[rotorwrench]

When new, the flathead V8 used SAE 20W20 or SAE 30 engine oil depending on winter or summer operation. Now days it would be more like SAE 10W/30 on an overhauled engine for year round operation. An old loose motor would like more viscosity to keep the pressure up.

Any oil is better than none. Non detergent is for break in so that there are no friction modifiers but a person shouldn't run it more than 500 miles or so before switching to detergent oil. If a person doesn't know the history of the engine, they should start out with frequent oil changes with detergent oil whether there is a filter or not. Oil is cheep compared to an overhaul with a ruined crankshaft. Drain engine oil imediately after a complete warm up so the oil can carry all the crap out before it settles to the bottom again.

Studebaker Technical Products (STP) viscosity buillder was for worn & loose engines. It also works well mixed with regular oil as a build up lubricant at overhaul. It keeps the lubricant on the parts longer prior to start up. Other than that, I would have no use for it. It's too much like molasses in texture and takes forever to get it in or out of a gearbox.