The gasoline you use to power your Corvette down the road is blended with several different goals in mind. The blend of gasoline is changed for the seasonal weather changes, plus the federal, state, and local environmental regulations that may mandate the use of reformulated gasoline. There is also a push to increase the use of ethanol or alcohol-based additives to both reduce fuel-related emissions and lessen our dependence on foreign oil. This means the blend of gasoline you use will not only vary from brand to brand, but also will change by the season and the part of the country you buy your gas in. As the level of ethanol or other alcohols is increased, the fuel efficiency of the engine will decrease. The fuel efficiency will decrease because gasoline has more energy per gallon than ethanol or alcohol-based fuels. An engine running on alcohol-based fuel runs at a richer air/fuel ratio than an engine running on gasoline. The stoichiometric or chemically ideal air/fuel mixture for an engine running on gasoline is 14.7/1, for an engine running on E-85 (85-percent ethanol and 15-percent gasoline), it is an air/fuel mixture of 10/1; an engine running on ethanol is an air/fuel mixture of 9/1.
A modern fuel-injected engine computer will make the air/fuel mixture adjustments needed so the engine will run its best with the blend of gasoline you are using. The ethanol and other alcohol-based additives that are blended into today's gasoline will cause a noncomputer-controlled carbureted engine's air/fuel mixture to go leaner as the percentage of alcohol-based additives is increased. The reformulated gasoline of today burns at a different rate than the leaded gasoline of days past and will cause the air/fuel mixture to be at least 3- to 5-percent leaner than it was with leaded gasoline. (Please see the tech articles in our June and July '06 issues on tuning a noncomputer-controlled carbureted engine to run on reformulated gasoline if you want more information on this subject.)
Power-Robbing, Fuel-Related Deposits
As your engine consumes the fuel it uses to make the power that moves your Corvette down the highway, deposits are building up in the combustion chamber and on the engines valves that will reduce the engine's power. Most of the gasoline that you buy at your local gas station has additives that are designed to reduce the formation of these power-robbing, fuel-related deposits. However, it may not be of high enough concentration to prevent or remove any existing deposits. The use of a fuel-system cleaner, such as Techron Concentrate Plus from Chevron, on the same schedule that you change your engine's oil should be part of normal vehicle maintenance on both fuel-injected and carburetor-equipped engines. A high-quality fuel-system cleaner will help clean and prevent the carbon deposits that form in the combustion chamber and on the intake valve as the engine burns the gasoline it uses to make power.
The fuel-related carbon deposits that form in the combustion chamber and on the intake valve can create a wide variety of engine-performance problems. The engine will produce less power as the deposits on the intake valves and intake ports restrict the airflow into the cylinder. These carbon deposits can also absorb gasoline like a sponge when you are starting a cold engine, and thus cause the engine to have extended crank times before it finally starts. The carbon deposits that build up on the piston and in the combustion chamber can cause the engine to have detonation or pinging problems. This will cause the knock-sensor system on a computer-controlled, fuel-injected engine to retard the timing.
How Long Will Fuel Live In Your Tank?
The gasoline sold at your local gas station will begin to degrade in a time frame of one to six months after it is blended at the refinery. The factors that help determine how quickly the gasoline degrades are the quality of the gas and the additive package that is blended into the gasoline. The temperature and humidity that the gasoline is exposed to while it is in the gas tank will also cause the gasoline to degrade. As the gasoline begins to degrade, some of the lighter elements that are in the gasoline, such as butane, will evaporate with time, and the fuel will begin to turn into a sticky/gummy/varnish-like substance. Most of the gasoline that you buy at your local gas station contains a component known as olefins, as this gasoline ages or when it is exposed to the heat of an engine compartment it will begin to form sticky gum-like deposits. The deposits left behind as the fuel ages or boils will cause problems with every part of a carbureted or fuel-injected engine's fuel system.
