
As hybrids are defined by efficiency and not power, the Atkinson philosophy is an ideal application in vehicles built around saving fuel and low emissions. While so-configured engines were deemed over-complicated and, by association, not cost-effective for mass manufacturing in the days of James Atkinson, today advanced materials and technology such as double-overhead camshafts and variable valve timing, exhaust gas circulation and clever ECUs - have turned his vision into a reality. Which is why modern hybrids no longer achieve the same goal by no longer relying on a shortened intake stroke, but simply keeping the intake valve open for longer when the combustion phase starts to reduce pressure.
With hybrids becoming an ever more common sight on US roads, CarBuzz decided to find the most efficient model currently on sale in 2025.
The downside of lower compression is lower power density and loss of ability to run high-octane fuels. Owing to that, there hasn't been much of a case to be made for Atkinson-cycle engines as standalone applications (although some Honda Civics used the technology in the 1980s); which is why Toyota implementing Atkinson technology paired with an electric motor to compensate for the loss of torque in the Prius - was the epiphany that re-established its viability as an ozone-friendly urban runabout.
But only after an American engineer named Ralph Miller decided to do something about the Atkinson engine's power shortage in 1957.
Nicolaus Otto (after whom the Otto cycle is named) and Eugen Langen founded the first company to produce internal combustion engines in 1864. While their names have arguably gathered some dust in automotive annals, their associates, Gottlieb Daimler and Wilhelm Maybach, were eternalized in the Daimler empire. Spare a thought, too, for James Atkinson, who, despite his breakthrough contribution to hybrid engines, never had a single car named after him.
As we now know, both the Otto and Atkinson renditions of the four-stroke engine suffer drawbacks.
So, in 1957, an American engineer called Ralph Miller honed the Atkinson concept ever further. His design focused on keeping the intake valve open for even longer as the air/fuel mix is sent into the intake manifold (or the first 20% to 30% of the compression stroke). He then made up for the associated loss in power owing to the shorter intake stroke with forced induction. The engine's efficiency gains are to be had by virtue of the cylinder never reaching maximum capacity through reduced pumping losses.
All things considered, the universe might have been a little unkind to James Atkinson following his discovery. Neither the automobile nor megacities existed in the late 1800s; no-one would have ever heard of the ozone layer and the horror of bumper-to-bumper traffic was an alien concept.
Essentially, the Atkinson engine was ahead of its time but an answer to a question that no-one had asked; and in the boomish wake of World War II in particular, no-one really cared about thermal efficiency in motorcars, let alone for saving the planet.
Toyota's new Prius is the best one by a mile.
Only once the world's economies became industrialized, commerce became urbanized and mass transportation became democratized, did cities (over)populate and mutate into asphalt jungles, their road networks today hopelessly unable to cope with the demands of millions of vehicles.
The stop/start nature of urban traffic makes hybrids the ideal vehicle for such conditions. The hybrid's tiny electric motor gets it off the line until the gas engine kicks in, and recharges under braking. Needless to say, a hybrid's tailored urban talents are shorn of their suitability the moment it hits the highway. In the absence of having to brake or coast, there's no opportunity to regenerate the battery.
Clocking 61 for a short stint in a 25 zone like in Horrible Bosses, then, is fine. You won't win (m)any drag races, but thanks to James Atkinson, at least the ozone gets to see another day.
2025-02-03T08:23:17ZSources:Autoweek.com, Enginelabs.com, Mechanicalboost.com, Toyota UK