Fun With Hypermiling - Part 3

Part 1 - Introduction - "What is Hypermiling?"
Part 2 - Test Hypotheses
Part 2 - Fun with air filters

In Part 2, you learned about what I'm hoping to conclude from these tests, as well as the test subject itself - our trusty 1994 Toyota Corolla.

The car typically got an average of 34 mpg with my 33.5-mile one-way daily commute consisting of about 17 miles of hilly back roads and 16 miles of stop-and-go traffic. My typical driving style could be described as "average".

The first thing I tried was improving the airflow to the engine intake. By allowing more airflow, I hoped to reduce the airflow restrictions, making it easier for the engine to suck in air (imagine trying to breathe through a coffee stirrer versus a normal straw). My hypothesis was that this would create less work for the engine, thus making it more efficient.

The downside was that with increased airflow is more oxygen. When the engine's sensors detected more oxygen, there's a possibily that the computer will add more fuel to compensate. With this car being an OBD-1 car, there was no way to read the sensors accurately, but eventual mileage would indicate the increased use of fuel.

The stock airbox consisted of a tube that ran from the front of the engine bay to a large, empty box that held the air filter. The engine pulled air from the tube, into the box, through the filter, through the airflow meter (built into the top of the box), and down another duct to the engine intake, and into the cylinders.

I removed the tube and lower portion of the box. Then, I secured the air filter to the airflow meter, which still forced all intake air through the filter.

Much to my surprise, this modification netted about 1 mpg for an average of just over 34mpg.

While this doesn't generate specific numbers on fuel use, there is the possibility that the car realized more airflow than what that 1mpg increase showed, but may have been adding more fuel to compensate for the extra oxygen.

Whatever the situation, the car consistently saw that extra 1mpg with this intake modification. The cost was free and, given the average fuel consumption rate of me and the car, would have saved about 572 miles of fuel per year, which equates to 16.8 gallons. At $3.44 per gallon of 87 octane, that's a savings of $57.79 per year.

It should also be noted that the filter was an OEM-style paper filter, so additional mileage may be able to be obtained with a higher-flowing cotton filter.

In the next installment, we talk tires.


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