Reference Manual

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Chapter 1: Engines: Oldsmobile V8s: Differences between the Y and 9 engines

A total of four basic Oldsmobile 307 engines were installed in Oldsmobile G-bodies. Early engines had regular flat hydraulic lifters and later engines used roller lifters with shorter pushrods and matching camshaft. There are also performance versions of both types. The chart below outlines the model years each type of engine was used:

There are surprisingly few differences between the Y and 9 engines. The camshaft and dual-snorkel air cleaner are the only power "adders" in the engine and the rest of the part differences are in place to allow for higher rpm use the 9 engines will most likely see. Below is a chart which outlines these parts:

The 307-9 spends much more time in the upper rpm band than the Y versions do because of the rear axle ratio. All Hurst/Olds and 442 models got an 8.5" (except for 1983, which had a 7.5") ring gear which had a ratio of 3.73:1 with the pinion gear. This gear was a big part of the performance of these cars. The 307-9 versions are rated at 30 horsepower more than the Y and 5 lb/ft fewer than the Y (likely due to the camshaft).