Fox Body Mustang Throttle Body Selection Guide

Which Throttle Body is right for your Fox Body?

We’ve all been there. Every single one of us who own a 79-93 Mustang, you start to get that itch. You know, that one where you want to make your Fox go faster, sound meaner, handle better, or look cleaner. If you are like me, you already know that going faster is always the way to go.

The problem always seems to be choosing a part that not only stays within your budget, but ultimately gives you the most bang for your buck. For a lot of people, upgrading the Throttle Body is a budget-friendly, and easy-to-install mod for your 5.0.

What is a Throttle Body?

The Webster’s Dictionary describes the Throttle body as “A part of the air intake system of a fuel injected engine, responsible for regulating the airflow into the engine.” This description could not be more accurate. Ford equipped the 1986-1993 Mustangs with a 57 millimeter throttle body from the factory. That size of throttle body was not very friendly to the wave of performance modifications that were, and still are, available to the 302 based fox.

The reason why people swap out the throttle body is two fold. Better throttle response, and better airflow to support modifications. The latter is the biggest thing to remember, especially when considering potential head, cam and intake purchases. A throttle body by itself will not increase horsepower, but rather work in conjunction with other mods to increase horsepower.

So in short, the sole purpose of the Throttle Body is to allow air to enter the intake, in direct relation to how hard you press the gas pedal. The harder you press the gas, the more air is allowed to enter the combustion cycle, and the faster you go. Sounds pretty simple right? Not exactly.

The Science Behind the correct Throttle Body

Believe it or not, There actually is a science behind choosing the correct throttle body. Bigger is not always better when it comes to throttle bodies. I know what you may be thinking. And it all boils down to two words: Venturi Effect.

The Venturi Effect is when a fluid (air) enters a funnel the velocity of the fluid increases as the cross sectional area decreases, with the static pressure correspondingly decreasing. According to the laws governing fluid dynamics, a fluid's velocity must increase as it passes through a constriction to satisfy the principle of continuity, while its pressure must decrease to satisfy the principle of conservation of mechanical energy. Thus any gain in kinetic energy a fluid may accrue due to its increased velocity through a constriction is negated by a drop in pressure (http://en.wikipedia.org/wiki/Venturi_effect).

Basically, in layman's terms that means that the more volume of air that you can tunnel through your air intake, the higher velocity it will be as it goes into your intake manifold. This effect is easily achieved by purchasing a quality cold air intake that starts large at the inlet, and tapers down smaller into the throttle body. This is especially important when it comes to forced induction. The more air you can move, the better your engine can breathe. That means more horsepower, and more torque.

The most common problem that some people run into with their throttle bodies is the fact that they go too big for their specific application. Too big of a throttle body will actually decrease throttle response, and decrease the desired Venturi Effect you are looking to create.

So, which Throttle Body should I choose?

Just like anything else in life, there are plenty of throttle body choices to choose from. The most common throttle bodies are 65 mm, 70 mm, 75 mm, and 90 mm. All of which have a specific application that they would correspond to.

• 65 and 70 mm throttle bodies are great choices for naturally aspirated, stock displacement engines.
• 75 mm throttle bodies are a great choice for larger displacement engines, and forced induction applications.
• 90 mm throttle bodies are a great choice for larger displacement engines, with high levels of boost from a forced induction application.

Once you understand the simple concept of what a throttle body is, and what it does, selecting the correct one for your car should be a walk in the park. Now that you understand that, let’s wrap our head around some of the parts that make the throttle body more effective.

EGR Spacers and Cold Air Intakes

EGR Spacers are also on the same level of misunderstanding as the throttle bodies. Anyone that has ever spent any time underneath the hood of a fox installing go-fast parts, knows about the importance of an EGR Spacer. The problem is, nobody seems to know why they are important. The purpose of an EGR Spacer, is to aid in the warming of the car in colder climates. It also helps funnel air into the throttle body. It also acts as a mounting point for your throttle linkages.

Much like the throttle body, they come in various sizes. 65, 70,and 75 mm are the main choices for the EGR Spacer. The ideal EGR Spacer will match the size of the throttle body, as anything smaller will act as a minor restriction, and anything larger will only flow what the throttle body can handle.

The Cold Air Intake plays a pretty big part in all of this airflow business too. Like I outlined earlier, a good cold air intake will always be wider at the Filter/MAF location, and taper down in size, forcing the air to essentially ram itself into the throttle body. It also helps expound the impact of your throttle body/EGR Spacer combo.

You would always want to consider purchasing the EGR Spacer Plate when you purchase a throttle body to maximize the performance gains that the increased airflow has to offer. Especially if you are considering going with an aftermarket heads, cam, and intake combo.

Considering all of the science, and everything that I’ve laid out for you, a Throttle Body/EGR Spacer combo is a fun, easy, and budget friendly way to bolt on some additional performance to your 1986-1993 5.0 Mustang!