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Re: What gas do pre-1974 LEADED gas cars run? [Re: wowthisexists] #5362936 02/29/20 12:36 AM
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wowthisexists Offline OP
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So, leaded cars can use unleaded?
Then what was the point of the lead if it's not even needed ?

Re: What gas do pre-1974 LEADED gas cars run? [Re: sloinker] #5362954 02/29/20 01:19 AM
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CR94 Offline
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Originally Posted by sloinker
... Valve recession is real for earlier engined vehicles ...
Yes, especially if the engine is operated above 3000 RPM, according to a study published in the SAE magazine a few years back.


2011 Toyota Prius now at 110K
1981 Mazda GLC (323) retired at 606K
1972 Subaru DL retired at 190K
1954 Chevrolet retired at 121K
Re: What gas do pre-1974 LEADED gas cars run? [Re: wowthisexists] #5362993 02/29/20 05:05 AM
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TriMoto Offline
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I seen a video from Chrysler dated 1973 saying to use lead substitute every 4th tank of gas. I've used MMO every other tank in my 66 Dodge Polara 383 for the past 2 years so far with no issues. The commercial lead subs are a joke/scam to me. I bought a case of Gunk lead substitute and it is repackaged kerosene at a crazy price. MMO, trans fluid, kerosene, 2-cycle oil will do the job IMO.

Re: What gas do pre-1974 LEADED gas cars run? [Re: wowthisexists] #5363025 02/29/20 06:31 AM
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kschachn Offline
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Originally Posted by wowthisexists
Can't get leaded gas no more
so what do LEADED cars use for gas?

So what vehicle do you have exactly and what is the year it was built?


1994 BMW 530i, 252K
1996 Honda Accord, 288K
1999 Toyota Sienna, 434K
2000 Toyota ECHO, 284K
Re: What gas do pre-1974 LEADED gas cars run? [Re: wowthisexists] #5363085 02/29/20 08:33 AM
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Cujet Offline
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It's OK to mix 100LL Avgas with non ethanol gasoline. The blend's octane may actually be higher than the ratio's would indicate, due to the "lead response rating" of the non ethanol gasoline. A 50/50 blend more than matches the octane of yesterday's 100 octane fuels (which were really 95 octane when rated (R/M) /2 )

The very high octane ratings of the 1960's were "Research" octane numbers. Today's fuels (in the USA) are (R/M) /2 rated. Not really comparable.


People who count on their fingers should maintain a discreet silence.
Re: What gas do pre-1974 LEADED gas cars run? [Re: wowthisexists] #5363344 02/29/20 12:51 PM
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y_p_w Offline
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Originally Posted by wowthisexists
So, leaded cars can use unleaded?
Then what was the point of the lead if it's not even needed ?

I guess the issue with many of these engines was that lead helped to lubricate and cushion certain parts by forming a protective layer. It was just something that engine makers took advantage of. However, the primary reason for lead was that a small amount was a highly effective octane rating booster. If the parts weren't designed around this, they would still work fine with unleaded with an adequate octane rating.

Re: What gas do pre-1974 LEADED gas cars run? [Re: wowthisexists] #5363355 02/29/20 01:05 PM
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Both of mine have hardened valve seats. The MG got them a few years ago, while the Marina got them back in the 80s.

The MG is at 9.5:1, and runs top tier 93 along with the timing advanced a bit over standard(I could run it on 89, but don't like how much I have to retard the timing, and the accompany low RPM power loss). The Marina is still at its emission-strangled 8.0:1, and gets whatever cheap 87 I want to put in it.

From about 72 onward, the British "A" and "B" series engines had induction hardened valve seats from the factory(series 18V on the 1800cc B engine). This, along with some other smog accoutrements and the associated temperatures, tends to cause cracking from the exhaust seats. If one is caught before it cracks, or at least cracks badly, usually it can last more or less forever if its fitted with a proper hardened steel insert seat.

I would not be averse to the occasional use of 100LL if I were running something without hardened seats.


2010 Lincoln MKZ-Mobil 1 5W-30
1970 MG MGB Roadster-Valvoline VR-1 20W-50
1974 Austin Marina GT VR-1 20W-50
Re: What gas do pre-1974 LEADED gas cars run? [Re: wowthisexists] #5367372 03/04/20 05:41 PM
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DGXR Offline
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There are many lead substitute products available, pick a reputable name brand and dose your fuel as directed. You may need to use a higher octane level, but maybe not. I understand some of the old school gasolines back in the day had lead to increase the octane/anti-knock index. Experiment a bit and use whatever works.


1995 Corvette coupe LT1 6-speed
2006 Tacoma 2.7 Base SR5 AC
1999 Yamaha YZ400FL
2003 Honda XR400R
Re: What gas do pre-1974 LEADED gas cars run? [Re: wowthisexists] #5375034 03/12/20 10:15 PM
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wings&wheels Offline
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Must've missed this thread....

If you do use a lead substitute, get one that's been proven to work. One of the British historical vehicle groups did extensive testing on lead replacement additives and only recommended a few. Sadly, not many were available here, but Redline is and was one of the recommended additives. That is all I use, plus the very occasional shot of 100LL if I have one of the oldies with me as I preflight.

Google lead substitute test and you should be able to find the British study.


'05 Lotus Elise S/C
'85 Land Rover 90 diesel
'74 Triumph TR6
'74 BMW 2002
'72 Land Rover Series III 88"
'99 Porsche 996 (Wife's)
'01 Porsche Boxster S (mostly Wife's...)
Piper Pa28-236


Re: What gas do pre-1974 LEADED gas cars run? [Re: wowthisexists] #5375038 03/12/20 10:21 PM
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wings&wheels Offline
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Found it, and way back when I asked Redliane as was told that their lead substitute here is the same as in the UK:

"Accept These Substitutes
The following additives have been tested as being effective against valve seat recession, and are approved for use by the Federation of British Historic Vehicle Clubs.

Delta Oil

Red Line Lead Substitute Employing sodium to deliver the goods, Red Line Lead Substitute is said to clean intake systems, carburettors and injectors in addition to preventing valve seat recession. It was developed in the U.S.A. Delta Oil Ltd., Unit F1, Market Overton Industrial Estate, Market Overton, Rutland, LE15 7PP. Tel. 01572 768311.Website: http://www.redlineoil.co.uk"


'05 Lotus Elise S/C
'85 Land Rover 90 diesel
'74 Triumph TR6
'74 BMW 2002
'72 Land Rover Series III 88"
'99 Porsche 996 (Wife's)
'01 Porsche Boxster S (mostly Wife's...)
Piper Pa28-236


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