[scuncio]

The Felpro multilayer coated gaskets (standard blue ones) are typically around 0.041" compressed thickness. If memory serves me right the original steel shim gaskets are closer to 0.019" compressed thickness. Combine that with the typical 0.015" piston depth below the deck (assuming a factory piston and a factory deck surface), it's almost guaranteed that you'll have a lower CR than advertised. For example, my stock 1970 LS5 ended up being around 9.75:1 with the 0.041" Felpro gasket and stock pistons that were 0.016" below the deck. Just my experience.