6 Best Harley-Davidson Engines in History

Best of the Best

With a history that spans well over a century to this point, Harley-Davidson has built its fair share of iconic motorcycles - and engines - over that timeframe, as one might imagine. Narrowing down that list to determine the "best" of the bunch is never an easy task, but these six H-D powerplants stand out above the pack for a few notable reasons. 

Photos: Harley-Davidson

Flathead

First up, we have the Flathead, which originally debuted in 1929 in a time when Harley was facing stiff competition from Indian and other up-and-coming makes. Cheaper to build than more complicated overhead valve engines, the Flathead became a legend in the ensuing years, powering a long list of motorcycles until it was finally discontinued in 1973 - marking an improbable, nearly half-century run. 

Photos: Harley-Davidson

Ironhead

The Ironhead came along in 1957 and enjoyed its own long production run, sticking around until 1985 and playing a major role in the success of the legendary Sportster, too. In fact, the Sportster's Ironhead was the first Harley engine to tout one horsepower per cubic inch of displacement, and in the ensuing years, it became quite popular with those looking to extract more speed from their bikes, too. 

Photo: Ironhead Cycle

Evolution Twin (Evo)

The Evolution Twin (Evo) joined Harley's lineup in 1984 and was one of the ways that MoCo managed to revive itself after the years it was owned by American Machine and Foundry (AMF), which nearly ran it into the ground, financially speaking. The Evo helped bring Harley into the modern age and saved it from collapse with its aluminum components and air-cooled construction, and wound up hanging around in the Sportster through 2022, in fact. 

Photos: Harley-Davidson

Twin Cam

The Twin Cam 88 came along in 1999 as a way to instill more power in bigger bikes, but the double-overhead-cam (DOHC) powerplant faced its fair share of problems from the start. However, the Twin Cam 96 and 103 that followed proved to be major upgrades and soon expanded across H-D's lineup, and left quite a positive impression before giving way to the newer Milwaukee-Eight. 

Photos: Harley-Davidson

Milwaukee Eight

Speaking of the Milwaukee-Eight, it has since become H-D's powerplant of choice for a wide berth of motorcycles and is only the third clean-sheet redesign in its history. Thus far, the M8 has proven to be very reliable while also generating impressive power and doing so while emitting fewer pollutants, which makes it a win-win in just the few short years it's been on the market. 

Photos: Harley-Davidson

Revolution

Then there's the Revolution engine, which is a bit interesting in that it was partly developed by Porsche before landing in the beloved V-Rod, or VSRC. The water-cooled powerplant features quite the modern design of its own and was based on the engine present in the VR1000 Superbike, which makes it both cool and rather special at the same time - and it has since given way to the brand-new Revolution Max, too.

Photos: Harley-Davidson

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