440 Source Aluminum Big Block Heads

Has anybody out there had any problems with these heads? I put a set on my car this year with good and bad results. The motor is, was a 383 with 12.5:1 compression, .590/312 purple shaft cam, edelbrock victor intake. All I did to the heads was change the springs and opened up the pushrod holes. The car ran great all season both on and off the track. Last month I was at the track and on the fifth pass I had a valve break and it toasted the motor. Anybody else have problems?