Fuel Finder

Race Fuel 101: Lead and Leaded Racing Fuels

It’s been almost 40 years since lead was phased out of pump fuels. Today, there are an increasing number of racers who never bought a drop of leaded gasoline for the family sedan back in the day. Understandably, we get a fair amount of questions about lead and why it’s used in some racing fuels.

Lead is an element (symbol Pb) and has a number of industrial uses. For racing fuels, lead is not used by itself… it is actually added in the form of Tetraethyl Lead (also known as TEL). TEL is a liquid mixture which makes it more easily stored and injected.

Lead is used in racing fuels because it is a very effective octane booster. As a matter of fact, leaded fuels are often credited for allowing higher compression, higher efficiency engines in World War II era aircraft. Increased power made some WWII airplanes like the P-51 Mustang legendary performers!

Just a little bit of lead in gasoline can raise octane up to 20 octane numbers. A great example of this can be seen by comparing Sunoco MO2X Unleaded to the leaded version – Sunoco MO2X. Both fuels have exactly the same composition; the only difference is one has lead and one doesn’t. MO2X Unleaded has a 97 octane rating while the leaded version achieves a 112 octane rating. Though one is 15 octane numbers higher than the other, both share the same fuel combustion properties. Both fuels are oxygenated, both provide great throttle response, and racers have the choice of running an unleaded fuel if 97 octane is sufficient.

Another advantage: lead does not have any significant effect on overall combustion properties. This allows us to specify certain hydrocarbons in a blend to achieve desired fuel properties, then add varying amounts of lead to target a an octane level. This is why the myth about high octane fuels burning slower is exactly that – a myth.

We also get questions about lead being used to keep old engines running longer. We do not add lead specifically to promote valvetrain life in older engines, but indeed that is a benefit, especially for vintage racers. Many older engines were built without hardened valve seats because lead in fuels helped extend the useful life of exhaust valve seats. If you own a mid-‘70s or older race car that still uses the stock cylinder heads, consult with your engine builder about leaded fuels.

Leaded fuels should not be used where oxygen sensors and/or catalytic converters are used. While it is rare to see a race car equipped with a catalytic converter, the use of oxygen sensors on race engines is becoming more common. Fortunately, we offer high octane unleaded fuels to satisfy most of these race cars.

We still hear from a few racers who use oxygen sensors with leaded race fuels in their race cars. The useful life of an oxygen sensor used with a leaded fuel is hard to predict, but one thing is certain: it will eventually fail. Some oxygen sensors can last a whole race season when used with a leaded race fuel, while others may only last one race. The useful life depends heavily on the application. Many racers running oxygen sensors and leaded fuels are able to use the oxygen sensor just for tuning purposes, then once tuning is done they’ll pull the sensor out and plug the sensor mounting bung. This is probably the best way to utilize an oxygen sensor where a leaded race fuel is required, and it ensures a much longer useable life for the sensor.

That’s the short version of why lead is used in some racing fuels. If you have any additional questions, don’t hesitate to call the Sunoco Race Fuels Team at 800 Race Gas (800-722-3427) or send us a message from our Contact page.