Harley-Davidson engine timeline

The classic Harley-Davidson engines are two-cylinder, V-twin engines with the pistons mounted in a 45° "V". The crankshaft has a single pin, and both pistons are connected to this pin through their connecting rods.[6]

The design causes the cylinders to fire at uneven intervals. This is an engineering tradeoff to create a large, high-torque engine in a small space. This design choice is entirely vestigial from an engineering standpoint, but has been sustained because of the strong connection between the distinctive sound and the Harley-Davidson brand. This design, which is covered under several United States patents, gives the Harley-Davidson V-twin its unique choppy "potato-potato" sound. To simplify the engine and reduce costs, the V-twin ignition was designed to operate with a single set of points and no distributor. This is known as a dual fire ignition system, causing both spark plugs to fire regardless of which cylinder was on its compression stroke, with the other spark plug firing on its cylinder's exhaust stroke, effectively "wasting a spark". The exhaust note is basically a throaty growling sound with some popping. The 45° design of the engine thus creates a plug firing sequencing as such: The first cylinder fires, the second (rear) cylinder fires 315° later, then there is a 405° gap until the first cylinder fires again, giving the engine its unique sound.[76]

Harley-Davidson has used various ignition systems throughout its history - be it the early points/condenser system, (Big Twin up to 1978 and Sportsters 1970 to 1978), magneto ignition system used on 1958 to 1969 Sportsters, early electronic with centrifugal mechanical advance weights, (all models 1978 and a half to 1979), or the late electronic with transistorized ignition control module, more familiarly known as the black box or the brain, (all models 1980 to present).

Starting in 1995, the company introduced Electronic Fuel Injection (EFI) as an option for the 30th anniversary edition Electra Glide.[77] With the introduction of the 2007 product line, EFI is now standard on all models, including Sportsters.[78]

In 1991, Harley-Davidson began to participate in the Sound Quality Working Group, founded by Orfield Labs, Bruel and Kjaer, TEAC, Yamaha, Sennheiser, SMS and Cortex. This was the nation's first group to share research on psychological acoustics. Later that year, Harley-Davidson participated in a series of sound quality studies at Orfield Labs, based on recordings taken at the Talladega Superspeedway, with the objective to lower the sound level for EU standards while analytically capturing the "Harley Sound."[citation needed] This research resulted in the bikes that were introduced in compliance with EU standards for 1998.

On February 1, 1994, the company filed a sound trademark application for the distinctive sound of the Harley-Davidson motorcycle engine: "The mark consists of the exhaust sound of applicant's motorcycles, produced by V-twin, common crankpin motorcycle engines when the goods are in use". Nine of Harley-Davidson's competitors filed comments opposing the application, arguing that cruiser-style motorcycles of various brands use a single-crankpin V-twin engine which produce a similar sound.[79] These objections were followed by litigation. In June 2000, the company dropped efforts to federally register its trademark.[80][81]
Electra Glide "Ultra Classic" in Bristol
[edit] Big V-twins

* F-head, also known as JD, pocket valve and IOE (intake over exhaust), 1914–1929 (1000 cc), and 1922–1929 (1200 cc)
* Flathead, 1930–1948 (1200 cc) and 1935–1941 (1300 cc).
* Knucklehead, 1936–1947 61 cubic inch (1000 cc), and 1941–1947 74 cubic inch (1200 cc)
* Panhead, 1948–1965 61 cubic inch (1000 cc), and 1948–1965, 74 cubic inch (1200 cc)
* Shovelhead, 1966–1984, 74 cubic inch (1200 cc) and 80 cubic inch (1345 cc) since late 1978
* Evolution (a.k.a. "Evo" and "Blockhead"), 1984–2000, 80 cubic inch (1340 cc)
* Twin Cam 88 (a.k.a. "Fathead") 1999–2006, 88 cubic inch (1450 cc)
* Twin Cam 88B (counter balanced version of the Twin Cam 88) 2000–2006, 88 cubic inch (1450 cc)
* Twin Cam 95, since 2000, 95 cubic inch (1550 cc) (engines for early C.V.O. models)
* Twin Cam 96, since 2007, 96 cubic inch (1584 cc)
* Twin Cam 103, 2003–2006, 2009, 103 cubic inch (1690 cc) (engines for C.V.O. models), Standard on some 2011 Touring models such as the Road King Classic and Road Glide Ultra and optional on other Touring Models like the Road Glide Custom and Street Glide.
* Twin Cam 110, since 2007, 110 cubic inch (1802 cc) (engines for C.V.O. models)

Evolution Sportster cruising around downtown Buenos Aires
[edit] Small V-twins

* D Model, 1929–1931, 750 cc
* R Model, 1932–1936, 750 cc
* W Model, 1937–1952, 750 cc, solo (2 wheel, frame only)
* G (Servi-Car) Model, 1932–1973, 750 cc
* K Model, 1952–1953, 750 cc
* KH Model, 1954–1956, 900 cc
* Ironhead, 1957–1971, 900 cc; 1971–1985, 1000 cc
* Evolution, since 1986, 883 cc, 1100 cc and 1200 cc

V-Rod on the show room floor
[edit] Revolution engine

The Revolution engine is based on the VR-1000 Superbike race program, developed by Harley-Davidson's Powertrain Engineering team and Porsche Engineering in Stuttgart, Germany. It is a liquid cooled, dual overhead cam, internally counterbalanced 60 degree V-twin engine with a displacement of 69 cubic inch (1130 cc), producing 115 hp (86 kW) at 8250 rpm at the crank, with a redline of 9000 rpm.[82][83] It was introduced for the new V-Rod line in 2001 for the 2002 model year, starting with the single VRSCA (V-Twin Racing Street Custom) model.[84][85]

A 1250 cc Screamin' Eagle version of the Revolution engine was made available for 2005 & 2006, and was present thereafter in a single production model from 2005 to 2007. In 2008, the 1250 cc Revolution Engine became standard for the entire VRSC line. Harley-Davidson claims 123 hp (92 kW) at the crank for the 2008 VRSCAW model. The VRXSE Destroyer is equipped with a stroker (75 mm crank) Screamin' Eagle 79 cubic inch (1300 cc) Revolution Engine, producing over 165 hp (123 kW).