Thanks for the presentation. It is a good read. What is interesting to me is the 216 hour test that was aborted at 168 hours due to sludge build up - this is right to my point. At 60mph that's over 10,000 miles without an oil change. At 35mph it's the better part of 6000 miles.
What I struggle with in this debate is coming up with 'best' oil for a filter-less, modified, flat-tappet antique engine - as well as the proper service interval for it when installed in a hobby car.
There's an author in the UK that is an interesting read on the topic:
Car Bibles in particular the comment: "As I touched upon above, oils with a CG and higher rating typically don't contain enough ZDDP, and the replacement friction modifiers don't work in highly loaded valve trains (generally older engines especially those with 2V design). If you try to compensate by adding a ZDDP additive into a newer oil it still might not work because of interactions with other additives in the oil."
This is what has me circling back to the idea of buying an economical API SA base stock and adding just the right amount of ZDDP needed for the valve train (not to mention the anti-oxidant properties). Essentially a home blended API SB oil.
With very frequent oil changes the dirt deposited in the pan will be the first to drain off when the plug is pulled. Long before it can turn to sludge.
PS. Love your website on the Slant Six. The practical experimentation with carburetors is spot on.
