Now there's a short question with a looooong answer.
I ran Valvoline VR-1 20w50 initially. Changed at 45 minutes, 300 miles, and 1000 miles.
At 1500 miles I switched to Mobil 1 15w50.
I run a pre-luber and the Mobil 1 definately flows easier, as the pressure comes up quicker before starting. The motor actually seems a bit stronger on the Mobil as well.
I've run Mobil 1 in virtually everything I own for the past 10 years.
My Explorer has nearly 200K miles and uses less than 1/2 quart in 5000 miles. It still runs as strong as it did the day I bought it.
I roadrace a Legends car, and I often see 280 degree
oil temps and 10,000 RPM. So far, so good.
The viscosity depends on the bearing clearances in your motor and the temperatures you expect to see.
I use 10w30 year round in my stock street engines, and 15w50 in the Cobra and Legends car. (As well as the lawn mower and generator, being that they are air-cooled and run high
oil temps.)
The bearing clearances are set looser on the Cobra, but it still hits 90+psi at high RPM.
I'd recommend a quality
synthetic in any engine. I use the Mobil because it is available anywhere, and it has been around for decades and I've never heard anything bad about it. It's also one of the few true synthetics stilll available.
Later,