The Differences Between Odd Fire and Even Fire Intake Manifolds in a Buick V6


The history of the Buick V-6 engine dates back to the 1962 model year, when the first V-6 was installed in the Buick Special. Two variations of the Buick V-6 emerged. Their intake manifolds determined their characteristics. One version of V-6 was known as the “odd-fire” and the other was known as the “even-fire."

Engines Types

  • The odd-fire V6s, which had uneven firing impulses, were the first V6 engines built by Buick. They were manufactured from 1962 to 1977. Their firing impulses created a distinct exhaust rumble.

    The even-fire V6s had spark plugs that fired at evenly timed impulses. This V6 is still used in the modern Buick. The origins for this engine can be traced back to the middle of the 1977 model year. The even-fire V6 has a smoother idle than the odd-fire V6.

Odd Fire Manifolds

  • The odd-fire engines’ intake manifolds used separate runners. The left runner fed the left side of the manifold, which fed the left cylinder bank. The right side fed the right cylinder bank. The channels inside the intake manifold were narrow to keep the fuel/air mixture flowing freely at low speeds for good atomization. Two-barrel carburetors fed the fuel/air mixture into the manifold. Odd-fire intake manifolds were used on the earliest Buick V6 engines. These manifolds fit engines with a 90-degree angle between the cylinder banks.

Even Fire Manifolds

  • The intake manifold of the even-fire Buick V6 uses a large chamber to route the fuel/air mixture into the cylinder banks. The manifolds are used on engines with a 60-degree angle between the cylinder banks. The turbo 3.8-liter and the 4.1-liter V6 use four-barrel carburetors.

1980s Changes

  • The V6 intake manifold was redesigned in 1979 so the fuel/air charge could be entered into the combustion chamber with less restriction. In 1981, Buick employed the use of aluminum intake manifolds for the V6 to make cold engines more drivable. A thermal vacuum valve was used for the choke and an Early Fuel Evaporation (EFE) system helped vaporize the incoming fuel/air mixture. Computer Command Control, an onboard computer, regulated the fuel/air mixture.

    By 1986, the V6 intake manifold was modified for electronic fuel injection applications. The multi-port fuel injection introduced the fuel/air mixture into intake ports for the 3.0-liter engine. The intake manifold delivered the air from the intake system.

Recent Changes

  • The Buick V6 employed the use of plastic intake manifolds during the 1990s. According to the 1995 Buick sales brochure, this effort was used to make the building process more environmentally friendly.

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