The quality of gasoline here in AZ is abysmal, my previous engine was 9:1 compression and i wasted lots of time and money trying to make it run perfect. I had the best mechanical pump you could buy and had vapor lock issues. switched to an electric pump and return system and still had issues. I completely emptied my system and filled with AV gasoline and no more problems, the engine idled much smoother and ran way better. Since then the only thing that goes in my tank is race gas or AV gas. I don't care how much it cost, just want my engine to run good. The other problem with today's gasoline with the corn juice is if you let the car sit for any length of time it really messes with the carburetor. Also change all the rubber fuel lines in your car. Lead or no lead is really a moot point with a hydraulic tappet cam that only has 100-120 lbs seat pressure. Never seen any adverse effects on any cylinder heads i have worked on.