Jeep Throttle Body Spacer Review: Do They Actually Work?

A throttle body spacer is a machined aluminum or plastic block that bolts between the throttle body and the intake manifold, increasing the volume of the intake plenum. Some spacers feature internal spiral grooves, helix patterns, or vaned channels that claim to create a swirling effect in the incoming air charge. The theory is that this swirl promotes better air-fuel mixing in the combustion chamber, resulting in more efficient combustion and therefore more power and better fuel economy.

Throttle body spacers have been around for decades and are marketed for everything from Jeep Wranglers to full-size trucks. They typically cost $50 to $150 and can be installed in 20 minutes with basic hand tools. The installation involves removing the throttle body from the intake manifold, placing the spacer in between, and reinstalling the throttle body with longer bolts (usually included in the kit).

Companies like Airaid, BBK, and Volant claim their throttle body spacers can add 5 to 25 horsepower and 5 to 25 lb-ft of torque, along with improvements in fuel economy of 1 to 2 MPG. These claims are typically accompanied by proprietary dyno charts that show peak power gains in specific RPM ranges.

The proposed mechanism is that the increased plenum volume and air swirl improve the volumetric efficiency of the engine, allowing more complete combustion of the air-fuel mixture. On older carbureted and throttle-body-injected engines, there was some validity to this concept because fuel mixing was less precise and occurred further from the combustion chamber. On modern multi-port and direct-injected engines, however, the fuel injectors spray directly into the intake port or combustion chamber, making intake plenum swirl largely irrelevant to mixture quality.

When independent testers put throttle body spacers on a chassis dynamometer with controlled conditions, the results are consistently underwhelming. Multiple independent tests on the 3.6L Pentastar and 3.8L V6 Jeep engines have shown gains of 0 to 3 horsepower, which falls within the margin of error for most dynos (typically plus or minus 2 to 3 percent). The fuel economy claims are similarly difficult to verify, with most controlled tests showing no statistically significant improvement.

The reason is straightforward engineering. On a modern fuel-injected engine, the throttle body is not the flow restriction. The factory throttle body on a 3.6L Pentastar flows far more air than the engine can consume at any RPM, and the intake manifold is already designed with runner lengths and plenum volumes optimized for the engine's displacement and operating range. Adding a one-inch spacer between the throttle body and manifold does not meaningfully change the intake dynamics.

Where throttle body spacers do show measurable (if small) results is on older engines with restrictive intake manifolds, particularly the AMC 4.0L inline-six found in TJ Wranglers and XJ Cherokees. The 4.0L's intake manifold is a known restriction point, and the slightly increased plenum volume from a spacer can produce gains of 3 to 5 horsepower in the mid-range RPM band. This is a real but modest improvement.

For the 3.6L Pentastar, 2.0L turbo, or any modern fuel-injected Jeep engine, a throttle body spacer is not a recommended performance upgrade. The money is better spent on a cold air intake, exhaust upgrade, or tuner, all of which produce verifiable, repeatable gains on a dynamometer.

For the 4.0L inline-six, a throttle body spacer is a marginal but real upgrade that can complement other intake modifications. If you already have a cold air intake and are looking for every last bit of improvement from the intake side, a spacer is a low-cost addition that may add a few horsepower in the mid-range.

The best use case for a throttle body spacer on any engine is as a heat insulator. The aluminum or phenolic spacer material creates a thermal barrier between the hot intake manifold and the throttle body, which can reduce intake air temperatures by 5 to 15 degrees. Cooler intake air is denser and does produce a small power benefit, though this effect is more pronounced in hot climates and on engines that suffer from heat soak.