Mmmmmm... well I ran 8.2-8.3 DCR on the street years ago with iron heads and quench and premium fuel... ran over 90k miles that way. I di have to be careful with ignition timing. A 7.5:1 DCR limit is way to low and unnecessarily limiting in my view. Use quench and small combustion chambers and don't fear going into the low 8's with iron heads....IMHO.
