Your Guide to the History of Harley-Davidson Engine Types

Harley-Davidson® Engine Types

1909 Atmospheric V-Twin

With its cylinders arranged at a 45-degree angle, this first V-Twin engine would establish a key design element that endures today. This engine displaced 49.5 cubic inches and made about 7 hp. It unfortunately proved to be sometimes unreliable and was only offered for a single year.

1911-1929 F-Head V-Twin

Harley’s second attempt at a V-Twin engine was a winner. With an improved valve train, waterproof ignition and displacement of 61 cubic inches, the new engine was reliable and powerful. Displacement would later be increased to 74 cubic inches.

1929-1973 Flathead V-Twin

The side-valve Flathead engine would prove to be a durable workhorse, and the engine that powered Harley-Davidson® military models through World War II. Initially offered as the D model 1929 with 45 cubic inch displacement, a 74-cubic inch V model was offered in 1930 as the new hot engine in the Harley® line. In 1937 U and UL models were powered by 74 cubic inch Flatheads while UH and ULH received an 80 cubic inch version. The Flathead engine powered the Harley-Davidson® Servi-Car utility trike until 1973. Harley fans, inspired by its finned, flat cylinder heads, gave this engine its Flathead nickname.

1936-1947 Knucklehead

The first overhead valve Harley-Davidson® engine was nicknamed the Knucklehead by Harley fans who thought its rocker covers and pushrod tubes looked like a clenched fist. The first E model engine retained the signature Harley® 45-degree cylinder angle and displaced 61 cubic inches, and a 74-cubic inch version would appear later. The Knucklehead engine introduced the basic architecture for all future air-cooled V-Twin Harley-Davidson® engines.

1948-1965 Panhead

Updated with aluminum cylinder heads, hydraulic valve lifters, improved oiling and crank pin roller bearings, this second-generation Big Twin was 8 pounds lighter than the Knucklehead. Displacement remained 61 and 74 cubic inches. Once again, Harley fans gave the new engine a nickname – Panhead for the new stamped rocker covers that looked to some like cake pans.

1957-1985 Ironhead Sportster®

Designed for the new XL Sportster® model, this 55-cubic inch V-Twin engine featured 45-degree cylinders, overhead valves, aluminum pistons and a hemispheric combustion chamber. The Ironhead Sportster was a “unit” engine, with the transmission located in the same case as the engine, and featured a foot shifter. Its iron cylinder heads earned it its nickname – the Ironhead.

1966-1984 Shovelhead

Introduced with the first Electra Glide® model, this update to the Big Twin engine featured improved aluminum cylinder heads, stronger valves and pistons, and a 12-volt electrical system. Offered in 74- and 80-cubic inch displacement, the Shovelhead engine nickname came from the shape of the new rocker covers, which either look “shoveled out” or resembled the shape of an old-time coal shovel.

1984-1999 V2 Evolution® Engine

All-new and the first Harley® engine created using computer-aided design, the 80-cubic inch “Evo” retained the classic 45-degree layout and overhead valves with pushrods, but was equipped with aluminum cylinders and heads, a new ignition system, and a combustion chamber that made power on lower-quality unleaded fuel while improving fuel economy. Advances in design and manufacturing made this new engine oil-tight. The 1995 Electra Glide® Ultra Classic® model offered an Evolution® engine with electronic fuel injection, a first for Harley-Davidson. The Evolution engine is known for being stout and reliable.

1986-2022 Sportster® Evolution® Engines

This new unit engine for Sportster® models featured a single camshaft and many design elements derived from the V2 Evolution® Big Twin engine. Initially offered with 1100cc displacement, later versions of the Sportster Evolution engines were either 883cc or 1200cc engines.

1999-2017 Twin Cam™

Named for its dual camshaft design, this new V-Twin boasted 88 cubic inch displacement and shared only 18 parts with the Evolution engine it replaced. The Twin Cam’s displacement would eventually grow to 110 cubic inches. New cylinder heads, valves and intake/exhaust ports optimized emissions, economy and performance. The B series Twin Cam™ engines featured a counter-balancer to reduce vibration in rigid-mount Softail® models.

2002-2017 Revolution® V-Twin

Introduced for the new VRSCA™ V-Rod® model motorcycles, the 69 cubic inch (1131cc) Revolution® engine was a radical departure from previous Harley-Davidson® engine design. Developed with the assistance of Porsche, the Revolution V-Twin's twin cylinders were splayed at a 60-degree angle and topped with dual overhead camshafts and four-valve heads. The Revolution V-Twin engine was liquid cooled and internally counter-balanced, fuel injected, and with 11.3:1 compression made 115 hp at 8200 rpm – new benchmarks for a Harley-Davidson® production engine. 

2012-Present Screamin’ Eagle® Crate Engines

Engineered by the pros at Harley-Davidson, this series of complete high-performance engines offer a bolt-in solution for riders looking for no-compromise power. Screamin' Eagle® Crate Engines are engineered and tested as a complete collection of high-performance components and backed by a factory warranty when installed by an authorized Harley-Davidson® dealer. The crate engine program was launched with the 120-cubic inch Screamin’ Eagle® Twin-Cam™ 120R and continued after the 2017 introduction of the Milwaukee-Eight® engine family, reaching its current apogee with the 2023 launch of the Screamin' Eagle® 135ci Stage IV Performance Crate Engine.

2017-Present Milwaukee-Eight® V-Twin

An all-new design, the Milwaukee-Eight® engine features the return to a single camshaft, but with four-valve cylinder heads (two exhaust and two intake valves for each cylinder) for a total of eight valves, the inspiration for its name. All versions are counter-balanced to reduce vibration, and some versions feature Twin-Cooled™ liquid-cooled cylinder heads. Initially offered with 107- and 114-cubic inch displacement, displacement has grown to 121 cubic inches in regular production, with variable valve timing introduced in 2023. With its traditional 45-degree cylinder angle, the Milwaukee-Eight® V-Twin engine retains the classic look/sound/feel of a Harley-Davidson® V-Twin engine.

2021-Present Revolution® Max V-Twin

Representing a new generation of Harley-Davidson power, the Revolution® Max engine family was launched in the Pan America® and Sportster® S models. This 60-degree liquid-cooled V-Twin was designed to function as a stressed member of the motorcycle chassis to reduce overall motorcycle weight. The Revolution Max V-Twin engine is optimized for light weight and a broad powerband that builds to a rush of high-RPM power. It features double overhead camshafts, four-valve cylinder heads, variable valve timing, dual downdraft throttle bodies and is counter balanced to reduce vibration. The engine and six-speed transmission share a common case. The Revolution® Max is offered with 1250cc and 975cc displacement.