Flattened a leaf.

To the OP. I'm guessing your 5 year old springs were just worn out and gave up with the first full throttle under the new found power.

I ran SS springs for 5 years on my Dart. First 2 years with a gutless 318, next three years with a 400 horse magnum and lots of track time.

One day I walk out and the passenger side spring had given up. Dropped about 3 inches. Ordered brand new SS springs from summit and haven't had any problems yet. They lasted me through drag week so I'm thinking they are good. Also making much more power now because I procharged the magnum