What thickness does the combustion chamber require in motorcycle engine head design?

Hello all. I am trying to design an engine head for a single-cylinder motorcycle with a capacity of more than 350 cc. What is the thickness that can be taken inside the combustion chamber from the side of the engine head? I found examples that use a thickness of 7 mm and others that rely on 6 mm... Is this thickness sufficient in practice? Waiting for the news, thank you very much.