Was at the track a couple days ago when my motor made horrible noises at rev limiter. Pulled the motor out and took the head off to inspect. One exhaust valve broke entirely and bent all the rest in the same cylinder (#1) for obvious reasons. I am very unsure what happened, I suspect valve float? Rev limiter is set to 7800. 10 events on a fresh rebuild, standard engine besides arp head studs, arp rod bolts, ACL race bearings, and cometic head gasket. It was running fantastic and rock solid all year. The valve spring, keeper, and retainer were all in perfect shape. I find it curious though that the valve stem was not bent, almost like it did not contact the piston at the time of breaking. Timing was dead on, and car was dyno tuned by a very good tuner at 412hp. Any ideas? would like to prevent this on the new motor.