What is the absolute minimum clearance that I can get away with on a valve spring? Cast iron Indy heads, .650" lift Comp cam, BUT with 1.6 ratio rockers makes it .693 valve lift. Spring specs says 1.175" coil bind (going to check it tomorrow to see what it actually binds at).
My math says 1.175"(coil bind) plus .693"(gross lift) minus .028"(valve lash) equals 1.840" installed height. How much more do I need for MINIMUM clearance? Or another way to ask this, how little can I get away with? I now have 1.877", I'm thinking that ain't enough. (541 ci RB, solid lift cam, 2 speed racing transmission)

Thanks, Brian

Call the valve spring company or the cam company you got those springs from and ask them this question I use .060 to .080 from coil bind on all of my roller cam valve springs On the others type camshafts if it is within .100 of coil bind and has at least the pressures the cam company wants I call that good I will add from 40 to 60 lbs pressures on the seats and try to keep the open pressures to no more than 375 lbs or less on flat tappet bracket cams

I would suggest not solid stacking the springs. I would mockup with some light springs & see what open height you get then compress one of your springs in a vise & see what develops for clearance as you approach that dimention. if you have at least .010" between 6 coils (.060" or more) as you get to the dimention I think you are OK. I'd wanna know the PSI at that open dimention also. special retainers can alter the height (& psi also)

Add +.050" retainers or locks. Or cut the spring pockets .020". .050" should be plenty.
Doug

All that easy enough to figure --the deal with Indy iron heads ( big block)..and it is crucial..You must have pretty sloppy valve to guide clearance--otherwise the valve will hang in the guide on the two center exh valves--those heads retain so much heat there it can happen easily Indy always fails to mention this little fact. Also of great importance is the fact that they are thin behind the quench part of the chamber--you can't mill them much at all or that area of the chamber can/will collapse
They may have fixed this from last time I had any but I would doubt it and..you may have older castings. my two cents worth--hey..they will make great power just take care on the guides I have even run them with no exh seals

Cutting the spring pockets would be the best solution, however the intake ports are VERY thin at one point (between the spring pocket and intake port), and makes me nervous about taking another .020" from there. I do not want to break through the port. Also, a taller retainer could be an option, but the rockers have already had to be clearanced to keep from hitting the retainers. Could shim up the shafts I guess.
Exhaust seats are not a problem at all, plenty of meat there.
And yes, these heads are very thin over the combustion chambers. We also run the valve guides loose.
Any other options?

Thanks,
Brian

Odd thing is we had a very early set of these in the mid 90's. We milled them .100" to get the compression up on Indy's recommendation. Later talking to Indy they said don't mill them very much or you'll ruin them. We ran them about 5 years before going to aluminum. Never had an issue.
Doug