What is accepted tolerance for new aftermarket valve springs?

When you get into the better springs...they are usually between 5 and 10 percent higher than the spring is called out for. This compensates for pressure loss when the springs go through their first few heat cycles.


For what you are testing I wouldn't worry about it. Shim a bit if have to. I've never really been concerned about the pressures as much as I am the spring rate. What I've found is the cheap springs don't have the spring rate they should. IOW, if you are 5% down on installed height and open pressure is the spring rate what they should be. If not, get new springs. If the rate is correct then shim them a bit and go.