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When and How Should I Upgrade My Throttle Body?

Written By: Gin Yum

Throttle bodies in the era of carbureted engines were designed to allow for more time for fuel and air mix together. Nowadays things are more advanced, but be it for race, drag, or daily driving, the concept behind them and their benefits remain the same. A throttle body might seem like a minor mod in relation to the broad scope of the rest of the engine. However, a throttle body is a great compliment to a high horsepower engine as well as a lightly modified build.

American Muscle

How Throttle Bodies Compliment Power

First and foremost, upgrading the throttle body on any Mustang is considered a supporting modification. What this means is a throttle body on its own will not add a whole bunch of juice by swapping it. Rather, the throttle body supports horsepower. It is a fundamental piece to making power, but does not make power on its own. A properly sized throttle body will provide sufficient air flow and velocity for good engine power and throttle response. Essentially, it allows horsepower to flow through it. With this in mind, why might someone want to change it, and when is a good time to do so?

2015-2016 GT350 Mustang 87mm Throttle Body
GT350 87mm Throttle Body

Why You Should Consider Changing Your Throttle Body

  • Supports high horsepower builds by reducing air restrictions
  • Improves throttle response to help wake up the engine
  • Older Mustangs can have carbon buildup, restricting air flow and making the throttle body stick

Mathematically speaking, if you were to swap your stock throttle body for an aftermarket unit and strap your Mustang to a dyno there likely would be a power difference. Sadly, this difference will most likely be in the neighborhood of a couple horsepower – not enough to register an increased seat-of-the-pant feeling. For this reason, throttle bodies are not considered to add power. Also if your install too big of a throttle body, you can reduce your Mustang’s power.

Upgraded BBK Throttle Body vs. Stock
Stock vs. upgraded Throttle Body

Well, if they don’t add power what good are they? As stated earlier, they support power. This in itself is a pretty boring statement. It is important, but not particularly exciting. Again it isn’t something the driver can feel. What the driver can feel, however, is throttle response. Aftermarket throttle bodies are designed in such a fashion to not only support large numbers of horsepower, but to increase throttle response as well. Less restriction through the throttle body in combination with polished surfaces help cut down on any lag time for the air to get moving when the accelerator is depressed.

82mm Mustang Throttle Body
82mm Throttle Body

When Should I Upgrade?

This is a very good question, and there isn’t a hard line or clear cut methodology to answer it. Changing the stock throttle body for an upgraded version can be done right away, or it's something that can be put on the backburner until a major engine upgrade comes around. It's very subjective.

Swapping the piece right away will positively impact throttle response which is felt instantaneously. Even if your Mustang isn’t making any extra power at the moment, the increased throttle response is beneficial nonetheless. Basically, adding an aftermarket throttle body before you even need it won't harm performance. For this reason, it's recommended to acquire one earlier rather than later.

2009 GT500 Shelby Mustang on a Dyno

Standard procedure for the old pushrod 5.0L V8’s was to acquire all of the supporting mods first and then jump into the engine. It's no fun building a 500 horsepower engine, and then realize you're restricting power because of one forgotten part. For most Coyote owners, the primary advantage of an aftermarket throttle body is the increased throttle response. The capacity to support larger horsepower is a bonus should you wish to slap on a supercharger, or another adder, later down the road. On the other hand if your engine is already modified, the primary advantage is not impeding performance, and throttle response becomes a secondary benefit.

2010-2014 Mustang with a Centrifugal Supercharger

Don't Go Bigger Than You Need

  • Mildly modified/stock Mustangs do not have enough air flow to fully benefit from the largest throttle body, and consequently, can reduce throttle response
  • Trying to push too much air flow without the fuel to compliment it could risk damaging your engine

If your Mustang is stock or mildly modified, your engine doesn’t flow enough air to fully benefit from the largest throttle body available and can consequently hurt your throttle response. Think of mild mods as a cold air intake, a cat-back, or an axle-back exhaust. You'll need further fuel modifications to compensate for the added air the largest throttle bodies can offer. Running too lean can damage your engine.

BAMA Tuner with a BBK Mustang Cold Air Intake

For example: take a 1996-2004 naturally aspirated GT with an intake and an aftermarket exhaust. The 70mm throttle body would be the best option for HP and throttle response gains. A 78mm would be too excessive and cause lean air/fuel mixtures. Even if you plan to add several additional bolt-on mods, the 70mm would be plenty big enough. It’s larger than stock to increase air flow over the stock restrictive unit, yet not too large that it results in lost velocity and ultimately decrease mid-range rpm gains.

Moving away from the 4.6L engine, if you are driving a naturally aspirated 5.0L with some mods, moving up to a 90mm throttle body would be a solid choice for improved power and performance. A 90mm throttle body is a great step up from stock, giving both naturally aspirated and forced induction motors a healthy dose of air, helping to give you a strong power band.

70mm Throttle Body on a 1996-2004 Mustang GT
70mm Throttle Body on a 1996-2004 GT

If you have a heavily modified Mustang (forced induction or extensive head work, anything that makes significant changes in air flow), then a 75mm throttle body or larger would be your best bet. A BBK 78mm throttle body is one of the most popular options. It incorporates a high flow intake plenum and is a great combo to compensate for the increased air flow from the engine. Just don't forget to add fuel injectors and perhaps a boost-a-pump for all that extra, supercharged air.

Stock Mustang Throttle Body Sizes

YearThrottle Body Sizes
1979-199358mm
1994-199560mm
1996-2004 GTs65mm (The 1999 2V GT has a 66.8mm)
1999-2004V6: 56mm, Cobras: Twin 57mm
2005-2009Twin 55mm
2010-201680mm

How do I Check the Size of My Throttle Body?

