Leaded gasoline

[Michael G.]

I just read an article were the N.C.O.A has the corvette usung leaded gasoline up to 1974. Is it to be understood that all up to 1974 should have lead added to the gasoline unless altered to accept unleaded? Thanks, Mike

[Donald T.]

Re: Leaded gasoline

Michael,

You might want to check the archives as there is a treasure trove of information on octane and leaded gas. Bottom line is that it should not be necessary. TEL (lead) was used as an octane booster. As long as your car is not knocking or pinging on premium pump gas, then it does not require more octane. Others more knowlegable than I have stated that the valve seat protection offered by TEL is highly over rated.

[Bill C.]

Re: Leaded gasoline

I think that GM was already altering valve seats etc.. to run LL or no-lead as early as 1971.

If your car is pre 1971, then you will need to retrofit parts to work with unleaded fuels. I would include carburators and rubber parts in this list, specially since ethanol is now blended in gas. It does bad things to old rubber parts, and floats in carbs.

Some will say that you do not need to worry about valve seat issues, particularly if you don't drive the car hard and it is not a daily driver etc.

I personally blend TEL in my fuel - it keeps my engine running cooler and it idles much better. It blends lead at levels lower than 100LL contain.
-- just a personal preference here.

Hope I did not make it more confusing for you ---

[Kenneth B.]

Re: Leaded gasoline

I just read an article were the N.C.O.A has the corvette usung leaded gasoline up to 1974. Is it to be understood that all up to 1974 should have lead added to the gasoline unless altered to accept unleaded? Thanks, Mike

I have been using unleaded gas in all my pre 74 Corvettes with no problem. As long you don't beat on the car & keep the RPM'S reasonal I don't think it's a problem. I don't put a lot of miles on my cars thought.
KEN

[Michael W.]

Re: Leaded gasoline

You might be looking at the statement the wrong way around- unleaded gas was not universally available in 1974 so all cars had to be able to run on regular leaded.

This does not mean that the vehicle must run on leaded or that it would run better or longer.

In any case, I've never heard or seen a bonafide case of a Corvette suffering due to lack of lead. Octane level is a different story.

[Fred Y.]

Re: Leaded gasoline

Interesting Ken,My 67 400 air coupe runs BAD and has a very poor undependable idle when I use anything other than a 50/50 110 leaded/93 unleaded blend.Not to mention the exhaust smells great too!!

[Larry M.]

Re: Leaded gasoline

Fred:

If your car requires the fuel mix you describe, then it is either not stock or something is wrong with the carb, distributor, or initial spark advance.

I agree that the leaded racing fuel has a unique (nice) smell, but you shouldn't need it unless the engine has been modified.

Larry

[Kenneth B.]

Re: Leaded gasoline

Interesting Ken,My 67 400 air coupe runs BAD and has a very poor undependable idle when I use anything other than a 50/50 110 leaded/93 unleaded blend.Not to mention the exhaust smells great too!!

May be the carb needs adjusted , check timing & quit smelling the exhaust you could go blind.
KEN

[Michael G.]

Re: Leaded gasoline

Thanks to you all. My 71 has been running fine on premium unleaded for the 14 months I have owned it and I just needed to know that I can continue without doing harm. You guys are the best!! Mike

[Fred Y.]

Re: Leaded gasoline

Larry,I have the original carbs on my car (rebuilt),the Distributor was rebuilt last Spring,& when the L/L electronic ignition failed last Summer I went back to good OL points.And she's never run better----As long as I mix the gas!!----As far as engine mod's-??None that I know about,she's stock.But sometimes I really think I shoud have the carbs looked at again or just put them in a box & go with a set of brand new Holley replacements.

[Paul H.]

Re: Leaded gasoline

The engine in my 65 (L79) was last rebuilt in 1987 and runs fine on 93 pump gas with no lead additives. No hardened valve seats. I run it an average of 3,000 miles per year. No problems. Engine runs as good as it did when it was rebuilt 22 years ago. None of my older Corvettes have had any problems with pump gas. I think the need for lead is mythical.

[Grant M.]

Re: Leaded gasoline

This issue has been dealt with repetitively over the years and a search in the archives will disclose plenty of opinion/fact/information. From my own experience/information garnered from various sources, an older Corvette (less the highest output engines such as an L-88 etc) will run acceptably on modern unleaded fuels, provided the octane level is adequate and, more importantly, provided the load on the engine is not maximized (ie: hard acceleration/trailer towing. etc). A colleague asked the "lead versus unleaded" question of Shell Oil Technical staff some years ago and received that advice in return. As to valve seat recession, it was noted in the reply that without hardened valve seats there would be recession over time, but given the relatively limited mileage accumulated on the older Corvettes, this shouldn't be a major concern.

