I don't want to sound like the fine print here, but it depends on the test. Simply driving a car without scientific equipment exposes it to too many variables.
All of the fuel economy tests Enerpulse reports are performed on an eddy current dynamometer using the EPA US06 driving cycle. We condition the car (tire pressure, fuel, new plugs) and tap into the fuel line with a digital flow meter linked to a computer to measure real time fuel flow. We then run the spark plug followed by the pulse plug and measure the difference in fuel consumption. The test driver has to follow the driving cycle on the computer screen and match it precisely. The test lasts 596 seconds at an average speed of 48 mph and includes acceleration ramps up to 80 mph. We test practically every day and have seen some gain in every vehicle we test. On average we get 6% improvement across all vehicles. For full test details see
http://www.pulstarplug.com/pdf/epep.pdf.
I know that people who buy our product might feel good about our scientific tests, but they really only care about saving money. Most of them do. But, we concede not everyone will ultimately feel it in their wallets.