Originally Posted by TX512
interesting. can you elaborate... thanks
The OEMs switched to roller cams in the mid 1980's because the EPA wanted ZDDP (Zinc Dialkyl Dithio Phosphate) out of oil because it contaminates catalytic converters making them less efficient across time.
The manufacturers understood from their own long term reliability analysis projects that ZDDP is a very useful chemical in oil. It provides what engineers call Boundary Lubrication. It does this by embedding itself into the pores and forms a layer a couple molecules deep on the metals it contacts. If your old enough to remember the TEXACO ads of 40 years ago where they drove a NYC taxi around Manhattan for a day with no oil in it, that's how tough this stuff is.
In our particular case of flat tappet cams, in modern OHV engines the forces are much greater on the valve train parts than the old flat heads. It was found in automotive engines of the 1950s, as it was in WW II aircraft engines, that as loading and speed on these parts went up, so did wear when additive free oil was used. This is because the interface of lobe and lifter doesn't form a wedge of oil between them like shaft journals and bearings do. So part life expectancy in modern engines became tied to ZDDP. Other chemistry has been tried such as Molybdenum Disulfide. It's great stuff and will fill many of the same purposes as ZDDP. But there's a Catch 22. Moly just loves itself, you can grind this stuff into the finest powder possible, mix it with oil and pour it into your engine. But, each molecule immediately starts hunting other molecules just like it. They start to gang up with each other and before you know it, the gang is big enough to get caught in the oil filters drag net. So little by little and faster and faster it goes away.
The OEMs realizing there was no inexpensive option to keeping warranty claims to a minimum all went to roller cams. The hidden lesson here is that of all the better materials cams and lifters could be made from, of all the high-tech processes that could be brought to bear against the problem, the most cost effective solution was to go roller. That says a lot about the problem.
So getting to my recommendation of going with the Vortec block is that we today have a very high failure rate with flat tappet cams, it doesn't take a lot of nosing around in this form to discover that. The additional benefit is that the Vortec block can be run with a flat tappet cam or a OEM roller. A factory roller is lot less expensive to but into a factory roller prepped block than an aftermarket roller into a flat tappet block. The flat tappet block does not accept a factory roller conversion without a lot of effort and expense and is hardly worth attempting against the cost of an aftermarket roller. I mean its done but in the end you save a hundred bucks or less and own a what is often a kludged mix of parts that doesn't function well.
There are many ZDDP additives sold in the aftermarket, so far none seem to have the long term qualities that used to be found in the oil formulations of the major petrol companies. I suspect that from a chemistry stand point, that there's something else missing that was used to enhance, correct, or control ZDDP that the big oil company's either kept proprietary or there is another chemical the EPA had removed that performed the functions I sighted.