I have a '65 L-75 that was rebuilt in 1987 (without hardened seats--my oversight, but retaining its 10.5:1 stock CR and camshaft) and it runs fine on Sunoco 94 Octane unleaded available at stations here in Ontario. I have on occasion added TEL via 104 Octane "Real Lead", and some of Jack Podell's "Lead Supreme 130" and sometimes I've mixed in some (supposed) 110 Octane "Racing Fuel" available in the summer here in Ottawa. I can't say I've seen a whole lot of difference, although that's a subjective judgement on my part and I haven't measured operating temperature (accurately), quarter-mile/0-60 times etc to assess the effects.

As I recall, GM vehicles from 1971 on were noted as being able to run on the new "low-lead" fuels and then from 1975, with introduction of catalytic converters, on unleaded fuel.

grant

[Stuart F.]

Re: Leaded gasoline

I have a 63 L-76 340 hp and have used an additive ever since I heard/perceived my first knocking many years ago. I believe mine to be a single gasket actual 11.25 to 1 CR as it passes the feeler gauge check for head gasket thickness (.015"). I had backed off my timing back in the 70's, but since using TEL, I can now run an enhanced mechanical advance curve with full initial timing. It allows the engine to run cooler and idle smoother, and I admit I like to take it out on country roads and flog it. It readily goes from "stop-and-go" traffic driving to the red line on a highway on ramp. It runs the cost up a little and takes more time to fuel up, but I don't mind as it has become a ritual - something like what we used to do in the pits (blend fuel).

Stu Fox

[Michael W.]

Re: Leaded gasoline

I can't say I've seen a whole lot of difference, although that's a subjective judgement on my part and I haven't measured operating temperature (accurately), quarter-mile/0-60 times etc to assess the effects.

As I recall, GM vehicles from 1971 on were noted as being able to run on the new "low-lead" fuels and then from 1975, with introduction of catalytic converters, on unleaded fuel.

grant

Hi Grant,

Long time no speak. Glad to see that you're just down the road from us in the nation's capital. Please tell Harper to smarten up next time you see him.

There's a lot of myths and misunderstandings surrounding the need and/or benefits of leaded gas, one of which is the engine temp/idle quality issue. These issues are more to do with fuel percolation (vapour pressure) and not whether the fuel has lead or not.

You were fortunate in NOT having your valve seats replaced as this is completely redundant on a Corvette.

[Duke W.]

Re: Leaded gasoline

major concern.


As I recall, GM vehicles from 1971 on were noted as being able to run on the new "low-lead" fuels and then from 1975, with introduction of catalytic converters, on unleaded fuel.

grant

Close. By 1970 GM realized that catalysts would be required to meet 1975 emission standards. So in order to promote the production of unleaded fuel (and the technology of the time allowed for 91 RON unleaded fuel, which is equivalent to today's 87 PON) GM management decreed that ALL 1971 engines would be tuned to operate on 91 RON unleaded fuel. This required all high compression premium fuel engines to have their compression ratios dropped about two points and some slight spark advance map retuning of regular fuel engines.

At the time leaded regulars were in the range of 93-94 RON. Unleaded fuel was phased in to all markets over the next four years, and since unleaded 91 RON was usually more expensive that leaded regular, most people used leaded regular in these pre-catalyst engines.

In 1975 unleaded fuel became mandatory with catalysts, and a restrictor was added to fuel filler necks, which prevented the larger nozzle of unleaded fuel pumps to be inserted into the filler. (Then as now the unleaded fuel nozzle was smaller than the traditional fuel nozzles used for leaded fuels.)

In this era GM found increased valve seat recession with unleaded fuel on some engines run at high speed and load for extended periodes, and as a result they added exhaust valve rotators and induction hardened exhaust valve seats on some engines including some Corvette engines in the seventies.

But most owners with pre-seventies engines have not experienced valve seat recession in the low mileage, low average load service that most vintage Corvettes see.

As leaded premiums were phased out in the eighties, higher octane unleaded fuels became available, so there was never a time when you could not buy sufficient octane for a vintage high compression engine, although big blocks typically have a higher "octane appetite" than small blocks, but most detonation problems could be solved with a few degrees reduction of initial timing.

The effects of lead are long lasting, so mixing in some leaded race gas or 100LL avgas every few thousand miles will maintain a thin lead oxide film on the valve seats if this issue causes you to loose sleep.

"Octane additives" are a waste of money.

Duke