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Throttle-Body Spacers

An easy way to add 4-12 horsepower

Many mechanics consider throttle-body fuel injection to be simply a computerized carburetor. Unlike the more-sophisticated multiport-injection (MPI) setups (which squirt fuel directly into the combustion cylinder), throttle-body injection (TBI) pulsates gas into the intake manifold and lets the fuel get sucked into the cylinders. Because TBI is less precise than MPI, same-sized engines that have the cruder of the two systems usually produce less power. The good news is that the automotive aftermarket offers a few at-home tricks for increasing TBI power.

Spacers

Most people know that colder weather makes things contract. The colder gas is when it enters the combustion chamber, the more air can be added to it to create a bigger explosion, which generates more power. In many cases, longer pathways permit greater heat dissipation. This is the theory behind aftermarket throttle-body spacers: increase the distance the fuel travels by spacing the injector farther away from the intake manifold.

A variety of engine-performance-parts manufacturers make spacers for popular TBI engines. Common thicknesses are 3/8- and 1/2-inch (depending on hood clearance), and TBI spacers are usually made of either aluminum or a composite material. Manufacturer-estimate power gains from a TBI spacer alone range from 4 to 12 horsepower, depending on engine size and condition.

Install

Putting in a TBI spacer can be easy, particularly if your engine compartment allows easy access to the throttle body. First, play it safe by relieving the pressure from the fuel system (consult a service manual), then disconnect the battery's negative cable. The throttle body must be lifted so that the spacer can be sandwiched between it and the intake manifold. The step-by-step photos here show highlights of the job on a TBI Chevy 350/5.7L V-8.

Best of all, this performance modification normally doesn't require any special tools or uncommon mechanical abilities. Finally, most reputable manufacturers verify that their throttle-body spacers are compatible with the vehicle's computer. Afterward, the "brain" should sense more/denser fuel and match it with more air. More power is the end result.