I have an old '73 240-Z that I am fixing up in class. Once I get it running, will I need to add something to the gas? I know that old cars ran on leaded fuel, the lead lubricating the parts as it ran. But leaded fuel is no longer available, as it was an environmental disaster. Is there a way of running it on un-leaded gas?

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    By 1973 U.S. bound vehicles came from the factory with valve seats designed to run on very low lead fuel.The levels of lead started to drop in 1971.
    – mikes
    Commented Apr 10, 2012 at 23:41

4 Answers 4


Yes, you can buy additives that can be mixed with unleaded fuel. I found a list suitable products on the AA website:

Suitable additives

There are several proprietary lead-replacement additives available for 'DIY' dosing of unleaded petrol – these will increasingly be found in accessory shops and filling stations.

Additives have been in use in Germany, Austria, Switzerland and New Zealand for some years with no reports of problems, though there are reservations about the effect of a sodium based product on turbo-charger blades.

Additives may be phosphorus, sodium, potassium or manganese based – and are quite satisfactory used at the correct dosing rates in appropriate vehicles.

The following fuel additives were found satisfactory in engine durability tests set up by the British Historic Vehicle Clubs:

* Millers VSP Plus, (manganese)
  Millers Oils Ltd. Freephone 0800 281 053
* Red Line Lead Substitute, (sodium)
  Delta Oil Ltd. 01476 861 195
* Superblend Zero Lead, (potassium)
  Superblend Lubricants Ltd. 0116 291 1700
* Castrol Valvemaster & Valvemaster Plus (phosphorus)
  Castrol Ltd. 01793 452 222
* Carplan Nitrox 4-Star (potassium) & 4-Lead (manganese)
  Carplan Ltd. 0161 764 5981

In general, it's best to choose one product and stay with it, though some inter-mixing will be inevitable at times.

Where the vehicle manufacturer originally recommended the use of, for instance, one tank of leaded petrol to four tankfulls of unleaded, if you are using an additised fuel the additive should be used in every fill.


Have you looked at Gunk or other similar products?

Autobarn lead substitute


It should run on today's pump gas, though you'll probably find it runs better on plus or premium. Tetraethyl lead prevents valve wear and serves as an anti-knock agent. Installing hardened valves and valve seats in the engine takes care of the first, while high octane gas will take care of the second. You could reduce the engine compression to run it on regular pump gas. An additive (lead or alternative) as BG100 is suggesting works, too.

Muscle cars didn't suddenly stop running when leaded gas was phased out. They just didn't run as well and maybe ended up needing a rebuild sooner than they would have otherwise.


I believe there is no way to run a vehicle designed for leaded gas to run on unaltered unleaded gas.

Most auto parts stores sell lead additive to be used in unleaded gas for older cars that require leaded gas.


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