I suppose I should have mentioned that clearances range from .0025-.0035. The engine has probably 5k road miles and about 30 track passes, so it's broke in. With my clearances, zero or 5 weight is not something I want to go to. I've been using Rotella 15w-40, but I think they've dropped some of the zinc additives from their newest blends. As usual though, details are hard to come by. Mobil is pretty open about their blends and zinc content, at least on their website. My concern is for the flat tappet cam.
Doug,
I emailed both Shell and Chevron to ask about ZDDP levels in their diesel oil (Rotella and Delo) as I was figuring out what to run in my new 470 FE with flat hydraulic tappets. Chevron reduced their ZDDP from ~1200 to 800 ppm and added other additives (ash?) to compensate while meeting EPA standards. Shell Rotella still has 1200 ppm ZDDP. I have no idea why Shell is able to make their higher zinc additive compliant while Chevron (and other companies) couldn't.
A member of our Cobra club was a development engineer for Chevron in charge of their racing program for many years. He convinced me that the 1200 ppm ZDDP diesel oil is the best for performance engines (claims even race teams sponsored by Penzoil, etc. used Chevron Delo because it flat worked in race conditions). He recommended using Delo, but adding ZDDP additive since the Delo now has reduced zinc. I understand his loyalty to Chevron, but that seems a little silly when I can get Rotella that already has the right zinc level in it. I'm planning to use the Rotella starting my first oil change. Given the relatively low mileage my Cobra will see, I figure dino makes more sense since I'm going to want to change the oil every 3k anyway.
I'll close by saying that the whole oil thing is a mystery, in large part because of the proprietary nature of the compounds. There's a whole lot of opinions, but the only folks that really seem to have data are the oil companies, and they wrap marketing-speak around everything.
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