The easiest way to measure a throttle body size is to measure across the inlet for the diameter. On a twin application, this would be the widest point. Using a tool like a dial caliper is the most accurate way to take this measurement.

What are Competition Style Throttle Bodies?

  • Competition style throttle bodies feature no hose fittings or factory hook-ups, simplifying the throttle body's role
  • On a stock setup, with the computer trying to make too many changes, your Mustang will be slowed down in an attempt to keep everything safe

When you look at most street driven cars, attached to the throttle body are several coolant or air/vacuum lines and hoses running to and from it. This is a way for the car to gain more information on the air temp, the amount of air passing through and what position the throttle is at. However, on some vehicles that are heavily modded, or using forced induction, this can be a problem.

Too much information on a vehicle that needs a relatively specific and consistent air/fuel ratio or that is intentionally being set up super rich/lean for racing may cause issues. Also, when converting from fuel injection to a carburetor set up, there is no need for the extra hoses and their feedback. So, what to do? Scrap your factory throttle body for a competition style.

SR Performance 70mm One Piece Throttle Body for 1996-2004 GT Mustangs
70mm One Piece Throttle Body for 1996-2004 GTs

How Does a Competition Style Throttle Body Work?

A comp throttle body can be beneficial mostly in high HP applications. Not only can it simplify the vacuum system by not requiring hoses, but also has a higher chance of proper performance as a result. It can also become easier to tune as a result of no hoses. A competition style throttle body operates in the same manner as stock throttle bodies and installs generally in the exact same way. With a spring loaded, cable driven side car attachment (for Mustangs) for cruise control and throttle cables it still bolts right to the intake so you do not need special tools. However since it won't have any of the attached hose fittings or factory hook ups, you’ll need to plug the exposed spots. This will keep the information relayed to the computer (if still fuel injected) or make the set-up of a carburetor much easier, especially on supercharged and turbo style cars.

Accufab Oval Style Throttle Body and Plenum Combo Installed on a Supercharged 2003-2004 Mustang Cobra
Oval Style Throttle Body and Plenum Combo Installed on a 2003-2004 Cobra

A Mustang's Computer - Tune Required Throttle Bodies

As far as competition style throttle bodies go, the computer is trying to make too many changes, and will slow the car down in an attempt to keep everything “safe.” The computer will try getting as close as it can to meeting the load demand as if a stock throttle body is left on. A competition style throttle body is not intended as a bolt-on due to the new tune that is always going to be required.

Mods that Benefit from a Mustang Throttle Body

A throttle body is a fantastic support modification. What this means is by itself, it won't provide the most benefit. However, when other modifications are added, a throttle body will shine more and more. Great modifications that pair with a throttle body include cold air intakes, intake manifold, headers, and CMCV or (CMDP depending on the year) plates. These all allow for the air being pumped in and out to have more flow and less restriction. Continue reading to see the benefits of a throttle body spacer.

2005-2008 Mustang GT with Steeda Billet Charge Motion Control Plates Installed
2005-2008 GT with Charge Motion Control Plates Installed

Why Get a Throttle Body Spacer?

  • Use a spacer to make room for other mods
  • Boost your horsepower, mpg, and throttle response
  • The threaded/spiraling variety help mix incoming air and fuel
  • Easy mod for a beginning enthusiast
  • Paired with further intake mods and a tune could provide an even bigger bump in horsepower

One use for an aftermarket throttle body is for space requirements, be it to adjust the position of your throttle body or other intake components. In a Mustang designed for track-only or performance purposes, you may choose to delete your EGR (exhaust gas recirculation), which requires specific throttle body spacers on foxbody Mustangs. A throttle body spacer can be an additional or required part for an upgraded induction and throttle system.

1998 GT Mustang EGR System
1998 GT EGR System

Will a Throttle Body Spacer Increase Horsepower?

Gains from a throttle body can be dependent on modifications. Generally speaking, anytime a throttle body is added, there will be some added horsepower. The amounts can range from 5-25 HP depending on what other modifications are done to the engine. In stock form, the gains will be on the smaller side of that range while a heavily boosted mustang will see gains on the higher side of that range. A throttle body spacer is more of an aesthetic and sound mod. One of the most common reasons Mustang owners install a throttle body spacer is for better gas mileage and throttle response.

Throttle Body Spacer Installed on a Mustang

How Does a Throttle Body Spacer Work?

The throttle body spacer is based on the theory that air entering a chamber will have a greater velocity and more mass if spun. The helical groves on the throttle body spacer are designed to make the air spin, thus delivering a greater volume of air to the engines cylinder. This in turn, increases the power of detonation by adding more air to the fuel/air mixture. Additionally, on older model Mustangs with throttle body injection, the swirling air mixes the air and fuel much better, providing a more consistent spark and hotter detonation. More air & a stronger detonation = more power.

There are a few downsides to a spacer. The largest issue is it does not add large amounts of power in most situations. Having a spacer on, while not in all cases, can lead to fitment issues with other parts. It also is more succeptible for leaking and (while a small amount) does add weight to the car itself.

Does a Throttle Body Spacer Require a Tune?

If you’re just installing a throttle body spacer by itself, then a tune is not necessary. On the other hand if you’re installing this spacer along with a new throttle body or intake or any related parts then a tune is always recommended to receive the most possible gains from your modifications.

BAMA Flash Tuner Loading Up on a 2015-2017 Mustang GT
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