Throttle body spacers promise increased performance and improved fuel economy, but if you’re looking at what is essentially a small circular ring of metal and trying to figure out exactly how it’s capable of improving your engine, you’re not alone. Despite the fact that dynos and drivers both report seeing power improvements, it's tough to believe that throttle body spacers can be capable of that kind of improvement given their simple design. Understanding how these modifications function can help you determine whether or not it’s likely to improve your car meaningfully.
What’s a Throttle Body?
Before we can really get into the throttle body spacer, it’s important to understand what a throttle body does. Essentially, when you push down on the gas pedal in your car, the throttle body opens a valve, allowing air to enter the engine. In carbureted engines, the throttle body pressure creates a vacuum that releases fuel which mixes with the air in the throttle body.
On electronically fuel-injected engines, a sensor lets the “brain” of your car know how open the throttle is (which is dependent on how hard you’re pressing on the gas pedal) and based on that the injectors release more fuel. So, essentially the throttle body’s purpose is one of the most crucial in the continued functioning of your engine. Whether it’s a carbureted or fuel-injected engine, your throttle body permits air to enter and either via pressure vacuum or sensor, tells it how much fuel to inject.
Depending on your vehicle, the throttle body can look very different. Some vehicles have many throttle bodies or a throttle body with two valves. Most vehicles will have one large throttle body.
The Intake Manifold
Air flows through the throttle body and into the intake manifold, where it is distributed evenly to each of the combustion cylinders. This is where the air-fuel mixture is ignited, causing the explosion that moves the pistons and subsequently your car.
Though this seems simple, there are a few factors that help to explain how a throttle body spacer can be an effective tool for improving the power and fuel efficiency of your engine.
A high-pressure wave is formed when the intake valve closes, and that wave makes its way through the intake runners, away from the cylinder. Ideally, that wave will arrive back at the intake valve just in time for it to open again, but that doesn’t always happen. Variable intake manifolds exist for pretty much exactly this purpose, and by creating a separate pathway for fast-moving and slow-moving air are able to be more efficient than traditional intake manifolds.
Variable intake manifolds and throttle body spacers actually have a few similarities in that regard, including that some throttle body spacers claim to work by increasing turbulence. Fortunately, a throttle body spacer can have a similar effect without requiring a tune or anything more involved than dropping a single piece of metal in at the right location.
What’s a Throttle Body Spacer?
A throttle body spacer is a small metal circle that is installed in the place of the throttle body gasket, in-between the throttle body and the intake system. What this does is effectively lengthen the intake manifold, creating a small amount of extra space for air.
This extra space doesn’t amount to a lot of air, but what it also offers is a way to essentially create a small release for the high-pressure wave that comes through the intake runner, providing some of the same benefits that you would see from a variable intake runner without the same detriments.
Lengthening the intake manifold should absolutely improve your engine’s performance. More efficient air use means that there’s more power being produced and no additional energy being spent since a throttle body spacer is a passive device. Typically, users will see around five horsepower and ten pounds of torque improvement with the use of a throttle body spacer, though this number is going to vary significantly, obviously. While that might not sound like a lot, considering a throttle body spacer is literally a metal ring, it’s pretty impressive.
Different Shapes of Throttle Body Spacer
The different shapes of throttle body spacers are where the science starts to become a little more ambiguous. There are brands of throttle body spacer that promise to create a miniature hurricane inside of your intake manifold, essentially producing denser, more high-pressure air exactly where it can be used to produce more power. This is great, in theory, but whether or not that style of throttle body spacer works better than the ones that aim for the smoothest possible airflow is a matter of some debate.
There’s also an argument to be made for the turbulence being created via the spiral cut of these throttle body spacers working to more effectively mix the air and fuel in the combustion chamber, creating more efficient explosions.
Essentially, the people who are rooting for the hurricane are voting for the same technique of improvement as the people who prefer superchargers and hood scoops. Meanwhile, the people who prefer a smooth throttle body spacer are arguing for the same science as affects spoilers. Which camp you fall into ultimately depends on you, but it seems that for the most part well-constructed throttle body spacers have approximately equivalent results regardless of whether or not they offer an “unobstructed” pathway or the opportunity to create a “whirlwind.”
Who Are Throttle Body Spacers Right For?
The biggest factor affecting whether or not a throttle body spacer will offer premium performance improvements or only a slight change are what type of fuel injection system your Mustang has. Vehicles that operate carburetors or those with fuel injection systems that mix the fuel and air in the throttle body are the ones that saw the most performance gains. Once you get to a multi-port fuel injection system the gains were more minimal since the fuel/air balance was already closer to optimal.
There’s additional evidence to support the theory that the actual reason throttle body spacers work is related more closely to intake plenum volume. Because auto manufacturers tend to use similar parts for different engines, it’s likely that the intake plenums in your car are designed in a medium ground that can work with both the low powered four-cylinder engines as well as the higher-powered V8s. This means that the high powered engines are being choked, which is exactly what it sounds like. Without adequate air supply, the engine is trying to breathe and having the same problem as a runner in a too-tight shirt, they’re not getting enough oxygen and need a little extra room to expand. On the other hand, if you’re the person in the four-cylinder, a throttle body spacer is unlikely to help you.
Throttle Body Spacer Pros and Cons
Ultimately, a throttle body spacer isn’t a “must-have,” but the science certainly does show that some people are getting improved performance from nothing more complex than a metal ring, which is appealing.
Throttle body spacers are an inexpensive, easy to install modification that has consistently been shown to deliver a very small but very real horsepower and torque boost in addition to a minor fuel economy one. If you’re running a smaller engine you may notice a reduction in low-end torque, and some people have had to adjust their intake runner length to accommodate the part, but, for the most part, it’s a pain-free install.
In this video, Bill shows us how to install a throttle body spacer.
Additionally, while most modifications require a tune to really be efficient, a throttle body spacer does not, although it can be a part of a larger modification, which may need a tune.
One strategy, if you’re still unsure, is to ask other people with the same model of car who have installed a throttle body spacer if they’ve noticed any performance boost. This can help you assess if your individual model will be helped by a throttle body spacer since the performance difference can vary based on aspects like how well a car’s engine already “breathes.”
Image Credit: Mazda Repair Guide