Let me try to make this short...I bought my car, the tank was near empty, I filled it up with regular 87 octane gas. It started pinging so I retarded the timing from 13 to about 7 before it stopped pinging. I ran a few tanks of high octane through it before I advanced my timing back up to 10. My bottom end power is great,I can floor it and get no pinging. But when Im on the highway and punch it, I get a lot of pinging. It never pinged when I test drove it, however I never drove it on the highway. I hate to retard my timing more than I have to, but unless I can get some suggestions from you all Im going to have to. My engine is a 383, Holly carb, 700r4 tranny. I dont know if you need any other info? Your help is appreciated!