[cnavarro]

It partially has to do with what deck height was used when designing the piston.

To give you an example, a 93mm 2.9 10.5:1 piston at a .040" deck requires a 24.6cc dome (assuming a 68cc head). If you take that same piston to a .060" deck, the same piston becomes a 9.9:1 piston.

So, the statement that running a .040" deck lowers the potential of detonation is assuming that at that tight of a deck you aren't exceeding the octane requirements allowed (before requiring twin plugging and/or race fuel). That said, there are a lot of builders who set their engines up for .060" deck and I design the pistons as such to increase the dome volume to ensure they are still netting their target compression ratios. As long as you stay within the realm of .040-.060" deck, you're totally fine.