I have a 1975 chevrolet 454 Barth. Does anyone use the lead substitute additive for these older engines? I have been told that the lead was used for valve guide lubrication.

Back in the good old days, the lead compounds were added to increase the octane rating, allowing the refiners to run more lower octane product and boost it with the additives.

Being metallic, the lead burns to a solid ash residue, some of which ended up fouling the plugs, etc, the rest went out the exhaust and coated the valve seats (and ditches) with lead residue. The up side was that the residue provided a cushion for the valve as it closed on the seat, reducing valve seat wear.

When they finally got the lead out, the car companies were slow to modify the engines and many early no lead engines had premature valve wear due to the soft seats.

BTW, they put "Stellite" hardened valve seats in aircraft and marine engines for years before that and for probably 12 cents per car they could have done the car engines, too...

After about 1976 they put hardened seats in almost all engines.

So, back to the point.... your engine might be old enough to have the old style seats. Check the VIN exactly with a good GM guy and they can tell you.

If it does have the old seats and compression is good, run it. It may last quite a while.

If the valves are leaking, then get a valve job done and new seats installed at that time. Good to go.

I have no experience with the lead substitute additives, I'm afraid many are snake oil. Some are OK at increasing octane but I don't know if they help the valve problem. TCP is a popular one.

Thank you Steve, that is the most complete explanation I have received.

Iam

Steve's description is almost complete. (I'm a recovering fuels and lube engineer). Most companies formulated with a scavenging compound, something like tricresyl phosphate (TCP), which pretty much lessened lead deposits. TCP also had the advantage of cushioning valve seats in the days of low-lead gaso.

But as Steve mentioned, the standard valve seats were subject to excessive wear with unleaded gaso, and this was worsened with valve rotators. Recall that trucks weren't required to run unleaded until a few years after cars were.

I suspect that most of these contain a cheap oil and some phosphate or sulfate compound. Note that all seem to specify the product is for "off-road" or "marine" use, a red flag IMHO. I've not been able to locate a MSDS on any of them.

Anyway, I'd avoid them and just run unleaded; like Steve mentioned, most are likely snake oil (the industry technical term is "mouse milk"). Excessive wear is a possibility, not a probability.