Charlie's information pertained to the quench space between the cylinder head deck and the engine block deck OR the dimension between the piston at T.D.C. and the deck of the cylinder head . As Charlie stated, too large a cylinder head quench space can result in ignition detonation problems. The exact dimension of when that detonation situation may occur can vary with geographic location (altitude above sea level), atmospheric conditions (temperature and humidity), and the engine's normal operating temperature (cooling system condition, engine compartment ventilation factors, etc.).
Quench space dimension is a combination of piston top distance below the engine block deck and the thickness of the compressed cylinder head gasket you choose to use.
What causes some of us problems is rebuilding a FoMoCo machined y-block that likely came off the production line with the FoMoCo pistons .025 in the hole (below the block deck surface at TDC). In servicing the engine, if aftermarket replacement pistons are used (SilvOLite or Sealed Power as examples), according to the box they were supplied in, the replacement pistons were manufactured with a compression distance (center of piston pin to piston top) that is .020 less than the FoMoCo original piston! Therefore, the new quench dimension without considering the compressed thickness of the cylinder head gasket to be used is already likely .045 inch.
After you look at what the head gasket adds to that quench dimension, you may have a total quench space figure that is not good for operating your rebuilt engine where you drive your vehicle. Think of your vehicle operating in the Southwestern states on a summer day . . . Or your vehicle operating in a 4th of July parade.
Ted Eaton generated a chart that will help you to determine how many ccs to add to the volume of the combustion chambers your cylinder heads have (this will lower the static compression ratio of your cylinder heads) and how much compressed gasket thickness to add to the quench space dimension you have with your piston in-the-hole dimension.
Ted Eaton's web page info will supply you with the two information items mentioned above. Click the link below . . .
http://www.eatonbalancing.com/2012/06/30/head-gasket-volume-calculation/John Mummert's web page will supply you with the cc volume for many of the y-block heads you might be using. Click the link below . . .
http://ford-y-block.com/cylinderheadchart.htm Kultulz's comment regarding aluminum heads on cast iron blocks raises another discussion. Yes, aluminum and cast iron expand at very different rates. Using a steel gasket between an aluminum cylinder head and a cast iron block may also raise the concern of electrolysis taking place between the two different metals.
IMO, having your y-block engine block squared and zero decked is important to seriously consider doing to maintain original engine performance as you use over-the-counter replacement pistons and today's preferred composite cylinder head gaskets in your engine rebuild undertaking.
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York