Tech Corner

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!

Specific Gravity

Definition:  specific gravity (noun) - the ratio of the density of any substance to the density of some other substance taken as standard, water being the standard for liquids and solids, and hydrogen or air being the standard for gases.

For fuels, specific gravity can be determined by dividing the density of the fuel (in units of pounds per gallon) by the density of water (8.325 pounds per gallon).  Let’s look at one example.

We get a lot of questions about fuel metering changes required for oxygenated fuels... and that is a good thing, because racers should be asking those questions.

Luckily, the answer is not necessarily complicated.

Let’s look at Sunoco EXO2 for instance.  It’s a good fuel to use as an example because it contains 10% (by weight) oxygen.  Without proper fuel enrichment, you won’t find the power you’re hoping for, and in fact the engine may not even run well.

Alcohols like methyl alcohol (methanol) and ethyl alcohol (ethanol) are often used in race fuels.  Sometimes they are a small part of the fuel and sometimes they are a primary component of the fuel.  Methanol is commonly used “straight” – that’s why it’s called racing alcohol by many.  Ethanol can also be used straight, and some racers do, but it’s more common to hear about E85, a blend of about 85% ethanol.

Much has been said about the octane rating of alcohols.  However, technically speaking, the octane ratings of alcohols can not be measured.

All octane test engines, as defined in the octane rating procedures set forth by the American Society for Testing and Materials (ASTM), are carbureted.  Air/fuel ratio adjustments on octane engine carburetors are limited and can not accommodate the extremely different air/fuel ratio requirements of pure alcohols.