Putting together a 340 for my son's car and thinking about running the .508 purple shaft cam. What valve spring should I run with this setup? Heads currently have the single with a damper.

When I ran a 340 & liked to pedal it spiritedly, i found the stock springs were kinda too soft for the stock style valve. After a couple of changes I found Comp Cams 920 spring, installed @ 1.7 worked great & didn't hammer the lock area of the valve. The std valve is heavy, look for lite weight valves & drive it like you stole it.

Watch the guide/seal to retainer clearance......Might want to check that first.