Oldsmobile 307 Engine

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By Mark Sabourin

In late 1980 Oldsmobile introduced it's newest small block, the 307ci/5.0L engine. It was available in the Riviera and Toronado cars to 1985.

The 307 was in production from 1980 to 1990 and was the only V8 not to receive a Fuel Injection option. From beginning to end it was only equipped with the Rochester 4-BBL Carburetor.

Two different VIN codes were used during the middle years. The "Y" was used in our cars and the "9" which was used in other cars such as the 442.

The differences between the older engines and the newer ones though not readily apparent, where quite major.

Up to and including most of 1984 the "Y" engine was equipped with the 5A heads p/n 22511238 and a conventional, standard bearing camshaft and cast iron heads and intake manifold which had rectangular ports both from the intake and into the exhaust.

In late 1984 and all of 1985 and beyond a roller lifter camshaft was fitted along with an aluminum intake manifold and different heads. The new heads were 7A p/n 22530557 and included bumps in the intake ports to agitate the air/fuel flow better and swirl grooves near the intake valves to increase the speed for even more mixing. There maybe some 6A heads out there but I think they were used on Canadian cars.

The later "9" engine was equipped with a roller lifter camshaft a year after the "Y" engine. It had the aluminum intake and 7A heads with "bumps" and swirls.

The early "Y" engine intake, heads, and exhaust are the best flowing and are used on many rebuilt late "Y" and "9" engines. The early "Y" heads can be identified by the "5A" embossing on them. The other, later heads are the "6A" and the more common "7A" heads.

During the 1983 to 1984 period there was an overlap between the two "Y" engines in which the 6A and 7A heads and manifolds were used with the conventional camshaft. I don't know how to identify these 1984 engines at this time except possibly by their production number.

Please note that all years in the following tables are inclusive and that part numbers are for A.C. Delco. Other part manufacturers can be substituted of course.

It must be emphasized that the Olds 307 is often confused with the Chevrolet 305 simply because they share the broader measurement of the 5.0 liter tag. They are not in any way similar or interchangeable.

Firing order: 1-8-4-3-6-5-3-2

Distributor turns Counter-Clockwise

Before checking the compression see this article: "Compression Testing"

• Ensure the battery is fully charged
• Remove spark plug wire from one plug and loosen the plug 1/2 turn.
• Re-install wire and repeat for each cylinder.
• Start and run the engine for a few seconds.

What this does:

• Loosens and blows any carbon on the spark plug nose out the exhaust.
• Hopefully blows debris from around the plug hole away.

Then:

• Remove all wires, keeping in order and all spark plugs.
• Perform Compression test cranking for at least 5 times/cyl.