It's not the valves but the valve seats, in the cylinder head, which are hardened using an alloy of cobalt, chromium, tungsten, molybdenum and iron, called Stellite. Without the lubricating properties of lead in gasoline, it was found in certain types of severe service that the valve seats would malform.
So Stellite will prevent this from happening. Obviously, you are not going to be able to buy a lead additive for your fuel.
I think you just buy hardened seats and have them installed by a machine shop but Shifty can answer that better. You can't buy lead additive but as I recall you can buy lead substitute.
My suggestion would be to see if there are any '71-up heads that will work on the cars you like. 1971 is the year they made engines compatible with unleaded and lowered compression ratios. These heads not only have the hardened seats but (sometimes) larger chambers that give a compression ratio that tolerates 91 octane.
This isn't always an option--I don't know if '71+ Cadillac heads will bolt to a '62 390 block, for example, although they probably will--but it kills two birds with one stone.
Later heads are a straightforward swap with the GTO and Mustang you've been talking about. With the '62 Cad it gets a little complicated. You'd want a machine shop to check valve-to-piston clearance, and make sure the large chamber 472-500 heads don't give you a 6:1 compression ratio with the 390's smaller cylinders. And there'd be a port mismatch but I don't think that's a big deal.
On second thought, just yank that puny 390 and bolt in an Eldorado 500.
While the link below is from a Pontiac-oriented website, it is germane to the most recent posts in this discussion forum. This link is for a detailed article that discusses the chemical composition of modern gasoline, engine compression ratios, the subject of gasoline additives and how well they actually work.
This article may raise more questions than it answers, but it appears to be a pretty good technical reference source.
That's an interesting article. He seems to know a lot more about this than I do but I'll throw in my two cents worth anyway.
He defines knocking as uncontrolled combustion *after* the spark plug fires. My understanding is that "pinging" can also come from "pre-ignition" which is uncontrolled combustion *before* the plug sparks. With pre-ignition you've got combustion pressure trying to drive the piston down as if it was on its power stroke when in fact the piston is on its way up on the compression stroke. This shortens the life of the reciprocating parts considerably.
He also talks about the advertised or nominal compression ratio usually being higher than the actual CR. Some engines came with two head gaskets--take one out and you've got a higher CR. Because of manufacturing variances, combustion chambers in the same head usually aren't all the same size. This means you can have a small chamber that starts to knock before the others do because that cylinder has the highest actual compression ratio. You can "cc" the heads to make sure the chambers are all the same size.
He also talks about "lazy" ignition timing in '70s engines, something I had also mentioned (great minds thinking alike). I wish he had talked more about how productive it can be to recurve the advance and crank in more initial advance. That has a huge effect on combustion pressure and you can use it to compensate for a compression ratio that's too low or too high.
He also talks a little about some of the other factors that influence knocking. He doesn't go into much detail so I'll try to fill in some of the blanks.
air temperature (both ambient and underhood)--the hotter the temp the more prone to knocking the engine will be. And of course it's even hotter under the hood. Most factory "ram air" packages were actually cold air packages, since the scoop was usually placed in a location with little ram effect.
head temp--how well the engine cooling system cools the combustion chamber. He also doesn't mention how cylinder head design (hemi or wedge, open or closed chamber) has a big effect on knocking.
load--lugging an engine increases its tendency to knock, but where this really shows up is in cars with freeway gears (ratios less than 3:1).
spark plugs--have different heat ranges. A colder plug lessens the tendency to knock, but a plug that's too cold will foul ("load up") with carbon and quit firing.
I also wish he had talked about water injection. Most people think this is just a gimmick but I understand they used it on WWII fighter engines.
#163 of 184 Speedshift: Octagane was the name of the water injector
Jan 12, 2002 (5:03 pm)
used in my father's '50 Cadillac Series 61 Sedan. It had 331 c.i.OHV V8, 7.5/1 compression ratio and water injection. I remember he could never get it adjusted just right, but the engine could be started when the battery was dead under compression as the Hydramatic had 4 speeds then. Roll it over 35 and drop it into "L". Was it Charles F. Kettering who designed the transmission? He is considered to have authored the Rocket 88 and the Cad V8 in '49.