Approximate Gains: 5 to 45 percent (see above)
Works on: Gas- and diesel-powered vehicles
What is it: Walker Engineering Enterprises of San Fernando, California, basically leased the rights to the patented technology that Advanced Power Systems International developed for the Fitch Fuel Catalyst. In other words, the Walker Fuel Sep is the same as a Fitch unit. Walker just packages them differently and with an emphasis on marine applications.
The most significant thing you can do to improve fuel economy is drive smarter. Think of your gas pedal as a fuel flow valve. Cranking that valve wide open results in fast acceleration, but in many cases it doesn't propel the vehicle much faster than 31/44 throttle would. Try it yourself-you may find that your vehicle has a similar response. When we try to save gas, we act as if the gas pedal has little Peggy's lost Easter egg underneath it, driving at as low an rpm as we possibly can.
Approximate Gains: 5 to 45 percent, depending on vehicle
Works on: Gas- and diesel-powered vehicles
What is it: The Fitch Fuel Catalyst is a maintenance-free device that easily installs in the fuel line, much like a fuel filter. Think of the Fitch as a finish-polisher before fuel reaches the combustion chamber. We like the Fitch because it lets you run 87-octane gas on a vehicle designed for 92 octane. This saves you money immediately at the pump. On our '05 Jeep Liberty CRD, we found it increased economy by 1.2 mpg on average.
Approximate Gains: 3 to 30 percent, depending on gear ratios
Works on: Gas- and diesel-powered vehicles
What is it: Gear Vendors Overdrive units are basically a planetary gear cluster that bolt on behind the transmission. They are designed to be used in two-wheel drive and can be shifted under any throttle condition. We like them because they let you shift up or down just half a gear at a time. These units have traditionally been reserved for heavy-duty towing applications where power and economy go hand and hand. However, an auxiliary overdrive, or "gear splitter" as some call them, can actually shave a sizable chunk off your annual fuel bill unloaded. The reason: A gear splitter doubles your available gear ratios. For example, imagine your engine requires one gallon of fuel at 60 mph in overdrive to take you 15.5 miles. With a Gear Vendors Overdrive unit installed and with the double overdrive gear selected, you could theoretically go 20 miles on that same gallon of fuel. Simple gearing allows the engine to work less to cover the same distance.
Approximate Gains: 1.1 mpg
Works on: Gas- and diesel-powered vehicles
What is it: Electric Fan Conversion Everyone knows crank-driven fans rob engine power, and that's why Flex-a-lite offers several electric fan conversion kits for popular diesel-powered pickup trucks. The one shown here is for '01-'05 Chevy/GMC Duramax Diesels (PN 284). What this does is eliminate the power-robbing beltdriven fan and shroud, replacing them with an electric fan to improve mileage, horsepower, torque, and air-conditioning temperature.Independent dyno tests have shown a fuel savings of 1.1 mpg with a 27 hp and 34 lb-ft of torque increase at the wheels with this kit.
Approximate Gains: .5 to 1.5 mpg
Works on: Gas- and diesel-powered vehicles
What is it: The Turbo Air Guide (TAG) is a simple device invented by a company called Diesel Power Products of Pasco, Washington. Designed to be used in conjunction with any turbocharger, the TAG helps get more air smoothly into the compressor housing. The TAG straightens air out and directs it into the compressor of the turbo, resulting in more power, cleaner burning and better mileage. It is constructed of a stainless steel welded honeycomb material and is easily installed in the turbo inlet on most popular American diesel pickups. We tested a TAG on our own Baja Bomber project truck and noticed a very slight increase in economy in stock form.