Any classic car owner wonders if they ought to apply a lead additive to their fuel and what is the best lead substitute for classic cars. Tetraethyllead was applied to gasoline for decades to minimize engine knock and help avoid valve-seat recession.
When the dangers of lead became apparent, authorities started phasing it out in the 1970s. But what about old car motors from the 1950s and 1960s that were designed to run on leaded gas? Is a lead replacement required?
Why was lead applied to gasoline in the past?
Let’s start with the primary reasons why lead was applied to gasoline in the first place.
- Increase the octane level to further mitigate engine knock
- Prevent the recession of valve seats
What exactly is “engine knock,” and why is it important?
The term “knock” refers to the unregulated and explosive burning of a hydrocarbon fuel, such as gasoline, in the combustion chamber. It makes a banging or pinging sound, drains the motor’s power, and can cause significant motor damage if left unaddressed.
The octane level of fuel determines its propensity to knock. Lower numbers indicate greater knock proclivity, whereas higher numbers indicate greater knock tendency. Knock can be removed by using the proper octane number.
Lead is impervious to pre-ignition
The octane score of gasoline shows its ability to survive compression prior to igniting. The piston moves up the cylinder during operation, compressing the air/fuel combination in anticipation of ignition.
Compression heats the air/fuel combination, allowing it to combust more quickly and fully. Compressing the air/fuel mixture also increases the volume loaded into the cylinder, increasing strength and performance.
Where all other considerations are equivalent, motors with higher compression ratios normally generate more energy.
However, if the compressed, hot fuel approaches its ignition point too quickly, it will self-ignite before the spark plug fires. This throws off motor timing, decreases power, and can cause motor damage.
To stop pre-ignition, use fuel with the right octane level for your engine. Higher-octane gas is needed for engines that use higher compression.
In the 1920s, chemists learned that Tetraethyllead applied to gasoline was a cost-effective alternative to pre-ignition and improved engine efficiency.
Lead also provided protection against the recession of valves
Lead had also evolved as an attractive method of preventing valve-seat recession, which tends to occur under high-load, high-heat, and high-rpm conditions.
As the heated exhaust valve pounds against the seat of the valve thousands of times a minute, the two components will briefly fuse together in a process known as “micro welding.”
When the valve is opened, the micro weld rips apart. As this happens thousands of times, the seat of the valve degrades to the point that the valve no longer sits properly. This results in power and compression reduction, as well as a structural failure if the valve snaps off.
The advent of hardened valve seats
We became aware of lead’s harmful impact on the environment, human health, and automobile catalytic converters by the middle of the 1970s. Engineers started developing engines with unleaded gas in mind while authorities worked to remove lead from fuel (and other products.) They utilized hardened valve seats, which are more resistant to valve recession, to prevent micro welding.
That’s fine for engines from that period and modern engines, but what about your vintage car engine, which was made before hardened valve seats were widely used?
Lead replacements offer a solution
To address the problem, many car enthusiasts mix a lead replacement into their fuel. Lead replacements contain chemicals that form a sacrificial coating to prevent micro welds and cover valve seats; they can be purchased at any auto parts store or online.
Do I require a lead replacement?
This is a garage controversy that never appears to be resolved, just like the controversy over the right motor oil brand or whether or not to flush a high-mileage car engine.
To begin, if you’ve reconstructed the engine or worked on the cylinder heads, it’s probable that hardened valve seats were used, which means a lead replacement isn’t needed.
If the motor is original and has stock valve seats (i.e. not hardened,) we advise using a lead replacement for additional safety.
This is particularly valid if the operational conditions are borderline “severe.” It doesn’t take long for a high-compression-ratio, cast-iron engine of that age to crank up the heat, crank up the rpm, and run in conditions that support valve-seat recession. Using a lead replacement gives an assurance that your classic is secure.
So, which lead replacement will you use?
DOMINATOR® Octane Boost by AMSOIL: The Best Lead Substitute for Classic Cars
It includes a good dose of MMT (Methylcyclopentadienyl manganese tricarbonyl,) a metallic additive that forms a sacrificial layer on valve seats to help avoid recession and keep the engine running solid. It works fantastically as a lead replacement.
Key Benefits of AMSOIL DOMINATOR® Octane Boost
AMSOIL DOMINATOR® Octane Boost (AOB) enhances engine power and responsiveness in both four- and two-stroke gasoline-powered engines by boosting octane by up to four numbers.
Just a single application of this lead substitute additive significantly lowers engine knock, increases ignition, and assists in cleaner fuel combustion. DOMINATOR® Octane Boost is the octane boost that is suggested for both high-performance racing and off-road purposes.
Most consumers find that one 12-ounce bottle of DOMINATOR® Octane Boost for every 15 gallons of fuel offers the best performance improvement. DOMINATOR® Octane Boost is also an outstanding lead replacement at the same treat rates in older off-road motors, collector cars, and leisure vehicles.
- Enhances performance
- Effective at removing carbon deposits
- Increases power
- Decreases engine knock
- Enhances ignition
- Enhances ignition
- Assists in the clean-burning of gasoline
- Inhibits corrosion