I've used this site in the recent past as a reference as there is LOTS of great info here... I bought my first ever Blazer last week

... a 1978 K5 Cheyenne... it's a great little truck and I'm super proud of her, but it runs like crap... so I decided the best fix was a top end rebuild with new cam, intake, and headers... and a complete tune up and carb rebuild (my wife thought it was overkill but seemed reasonable to me)... the lady I bought it from put an Edelbrock 600cfm quadrajet on it but didn't tune it and left a few vacuum lines off or loose... so, I picked up my new Comp Cams camshaft and lifters yesterday and the dude at the shop said I couldn't use ANY of the off-the-shelf oils to break it in or run it after break in... he informed me that the API (American Petroleum Institute) changed standards about a year ago that reduced the zinc and phosphorus content by half in order to extend the life of the catalytic converters in newer cars (and didn't tell anyone about it!), and since the newer cars all run roller cams or over-head cams, the wear isn't a problem with these cars... now, I thought the guy was just trying to be slick (pun intended) to upsell me on some exorbitantly priced oil because he knew he had me by the short and curlies... so I shelled (another pun) out another $150 for 5qts of break-in oil and a case of 15w-50... when I got home, I fired up the old internet and started researching it... turns out, the guy was right (I figured he probably was, he runs a reputable machine shop here in "the Springs")... in the past 12-18 months engine builders have been seeing an alarming rate of camshaft failure due to the low zinc and phosphorous content in the new API standard oils... the engines most at risk are older flat-tappet (hydraulic and solid) cam motors with a valve lift beyond stock or a rev range beyond stock... basically any pre-2000, high performance push-rod motor... which, I assume, most folks on this site likely own... so, just a heads up... here's a link to a decent article on the topic (doh! ... you'll have to search for it, I'm not allowed to post URLs here yet because I'm new

)... enjoy, and happy wheeling!
... the site is called enginebuildermag dot com... the story is called "Performance oils and additives: Got Zinc?"...
by the way... the oil I bought was called "Joe Gibbs" racing oil... another decent oil seems to be something called "Brad Penn"... both available at retailers in C.S. and Denver