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Everything You Need to Know About S550 Mustang Diffusers

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One way to make your S550 Mustang stand out from the rest is by changing the exterior effects. Some mods like the chin spoilers and rear diffusers have performance benefits as well from better aerodynamics to better cooling from scoops.

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The 2015 Mustang brought a completely redesigned look to the iconic pony car and drastically altered the shape of the rear end. The rear diffuser of the S550 Mustang helped to tie together the whole look of the redesigned rear end. This guide will go over everything you need to know about S550 Mustang rear diffusers.

American Muscle

What Does a Mustang Rear Diffuser Do?

A Mustang rear diffuser helps to make the car more aerodynamic by smoothing the transition between the high-velocity airflow underneath your Mustang and the slower/stagnate free streaming flow of ambient air at the rear of the vehicle. A piece of the underbody that goes underneath the rear bumper helps to flow the air traveling under your car to the back. A rear diffuser helps to:

  • Allow your Mustang to travel with less air resistance 
  • Stay stable at higher speeds 
  • Improve your overall appearance.

Diffusers geared more for racing will use fins that help to channel and direct the air out the back.

Before and After Installation of a Rear Diffuser on a Premium S550 Mustang
Premium Package Rear Diffuser Before and After

What's the Difference Between Mustang Rear Diffusers & Valences?

It's common for people to treat rear valences and rear diffusers as the same part/mod, however they are actually two subtly different things. A rear valence covers the whole area underneath the rear bumper, stretching from exhaust opening to exhaust opening on each side of the car. A rear diffuser is only the section under the rear bumper right in the center; the rear diffuser stops where the exhaust comes out.

S550 Premium Mustang Carbon Fiber Rear Valence
OE-Type Carbon Fiber Rear Valence

Are EcoBoost, V6, & GT Rear Diffusers Interchangeable?

While the Mustang can easily share body parts amongst many of its sub-models, you may run into some issues trying to get a GT rear diffuser to fit on an EcoBoost Mustang. While some of the rear diffusers are able to be easily swapped across the different Mustang sub-models, it's really going to come down to what features your Mustang has.

Depending upon if you have the premium package, which uses a different style rear bumper, some of the diffusers may not work on your S550 Mustang. There are different rear diffusers cut for premium and non-premium Mustangs to accommodate for the different bumper designs. If you are unsure if you have a premium or non premium package on your Mustang you will either want to ask a Ford dealer to identify it for you or use a VIN decoder to determine what package you have.

If you are determined to make a premium specific rear diffuser work on your non-premium bumper, you can make it work with a good bit of custom fabrication. You will have to make use of a sawzall or some other type of cutting implement to get things cleared for fitment. In reality though, there are enough options available you won’t need to pursue an option like that; it would make more sense financially and stress wise to just get a diffuser that was made for your premium or non-premium equipped Mustang.

Carbon Fiber Rear Diffuser for GT and EcoBoost Mustangs
Rear Valence for Both GTs and EcoBoosts

Should I Upgrade My Mustang's Rear Valence Instead of Just the Diffuser?

This is a tough decision and one you should weigh carefully. Depending if you would like to go to a quad exhaust setup than you may want to consider going for a full rear valence since you can purchase one with a larger exhaust pipe opening

The decision to just upgrade your rear diffuser or your rear valence on your S550 Mustang is going to come down to you and what you plan on doing with the car. No matter what, you will be glad you made the mod and went for a more customized look for your Mustang.

Rear Diffuser Fins on a Non-Premium S550
Rear Diffuser Fin Add-Ons
Fitment includes: 2015, 2016, 2017, 2018, 2019, GT, V6, EcoBoost, ShelbyGT350