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Before 1971, all Oldsmobile street engines require lead. An engine uses lead for valve seat protection and octane boosting. GM states in the 1971 Owner's Manuals that all 1971 GM engines can safely use unleaded fuel. You might want to consider that 100,000 miles on an unopened engine wasn't a common occurance back then.

The lead (actually tetraethyl), when burnt in the combustion process is deposited on the valve seat. This cushions the softer metal of the pre 1971 heads. Without the lead the harder valve slams into the unprotected seat and will cause seat recession. This leads to burnt valves. Heads with soft seats are A - F. Heads with hard seats are G - K.

Studies made on pre-71 engines showed that unleaded gas normally would not be horrific to your engine unless you were at sustained high rpms, such as drag racing, or using 6.13 gears on the street or something similar. Theoretically, an engine running on no-lead will need a valve job sooner than one running leaded, even under normal driving. But no-one I know of, including myself, have ever run across this no-lead curse.

Heads without hard seats will go about 60,000 miles on unleaded gas. In a car that will see a lot of driving, you will need the hardend seats installed. Valve recession is apparently not a big problem for street-driven cars. Though the lead is gone, there are additives in gasoline today that perform much of the same lubricating function. The only time you absolutely need hard seats are on an engine that is not going to be apart for a longer duration than that. All these shops that insist on hard seats do so because they sell/install them.

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Use a fuel additive that contains lead if (1) your heads are pre 1971, (2) your compresion ratio exceeds 10.1, (3) you have no catylitic converters, and (4) you rev past 3 grand regularly.

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