RE: My new buggy!
There is a thin metal gasket/shim between the cylinder sleeve and the head button. Some engines require an extra shim to be placed under the head button to run higher nitro content fuels. Adding a shim reduces compression by adding volume to the combustion chamber which in turn lowers cylinder pressure and retards the ignition timing. In the case of high nitro content fuels this reduces the chance of detonation which is the fuel igniting before it is supposed to. Whatever power lost to reduced compression is made up by the higher nitro content in the fuel.
Turbo heads require turbo plugs. When installed they have a combustion chanber shape that is supposed to be more efficient and produce more power This is because the plug doesn't sit into the chamber obstructing the burn and flow like a standard plug. Instead it sits flush and helps form a smooth rounded shape in the chamber to help improve the burn and flow. Thats the theory, I've never tried to prove or disprove it. In my experience turbo plugs did seem to last slightly longer though.
Edit: JohnP2 good call on the ignition timing, I missed that totally. And at first I thought you were referring to port timing, either way I had to edit my post.