Are inline-5s the ultimate engine outcast?

Fours, sixes, and eights—even numbers dominate when it comes to cylinder counts in automotive piston engines. It’s no coincidence either, as the lack of odd-numbered configurations can be blamed squarely on Newton’s Third Law of Motion. Motors with three, five, or seven cylinders are just more difficult to balance out; you really do want the same number of pistons traveling in each direction at any given time.

These challenges, however, haven’t stopped engineers from experimenting with different setups over the years, largely to address packaging constraints and power demands in legacy-platform vehicles. It’s led to some pretty wacky creations, including the inline-5, an engine literally bridging the gap between its I-4 and I-6 siblings. Physics be damned, though, it’s been the powerplant of choice for some truly interesting rides throughout the years, all while sounding like a V-10 chopped in half. Here are seven of our favorites.

Mercedes-Benz 300D

Mid-1970s Mercedes are famous for being as rugged as they are handsome, but did you know these beasts were the first time an inline-five was offered in an automotive application? It’s true, the Benz 240D 3.0 (also referred to as the 300D) was first to market with a five-cylinder engine in 1974. The 3.0-liter OM617 diesel delivered just 80 horsepower, which seemed a little conservative even at the time, but it made up for a lack of grunt with bulletproof reliability and decent fuel economy. These engines proved so indestructible that their production run lasted a full 17 years, finally ending in 1991. You’ll find them in the garages of collectors, and the taxi lanes of African airports, today.

Audi TT RS

Launched in 2009, Audi’s TT RS is a pure more-for-your-money proposition, especially when compared to its big brother, the R8. The TT’s turbocharged 2.5-liter produces a healthy 400 horsepower, catapulting the compact sports coupe to 60 mph in just 3.4 seconds. A $65,000 base price might not seem like a bargain, but it’s a full $100,000 under the V-10 R8. You get similar styling, hot performance, and one of the most unique exhaust notes on the market today.

Volvo 850 T5-R

Quite possibly the ultimate 1990s sleeper, the Volvo 850 T5-R is the go-to box on wheels for those seeking mundane looks and stupid-quick speed. Offered in both sedan and wagon body styles, the “turbo brick” was equipped with a turbocharged, 245-horsepower inline-5. Despite the blocky aerodynamics, it was still capable of over 150 mph, a nasty surprise for any would-be sports car challengers. It might not have been the first five-cylinder car ever produced, but the T5-R is so iconic that it’s surely the first one that’ll come to mind.

Acura Vigor

Honda’s luxury division might be known for their naturally aspirated V-6 offerings, but the early-1990s Acura Vigor shows what happens when your flagship has just 2.7 liters of bent-six power and you want to protect its brand positioning. Under the hood was a 2.5-liter inline-5  mounted front to back, Audi-style, that sent just under 200 horsepower to the front tires. While the setup proved innovative, the stiff competition from Lexus and poor sales ultimately ended this rare car’s stint in the U.S. after only 2 model years. It continued in Japan as the Accord Vigor; the next generation became our 2.5TL, which also featured a longitudinally-mounted inline-five,

Ford Focus RS (MK 2)

It’s only fitting that Ford’s europe-only, Mk 2 Focus RS featured one of the strangest powerplants to grace the hot hatch segment. The 2.5-liter Duratec five-cylinder engine was actually a derivative of a Volvo design, augmented with an air-to-air intercooler, forged crank, and special pistons to withstand 20 psi of boost pressure provided by the BorgWarner turbo. Peak power was 301, allowing the car to hit 60 mph in under 6 seconds. It’s a shame we didn’t have the opportunity to experience this warbly five-banger on our side of the pond, as it’s U.S.-bound successor came with a more-powerful, but decidedly less-crazy turbo-four.  

Land Rover TD5 Discovery II

Created in response to increasingly-stringent Euro III emissions standards, Land Rover’s TD5 proved itself to be just the workhorse that was needed for any off-road adventure. The 2.5-liter diesel was launched in 1998 and delivered 122 horsepower and a punchy 221 lb-ft of torque, all while meeting the updated pollution requirements. Production of the inline-five lasted until 2004, but a robust aftermarket has sprouted around the engine, due to its stout durability record and easily-tunable electronics.

Honda RC149

At just 124-cc, this Honda’s powerplant is by far the smallest on our list, but it’s also attached to the lightest vehicle—the RC149 racing motorcycle. The tiny five-banger was developed for the 1965 Japanese Grand Prix, offering 34 horsepower and revving to an insane 21,000 rpm. Top speed was over 135 mph, making it the fastest bike in its class for the 1966 season. It was also the best sounding too, with a high-pitched scream seldom heard outside the realm of Formula 1. Examples of these bikes are exceedingly rare, but video clips of these little racers hitting redline will surely have your hair standing on end.