Couple weeks ago "2 Guys Garage" had a Comp Cams tech on there show...even he said as good as they can be, there's just to many moving parts that can go wrong with Rollers...then he stated that Winston Cup cars use Flat lifters that are spining to almost 9000 rpm...guess the Winston Cup Cars don't want to chance a roller failure during a race...guess the few Ponys lost is worth it.