Unleaded gas or use a lead additive for new engine

Thanks,

scott#2

Short answer - Run straight unleaded.

Long answer - Detonation has been a problem since gasoline engines first appeared. A spark would start the combustion process in a controlled fashion, but some of the fuel would start to decompose before the flamefront within the cylinder would reach it. A byproduct of the decomposition would be compounds that could burn without a spark. These are called auto-ignition compounds, and their presence would eventually result in an uncontrolled, and over-rapid burning of the remaining air and fuel mixture which we recognize as detonation. Working backwards, we can see that the decomposition is caused by the heat of compression before the spark, the residual heat in the cylinder and heads, and the heat produced by the ignition of the fuel itself. Several chemicals were tried in an effort to eliminate detonation. Aniline, iodine, selenium oxychloride, methylclopentadienyl manganese tricarbonly, and a list that goes on and on. Finally, in the 1920's, it was noticed that certain lead products had a very high natural knock resistance. Soon, tetra-ethyl lead was used as an easy way to increase the octane numbers, which allowed higher compressions, and as a result, more power output. A side benefit of using lead was that, after the lead was involved in the burning process, a lead oxide then coated the valve seating area. This helped to stop the valve seat recession which was another problem of the time when using the cast iron heads. The early engines also had no valve seals, and the oil would drip down the valve stem. This caused a little bit of smoke, but it lubricated the valve stem where it contacted the cast iron head. When valve seals came into use, the lead became more important for a small amount of lubrication between the valves and the head. Lead was here to stay, at least for a while. One of the drawbacks of using the lead though, was that it would tend to build up on the insides of the engines. To reduce this, ethylene dibromide and ethylene dichloride were added to act as scavengers and keep the engines cleaner. Anyway, this explains why the lead used to be there. Today, newer engines, and rebuilt engines, use hardened valve seats and alloy valve guides that do not require leaded fuels for valve guide lubrication. How the octane numbers have been increased without the lead is a whole different thread.

John In Iowa

In addition to the anti knock properties afforded by "leaded" gas another benefit was how it softened/lubricated the valve face to valve seat impact to reduce wear and recission of the valve down into the seat plus it reduced sticking. One way to counteract that if you werent gonna use leaded gas was to use hardened valves and/or seats (if used in that engine) and I dont know if your rebuild involved that or not?????

Buttttt t regardless unless youre gonan run that engine longgggg g n hottttt ttt n harddddd dd for extended periods, Id say it will take a longgggg ggg time to wear the new valves n seats so bad it would be a problem and you could counteract that to some extent by checking n adjusting the valve lash time to time if ever needed.

Sooooo ooooo not knowing what, IF ANY, help any snake oil or so called lead substitute could provide in the long haul I think Id do without it especially if you used hardened valves/seats in the overhaul. I just dont forsee any additive making all that much difference in valve wear and unless you really raised the compression drastically I sure dont see preignition or spark knock as any problem that would require the use of higher octane gasoline or any ant knock additive such as a lead substitute.

I reckon I agree with the other gents SAVE YOUR MONEY

John T