Cdog
If your are using the .647 lift solid cam as comes standard in the 514 crate from Ford Racing, I have seen several failures with this cam, including my own. In my case it was inner valve springs that broke(6 at 5000 miles), but other's I know of have broke both springs and rollers in as low as 1000 miles.
The problem is that this cam has an extremely fast ramp on it. It’s great for drag racing as it was intended, but in street use where you are not constantly on top of adjustment and hardware condition, the slightest irregularity can lead to failure.
Personally, I have switched to the to CompCams hydraulic flat tappet 34-337-4
http://www.compcams.com/catalog/178_179.html#Anchor . The lift on this cam is only .585 and of course the ramp is slower to accommodate the flat tappet, but on chassis dyno runs and street shoot-outs, I have found it to be able to match any and faster than some. And of course, this configuration is pretty much bullet proof.
Craig