I've learned that
Synthetic oil (Mobile One or Syntec) are best for street use, but cut with 20/25% regular
oil to keep the engine gaskets from drying out and getting too brittle. My 1990 Ford F150 w/302 used Mobile One since new (5000 miles of Kendall GT1 for break-in) and currently has 221,000 miles without any major engine problems. The only problems I had was the drying out and deterioration of the engine gaskets. After about 150,000 miles, I cut it with regular 10/30 or 10/40
oil and found it to be successful. I'll use 10/40 Syntec with one or two qts. straight Castrol 10/40 and change it every six months, like I do with my Corvette 350. Any
synthetic is good for street use but doesn't stick to the cylinder walls and cam journals well when sitting for long periods.
Hey Art. I just got my ERA Cobra back from Tony's. It's done in Black...see my gallery. You gotta stop by sometime.
Rich