Valve spring coil bind question?

[Al Weyman]

I have been checking the coil spring clearance on a new engine I am building with a .645" inlet valve lift with 1.5 rockers (quite a stout roller cam). The springs are well up to the job with titanium retainers so I am not expecting any float however searching the net its obvious some people are getting their lines crossed with how much clearance you should have before the spring goes close to bound. On the Iskaderian site for example they say as long as you can get 10 thou feeler between the coils with the valve fully open which if stacked up would give a total of 60thou clearance then you are OK others seem to think its 60 thou between coils.

Can anyone throw any light on this as I have calulated I have about 100 thou before it binds but can only get a 25 thou feeler between the coils. I feel this is about right especially with the very stout springs and light titanium retainers but would appreciate an opinion.