At 10:54 AM 7/6/2004, you wrote:
I guy asked me what fuel I used in my '66 Chevelle (stock 396 with mild cam) while we were waiting for our step off time in the local July 4th Parade. I told him regular 89 octane right now, but have used 91 and 93 octane and noticed now real difference in how the car ran. He got all over me for not using a "lead additive". I told him I am under the theory that the engine has been heated up and cold down so many times over the years that the valve guides are hardened by now (I do plan on rebuilding the engine with hardened guides in a few years when doing my restoration). His point was that without having a lead additive that damage would be caused to the pistons by blowing holes in them if the car back fires or pings especially under hard acceleration. My hardly occasional back fire comes through my carb and the car is timed that it never ping's. I do get an occasional engine run on for a half a second which I could blame on the lower octane. Any one using "lead additive" and any thoughts supporting this guys comments?
The guides aren't the problem, it's the valve seats, esp the exhaust seats. You're only going to blow holes in the pistons under REALLY hard detonation, and since the car doesn't ping, you aren't having that problem. I don't know what a backfire would have to do with anything (???). If the motor has a lot of miles on it running unleaded fuel, you'll probably see some sinking of the exhaust valves when you pull the heads off. The lead acts as a lubricant for the valve seats, and without it, the valve wears away the seat and starts to sink. The hardened seats are made of a different (harder) material so that they don't need the lead. Heat cycles have nothing to do with making the seats any harder or softer. Adding the additive now may not help if the seats are already worn, but it sure wouldn't hurt to use it to prevent any further wear.
BL
