What is accepted tolerance for new aftermarket valve springs?

yellow rose said
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.

Thanks for reply, and no I am not a journalist. I see the spring rate values given but I am not sure how to test that. It would have been nice if these Comp springs WERE 5-10% over as you say, but they are all under (except one, which was way over at 347#). It would be interesting to see the values after they had been run in an engine for a few hours. But I don't have that luxury. I will contact Comp and see what they say about it. But I don't expect much interest from them.