tomporch

Should I be using a lead additive in my 1969 390hp big block?

MelWff

Unless you are doing something that is considered severe service, towing a trailer up a mountain, it is not needed. You should be using the highest pump octane gas you can find.

Mike Ward

No street driven Corvette requires leaded fuel.

jb78L-82

If you have a pre 1971 cylinder head without the hardened valve seats that GM began using in their engines that year, leaded gasoline is need for lubrication of the valve seat. A lead substitue should be used to prevent premature valve issues....

http://www.gm.com/company/historyAnd...evolution.html

Most sources state that high performance driving with the non hardened valve seats is NOT recommmended without lead or lead subsitute in the gas.

Mike Ward

No Corvette engine is loaded hard enough for long enough to create the conditions that result in valve seat recession.

Melwff is right.

tomporch

Thank you for the information

tomporch

Appreciate the response. I see there are varying opinions on this subject.
Sounds like it wouldn't hurt it to run a little lead but probably not necessary with casual pleasure driving around town.

Paul L

I have driven a 1967, 1974, and 1979 on unleaded fuel for many miles with no problems.

Mike Ward

Suit yourself but very, very few additives actually contain any lead. TEL for street use has been illegal for many years..............

jb78L-82

http://www.gm.com/company/historyAnd...evolution.html

jb78L-82

As stated earlier, most pre 71 engines will have no issues with valve seats and unleaded gas as long as the engine is not highly stressed even though said engines were designed for leaded gasoline….Also, as stated earlier you do not need to use lead additives but can also use lead substitute additives, if one wants to be prudent with a pre 71 GM engine.

Mike Ward

And forty+ years of experience have taught us that these precautions were not warranted except in rare circumstance, none of which are applicable to Corvettes....

Let's stop perpetuating an old story.

Roughrider

Amoco was blending and selling unleaded gasoline since at least the early 1960's, if not earlier. I don't remember hearing of any problems blamed on unleaded fuel until it was mandated by the government in the 1970's.

I think a lot of engine problems that were blamed on unleaded gasoline were engines that were worn, under maintained and blaming it on the fuel was a convenient excuse.

Mike Ward

Exactly.

Fast forward to today and we blame the same problems on ethanol. It's like a deja vu all over again.

Paul L

Mike,

Yes and no. Unless you use Viton components in Q-Jets, the original rubber parts can turn to mush via ethanol. I have experienced that. And it is well documented by Lars.

TedH

Purely as an aside, my DART Iron Eagles with 'hardened seats' lasted 30k miles. After valve guide wear and recessed seats, I installed new bronze guides and steel (iron?) valve seats. Valves were clean but the darn umbrella seals failed completely on some exhaust valves.

This was running 92 octane and 30k of occasional Sunday drives. Some spirited driving thrown in for good measure...

I would expect the same results running a 1970 cast iron head on unleaded for 30k miles over the course of 14 years.

So, either additive to postpone the wear that will come or get valve seat inserts. Benefit is you can do a cylinder head refresh at same time... maybe even do some other upgrades

Mike Ward

I'd suggest you had some other defect with those heads. Lead was commonly but mistakenly said to 'lubricate' the valves which is incorrect. There was no change in GM valves or valve guides when the modified heads were introduced in 1971. Only the valve seats were induction hardened.

There's plenty of examples around of pre-71 Corvette heads around that have been operated on unleaded fuel for decades without issue.

There's also lots of examples of heads being scrapped during modifications for hardened seats when the shop accidentally cuts into the cooling passage.

Basicman

Finally a subject I know something about. I worked in the auto industry back in the 70's when unleaded fuel just hit the market. We ran a series of tests using leaded and unleaded fuel. These tests were conducted all over the country to get a variety of conditions. Arizona was the most severe. I will be brief. No, you do not need hardened valve seats. We tested engines that had never seen leaded fuel and only on severe conditions like heavy loads and trailer tow did we see any valve "sinking." If the car got any leaded fuel including the factory fill that included lead at the time, (7 gallons) the amount of valve Sinking was significantly reduced to the point it was negligible. Even if no more leaded fuel was added. In other words, a little TEL goes a long ways. The most severe valve sinking was on dynamometer and if you have ever observed an engine on a dynamometer, you know your Corvette will never see that amount of abuse. That being said, I am in the process of rebuilding my factory sealed 65 327/350 and I am going to treat the heads to new valves only if needed and I will not add hardened seats and will not even grind the seats if they are in good shape. Nothing like factory sealed engines that have not exhibited any issues for 50 years.