Hey everybody! Guess what! I just got done rebuilding my 350 v8 for my 75 El Camino. I put some double hump heads on it, and they do not have hardened valve seats. I intend to drive this car almost daily. Should I run leaded fuel additive, or a little bit of diesel in my fuel, or what? Is there a good study on it? I've read about it on other forums, and nobody really came up with a definitive conclusion. I always run 91 octane, usually with no ethanol. This is a high compression engine. I read about the rash of head jobs back in the 70s, and something about ultra lean fuel tuning for the emissions tests having something to do with it.