unleaded gas in cars designed for leaded gas

[Michael Schweitzer]

I did a five year search and didn't see the same question, but excuse me if this has been answered before. I've long heard that leaded gasoline contained lead because engines from that period 160's and earlier were "softer" and needed the lead in order to not have increased cylinder head and piston wear.

If this is the case, does anyone suggest putting lead additives in unleaded gas for mid sixties cars?

[Joe L.]

Re: unleaded gas in cars designed for leaded gas

Michael-----

You don't really need it. The main problem for using unleaded gas in engines designed for leaded involves the POSSIBILITY of increased exhaust valve seat wear. This is RARELY a problem, though.

By the way, OVERALL unleaded gas is FAR better for an engine than leaded. Leaded gas is good for exhaust valve seats and BAD for just about everything else. You're much better off with unleaded gas. Especially, since you don't really need the exhaust valve seat protection, anyway.

[Michael M.]

Re: unleaded gas in cars designed for leaded gas

Joe, don't you need to install hardened valve seats to obviate the need for lead or a lead additive? Otherwise, I think the engine may be prone to valve seat wear.

[Duke W.]

Re: unleaded gas in cars designed for leaded gas

GM published a paper in the seventies that reported higher valve seat recession for unleaded fuel in medium duty truck service, and the myth just won't die.

For passenger cars valve seat recession is rarely an issue since they operate at much lower average load.

It's far more important to keep the valves lashed properly, especially on mechanical lifter cams and the OE clearance specs are too loose, so the valves get slammed into the seat pretty hard, which can contribute to seat recession.

There have been reports of seat inserts coming loose on rebuilt engines. Unless you are building a racing or heavy towing engine the cost and risk is not worth the potential benefits.

TEL does provide some benefits to seats, and if a few tanks of leaded fuel are used early in the engine's life, the beneficial effects will last for tens of thousands of miles. The benefits of TEL on valveseats are realized at very low TEL concentration, so mixing in a 25 percent blend of 100LL avgas or race gas is all you need to do to get the benefit.

Duke

[Michael W.]

Re: unleaded gas in cars designed for leaded gas

That's another internet legend that's existed even before there was an internet. Exhaust valves on Corvette engines don't run hot enough to risk the microwelding that leads to valve recession. See Duke's response below.

[mike cobine]

Re: unleaded gas in cars designed for leaded gas

Duke has already touched on why this myth exists. Machine shop operators I knew in the early '80s told me that the wear could be 10% to 20% increase in valve seat wear. Remember that these guys were basically reporting on engines run hard, drag raced, etc. The normal driving Mom or Pop didn't pull their heads and take them into performance machine shops for valve jobs.

Basically, that boils down to if you needed a valve job at 100,000 miles with leaded gas, you probably need on between 80,000 and 90,000 miles with unleaded.

How far are you planning on driving that Corvette of yours? Many Corvettes have never hit 90,000 miles in their 30 or 40 years of life.

Machine shop operators I've known over the last 15 years have said they have definitely seen hardened seat inserts drop. The result isn't pretty. If the shop putting them in doesn't do it right, you will have a problem - a big one.