hey, ive been using ac delco R45TS gapped at .045... 350sbc... im at about 10.7:1 CR bored .060 over... have to run 94 octane or better or it runs like TRASH. They seem to last a decent bit but i like to change them about once every 2-3 months... I've also learned if you let the car warm up properly *living in a cooler climate anyhow* then the plugs should last a bit longer.... but myabe its all in my head