Fuel octane on hp 273charger engine 10.5:1 compression .

The compression numbers are good. Sounds like a healthy mill. Like the others said, use 93 octane, don't crowd the timing, and watch for ping. Demon416 suggested lead additive which is a good idea too. When I rebuilt my Charger 273
the Egge HP pistons were a little over 9:1. I milled the heads a bit and got to 9.6 with a thin head gasket.. 93 octane and no ping with around 15* initial timing. I had a talk with the shop that did my heads and they don't like hardened seats in old heads. I only put a couple thousand miles a year on my car so the standard valves and seats should last for many years without lead additive. tmm