1986 Oldsmobile 307 Specifications

by Henri Bauholz
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From 1980 until 1990, Oldsmobile made a 307-cubic-inch, eight-cylinder engine that was capable of producing between 140 and 180 horsepower. The 307 went into nearly all '80's Oldmobiles, including the Delta 88s, Cutlass/442, 98s and Toronados. The 307 also went into other GM cars such as the Buick, Pontiac, Cadillac and Chevy. For the duration of the 307 engine's production, it had a four-barrel carburetor. This small block V8 was one of the many Oldsmobile Rocket 8 engines, noted for interchangeable parts and producing a relatively high torque at low rpm.

The Block and Carburetor

The V8 307(5.0 liters) engine block for the 1986 Oldsmobile is a 90 degree V8 engine. The engine has a bore diameter of 3.800 inches and a stroke of 3.385 inches. The compression ratio is 8.0: 1. Oil capacity is 5 quarts, including the filter, and oil pressure is 30 psi @ 1500 rpm. The carburetor is a Rochester Quadrajet four-barrel with a primary Venturi of 1 3/32", a primary bore diameter of 1 3/8" and a secondary bore diameter of 2 1/4".


The Rocker arm ratio is 1.6:1. Intake and exhaust valve lifter distances are 0.4 inches for hydraulic models and 0.395 and 0.402 inches respectively, for roller types of lifters. The Cam bank angle was 39 degrees and the diameter of the lifters was 0.921 inches. Camshafts were usually interchangeable with other small block Rocket 8 engines, but not applicable for use in more modern Oldsmobile units.

Valve Train

All 5A and 7A heads for the 307 have a lifter bank angle of 39 degrees and lifter diameter of 0.842 inches, and a pushrod length of 8.265 inches for hydraulic models. Engines with roller lifters have a 0.921 lifter diameter and a 7.718 pushrod length. Spring free length is 1.960 inches or 2.090 inches, depending on whether the engine is a Type Y or Type 9.


Besides having two types of lifters, the Oldsmobile 86 307 cubic inch motor has two types of heads and two types of engines. The head's labels are 5A and 7A, while the engines are Type Y and Type A. With 67cc of combustion chamber volume and an intake port height of 2.03 inches, the 5A heads were slightly larger than the 7A heads. Both heads had an intake port width of 1.30 inches, an intake valve size of 1.75" and exhaust valve size of 1.50". The Y and 9 type engines had only minor differences.

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