When comparing a roller cam with a flat tappet cam, consider this: Because of the design of the roller lifters, the cam lobes on a roller cam can be ground with more aggressive ramps which results in the valves opening quicker. This quickness allows flow to begin earlier and continue longer without having to resort to a longer duration cam to get the same flow. So basically you get more flow with the same .050 duration and we all know how important flow is.
If the same lobes were ground on a flat tappet cam, the edge of the flat tappet lifters would dig into the cam's lobes which will cause instant failure.
As with most things, there are pluses and minuses. Roller cams and lifters are more expensive, especially if the block you're using isn't one designed from the factory to run a roller cam. In cases like that, you'd need a roller cam retro-fit kit and by the time you buy all the parts you'd need, you'll be closing in on $1,000 - cam, lifters, springs, thrust button, Torrington bearing, guide plates and, because roller lifters are taller, shorter, hardened pushrods.
A problem that has surfaced with flat tappet cams is their frequent failure. The research into this shows that the failures are thought to be caused by a change in the formula of the engine oil. An additive package that use to be in dino oil has been dramatically reduced and, as a result, more flat tappet cam failures are occurring. Corvette Action Center's site has a very detailed investigative report on this issue.
Many guys still run flat tappet cams and many race sanctioning bodies don't allow roller cams, but roller cams are at the cutting edge in cam development. Many factory performance engines, like Corvettes, have been coming from the factory with roller cams since 1987.
If your budget can handle it, a roller cam is the way to go. Deciding on which specs to choose in the new roller cam is another can of worms altogether.
Jake
West Point ROCKS!