An unleaded race fuel, such as Rockett Brand 100 octane, is designed to have a shelf life of up to two years; part of this longer life is because it contains less than 0.5-percent olefins. Depending on the local and state environmental regulations you have in your part of the country, the gasoline you buy at your corner gas station may have up to 20-percent olefins in it. A gasoline storage stabilizer, such as STA-BIL from Gold Eagle, can also be used to help slow the gasoline's ageing process, but you are ahead of the game if you start with a low-olefin gasoline, such as Rockett Brand 100 unleaded racing fuel.
Adding Performance To Gasoline
There are a lot of additives on the market that claim to add performance to gasoline, but few live up to the claims they advertise. We have recently been working with a new fuel catalyst from Chevron called PurEscape, and it actually did increase the power and drivability in each car we tried it in. The active ingredient in PurEscape is from a family of chemicals known as fatty acid polyols; the exact formula is patented and a trade secret. When the PurEscape is added to the reformulated gasoline of today, both the engine performance and drivability we experienced showed us noticeable improvements. It is normal for a spark-ignited engine to have a certain amount of variance in combustion efficiency from cycle to cycle. The PurEscape improves the gasoline's combustion properties and makes it easier for the spark plug to ignite the fuel in the combustion chamber, and thus allow the combustion process to become more consistent. When the PurEscape is added to the gasoline it will help release the gasoline's energy faster during the combustion process, resulting in higher average cylinder combustion peak pressures.
Performance Improvement Tests
The test vehicle we will reference here is a '97 Corvette LS-1 engine with an automatic transmission, but the results have been as good on everything from a four-cylinder, imported, economy car; a carbureted Corvette; and even a street rod with a carbureted ZZ-4 engine. The performance improvements were the most noticeable during our tests on the four-cylinder, imported, economy car. The driver of the imported, economy car said the PurEscape made her car feel like it was on steroids and also got more miles to the gallon of gasoline each time she used PurEscape in a tank full of gasoline.
We used an accelerometer to measure the g-force that was created as we accelerated from a dead stop to 60 mph so we could compare the gains we experienced as we tried the four different fuel blends. We started with a major brand of premium-unleaded gasoline in the gas tank, and then we added the PurEscape to the premium-unleaded fuel. We next removed the premium gasoline from the gas tank and replaced it with Rockett Brand (formally Union Oil Racing Gasoline) 100-octane, racing, unleaded gasoline, as a final test we added the PurEscape to the 100-octane gasoline.
The first acceleration tests were used to establish a performance baseline with the premium-unleaded gasoline in the Corvette's gas tank. We performed three wide-open throttle acceleration runs on a level road from zero to 60 mph with the traction-control system engaged. The readings from the accelerometer showed we had peak g-force readings of 0.62g, 0.60g, and 0.63g during the three acceleration test runs.
The same acceleration tests on the same day and location with the premium-unleaded gasoline and PurEscape mixed in gave us peak g-force readings of 0.69g, 0.70g, and 0.69g. There was also a noticeable gain in drivability, and the seat-of-the-pants power gain was noticeable to both the driver and the passenger.
A repeat of the same acceleration tests again on the same day and same location with the 100-octane Rockett brand race fuel gave us 0.72g, 0.73g, and 0.73g. There again was a noticeable gain in drivability, and the seat-of-the-pants power was noticeable to both the driver and passenger with the 100-octane fuel over both the pump gas and the pump gas with PurEscape.
As a final test, we added the PurEscape to the 100-octane race fuel and repeated the acceleration tests, this time we were not sure if we gained any power, and the g-meter recorded runs of 0.73g, 0.74g, and 0.72g. We think there may be some minor improvements when the PurEscape was added to the 100-octane fuel, but we are not sure. Our tests also pointed out that both the premium unleaded gasoline with PurEscape and the Rockett Brand 100-octane race fuel had more consistent acceleration results, better drivability, better throttle response, and more engine power than we had with the untreated premium gasoline we were using when we started the performance tests. We have found that in every car we have tried the PurEscape in there has been an increase in gas mileage, which was a very nice side benefit in these days when gasoline is in the $3-a-gallon range.
The gasoline you use and the additives you put into the gasoline can add performance to your Corvette, and in some cases will even allow it to perform better than when it came off the showroom floor. A clean fuel system with the correct blend of gasoline and additives will give you the best performance from your Corvette.