I did have the intake off at one point.....I honestly don’t remember if the heads were rival or oval....just don’t know...sorry.
Wix oil filter 51060xp
I know who the builder was....I can ask about the bypass. They probably won’t know..
More important to get the actual oil pressure numbers. I will be able to check next week.
I’m not opposed to just using the Valvoline VR1 synthetic.....was hoping for verification that’s ok...
I do like the Mobil1 idea. I need to think on that a bit....I hesitate only because if it was built to 1971 OEM specs, that might be too thin...ok for newer spec motors....older....not so sure.
We always ran 10w30 or 10w 40 in Chevy v8s here....years and years...lnot unwilling to change, but need to think on it.
A 0W-40 is more viscous than a 5W-30 or 10W-30 until you get down to sub-zero temperatures. The 0W-xx winter rating doesn't thicken as much in extreme cold weather as the 5W-xx and 10W-xx oils do.
The first number doesn't represent the operating viscosity. It references the minimum temperature at which the oil is still pumpable (dynamic viscosity) with varying targets for each winter grade. Hence, the "W" stands for winter. (expressed in centipoise (cP))
0W-xx = -31°F (-35°C)
5W-xx = -22°F (-30°C)
10W-xx = -14°F (-25°C)
15W-xx = -6°F (-20°C)
20W-xx = 4°F (-15°C)
The second number is the actual oil grade at operating temperature. It's based on the kinematic (pouring) viscosity at 212°F. (expressed in centistoke (cSt))
xW-20 = 6.9 - 9.2 cSt (HTHS = ≥2.6 cP)
xW-30 = 9.3 - 12.4 cSt (HTHS = ≥2.9 cP)
xW-40 = 12.5 - 16.2 cSt (HTHS = ≥ 3.5 cP for 0W-40 and 5W-40 grades, ≥3.7 cP for 10W-40 and 15W-40)
xW-50 = 16.3 - 21.9 cSt (HTHS = ≥3.7 cP)
The HTHS is the high temp, high shear rating measured in dynamic viscosity at 150°C. Each grade has a minimum but no maximum.
A 0W-40 is required to be <6,200 cP dynamic viscosity at -35°C, have a kinematic viscosity between 12.5 and 16.2 cSt at 212°F, and an HTHS rating of ≥3.5 cP.
A 10W-30 is required to be <7,000 cP dynamic viscosity at -25°C, have a kinematic viscosity between 9.3 and 12.4 cSt at 212°F, and an HTHS of ≥2.9 cP.
The 0W-40 can withstand both lower temperature and higher temperature than the 10W-30 in most cases. Above ~10°C, the first number is largely irrelevant. There's other factors like shear stability, Noack volatility, etc... that comes into play with different grades, but that's a whole different can of worms.