VORTEX GENERATORS
These devices, which are usually installed on the upstream side of the mass airflow (MAF) sensor, use stationary vanes or, on some devices, spinning blades to make the inlet air between the air cleaner and intake manifold whirl around in a mini-tornado. This vortex supposedly mixes fuel more thoroughly with air, which means the fuel will, theoretically, burn more completely in the combustion chamber. Trouble is, there's a lot of intake tract downstream from these devices designed to maximize a smooth airflow. Turbulence, coupled with the restricted airflow caused by the device, can only reduce the amount of air sucked into the manifold. Less air means less power.

Again, we tested two devices. The TornadoFuelSaver is a nicely made stainless steel contraption, available in an assortment of sizes to fit most vehicles. We installed it on our truck's intake tract immediately upstream of the MAF sensor. We purchased the second device, the Intake Twister, on eBay. It was crudely handmade from sheet-aluminum flashing and pop rivets. It looked like something we could make in about 10 minutes from an old soda can. The staff at UTI was reluctant to install it: The bent sheetmetal vanes looked as if they might break off and be digested by the engine. The device is one-size-fits-all, and is simply bent into a curl to insert it into the intake duct.

THE DYNO SAYS: Both devices reduced peak horsepower by more than 10 percent. The Intake Twister increased fuel consumption by about 20 percent; the TornadoFuelSaver provided no significant change.