minivette, I hope you like consistency because I’m going to agree with pretty much everyone else above. The oil did a decent job (forget about that copper … most likely from assembly lube and/or the oil cooler) but the TBN of 6.4 is nothing to crow about nor is a 10W30 oil which has thinned in less than 5,000 miles. If I were writing for Blackstone, I probably would
not have added the comment telling you that an increased interval is OK. Yours is a specialty car/engine and extending drain intervals until the oil utterly fails is pointless.
If you decide to stay with Royal Purple (price, local availability, some other reason … ), I’d try and stick with 4,000 miles as a maximum interval. If you want to go longer between drains (5,000+ miles), the only oil I’d recommend is Red Line (in the same weight). If it were my machine and I wanted to treat it to frequent changes (say 2,500 – 3,000 miles - which is probably what I’d do), I’d use Schaeffer Supreme 7000 10W30 synthetic blend. Stable base oil and a killer additive package make for
extremely low wear. At $3 per quart, the extra changes should still allow you to make the payments on your pricey toy.
Mobil 1 or Amsoil? I’d use that for 4,000 miles and then test before going any longer with it.
“How did Royal Purple get to be a motor oil used in racing … ?”
Mystic, in SCCA, most racers use Red Line Oil. A few (supposedly) use other brands including Valvoline, Mobil 1 and Royal Purple … but I think RP’s racing reputation is mostly played up in their advertising … and their racing formula is very different from their street formula.
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Bror Jace