So apparently I've been running with three broken valve springs -- for several hundred miles! The weird thing is that the car drove fine. I haven't had it on the track for about 9 months so the only time I noticed something was up was when I did a blast down the street and it fell on it's face at about 6200RPM instead of running up to 7k like it used to.

I took it apart and found three of them snapped very clean. No trace of metal fragments or other damage. They're comp 953 double springs with dampers. Definitely not coil bind and they're not that old -- 5 years and maybe 10K miles max, although the motor does have about 10 hours of road race time on it, spread over those years. The only thing I can think of is either they were bad to begin with, or my cam's profile was too much for them (230/236@.05", .624" valve lift). AFR 201 eliminators with T&D 1.6 shaft rockers.

I'm going to swap out the valve seals and check the guides while I have them apart.

Now the trick is what springs to replace them with....
Any thoughts?

 

I would look at the AFR valve springs at Summit Racing.