GT40 Oil Again

[Teleman]

Why is the oil that PCM specs out suddenly no good? Wouldn't this be the obvious choice? After all, they design and expect the motor to deliver the best it can (I would hope). Why change the oil to something other?

[DanielC]

Short answer, the "new and improved" oils are not as good for older engines. Most oils are designed for auto engines, and autos have catalytic converters on them, and if your auto engine burns oil, it can poison the catalytic converter. Modern auto engines have a roller tappet camshaft that can live with out the high zinc and phosphorus additives required in a older flat tappet camshaft.
PCM has not changed the specs on oils required in their engines, the engine oils have changed.

[8122pbrainard]

Short answer, the "new and improved" oils are not as good for older engines. Most oils are designed for auto engines, and autos have catalytic converters on them, and if your auto engine burns oil, it can poison the catalytic converter. Modern auto engines have a roller tappet camshaft that can live with out the high zinc and phosphorus additives required in a older flat tappet camshaft.
PCM has not changed the specs on oils required in their engines, the engine oils have changed.

Excellent answer. I agree!