You do not want the API Sm on the
oil at all. These oils are made for late model new engines. They use three engines to test the
oil. 2 that haveover head camshafts and no lifters and a V6 Chevy that has a wopping 2200 lbs open pressure. These oils have to meet the government standards and have a lot of detergent and very low
zinc in them. The
zinc and other additives that you find in the Penn and Jo Gibbs
oil will clog up the conveter sooner as well and they have to warranty them for like 150,000 miles now.
You do not want to run any oil with the APi sticker on it in a high perfmance engine or for sure in a flat tappet engine. Buy a damn oil made for a high performance application and be done with it. Everybody has an opinion on this but I have lived it and seen how it works by dyno testing, running and taking apart engines. The new oil is crap for an early engine or high performance engine. I have inspected engines that we have ran the Jo Gibbs oil in and swear by it. Less wear on the cylinder, bearings, cam and everyother part in the engine.
What I always find funny is these guys that are going to buy a 10,000.00 to 40,000.00 engine and then complain about the oil cost. The good stuff is only about 30 to 40 percent more and will make your engine last longer and generally do not have to change as often.
Good luck, Keith Craft