Synthetic Oil?

[solidaxle]

Originally Posted by lotsagas4u

The Valvoline VR-1 is great break-in oil, as it contains a good amount of zinc, which is needed for flat tappet cams. But it does not contain much detergent, so sludge build up could be a concern if you expect to run the engine for 50,000 miles,
There are two versions of this oil, one in black container, low detergent, silver container, normal detergent, both high in zinc.

To expand on your statement.
The black container is synthetic as stated on the label. The gray container does not mention anywhere that it is synthetic. It states for racing and classic cars "Specially designed for push-rod & flat- tappet engines".