The Law mentioned Texaco gas above and that got me wondering. I live in a rural area and the choice of gas normally is Texaco and No Name.Anyway a couple weeks ago I had to pull a loaded horse trailer over a mountain pass 2 days in a row. This is about 1 1/2 miles of 6% grade going from 3000' to 3800'. One of the places where I ping with a load. So the first day I had Texaco Premium with the usual ping, the second day I had Union 76 Premium with no ping. Weather , temperature, time of day, etc. were all the same. And here I thought I was doing good by running a name brand gas. By the way, I do have C9 heads for 9.4 compression and headers. What I have done since then is put a valve on the timing vacuum advance line and mounted it by the trailer brake control. When I come to a long grade I turn the vacuum advance off, which takes away 10-15 degrees of overall advance and there is no pinging. this is cheap, easy , and on demand so you dont have to run in a perpetual de-tuned mode. Also this should work when I drop down to sea level once a year from 3000' where I live.