It is a combination of things actually. How much engine do you know?
Are you the builder?
When you did the piston to valve clearance test, what kind of numbers did you come up with? How did you determine you have 11:1 right now?
Flycutting the tops is for valve clearance and, if done too much, will weaken the top of the piston allowing a hole to be punched in it with any number of anomolies.
New pistons, the openning of combustion chambers and special head gaskets can be used to reduce the compression ratio.
The amount of material on top of the piston is probably not enough to allow a you to "just drop in a crank". Then there is the deck. How high is the deck?
The list goes on.
Hope this helps.
