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How to Delete the Catalytic Converters on an S550 Mustang

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If you're looking to make your new Mustang a track only beast, deleting the cats is a must. Unfortunately, Ford decided to make the S550 a bit more special than other Mustangs. Swapping out your cats for off-road pipes is more complicated than later gens.

The Basics

  • Catalytic converters are required on all road going vehicles, and are essential to passing emission testing
  • “Off-road” systems do not use catalytic converters. They are “strictly” sold for non-road going vehicles only
  • An “off-road” system is less restrictive, but more pollutant and may produce nauseating odors

Benefits to Deleting The Catalytic Converters

Catalytic converters are great - yeah, they really are. They filter out a lot of harmful contaminants that would otherwise pollute the air we breathe. Though, if laws and regulations don’t apply, the removal of them can be a pretty good idea, in the name of speed. What would any gearhead rather? Fresh air or horsepower? 

In order to meet federal emissions standards, cars have to have catalytic converters on them. These are a honeycomb of different substrates welded into the exhaust. As you can imagine, having a densely packed honeycomb in your exhaust is going to restrict the flow and hurt your power. A quick and easy mod for Mustang owners is to install an off-road mid-pipe on their pony. The off-road mid-pipe gets rid of the cats and improves exhaust flow, which leads to an increase in horsepower and torque. Unfortunately for some S550 owners, it is not as quick and easy to delete the cats.

S550 BBK Cat Delete Pipes

Pre ’15 Exhaust Compared to 2015

The 79-14 Mustang exhaust system is has exhaust manifolds coming off of the engine, which are then bolted to a mid-pipe that contains the cats, followed by a catback. This modular exhaust set up made it very simple to swap out mid pipes, headers, and catbacks. The exhaust set up on the 2015 GT and EcoBoost engines are little bit different from the earlier Mustangs. The V6 however, is set up the same as the 79-14 Mustangs, but there no mid-pipes available for the V6.

Mustang Long Tube Headers

Helping Your EcoBoost Breathe

That EcoBoost Mustang may be making some pretty decent power, but the catalytic converters are strangling it. Deleting it will increase the flow of exhaust, which means gains in both power and efficiency. How do you delete one? In comparison to GTs and V6s, EcoBoost owners are sitting pretty. With about an hours work you can quickly and easily remove the stock catalytic converter, freeing up some horsepower. Since the EcoBoost is turbocharged, removing the catalytic converter will give you a huge boost in power!

Well, to just remove the cats would leave the exhaust wide open. Something needs to go in their place. With EcoBoost engines, the cats are right off the downpipe. Rather than trying to find the right piece to bolt in the void between the downpipe and the rest of the exhaust system, extended downpipes can be purchased to fill the gap. This makes life a lot easier for those looking to free up some ponies. Though, we must revisit the fact that this modification is intended only for track applications, not for street cars.

Borla Ecoboost O/R Downpipe

Uncorking Your GT’s Exhaust

The exhaust on the 2015 GT makes it a little tricky to delete the catalytic converters. Unlike the previous generations of Mustangs, the catalytic converter on the driver’s side is integrated with the exhaust manifold, meaning it can not be unbolted easily. Deleting the cats on a GT will either require removing and replacing the stock exhaust manifolds with a set that does not have catalytic converters, or cutting the converters out and having new pipe welded in place. Having the converters cut out would most likely also require removal of the drivers side manifold. The good news is that it is a perfect excuse to upgrade to a set of long tube headers!

Deleting Your Cats Will Give You:

  • Better exhaust flow
  • Increased horsepower and torque 
  • Louder exhaust volume
  • Weight savings from removing the heavy cats

GT owners got dealt a raw deal on the 2015 Mustang when it comes to easily removing the catalytic converters. While this may be disappointing to many Mustang GT owners, installing a set of long tube headers and deleting the cats at the same time will give you amazing boost in power. When paired up with a new catback, you will have a very mean sounding Mustang with a very free-flowing exhaust. EcoBoost owners can take advantage of the easy-to-swap down pipe for an increase in horsepower and torque. Unfortunately, V6 owners will have to sit tight until aftermarket support catches up with them.

Long Tube Headers - Updated and Meaner Than Ever

Aftermarket long tube headers for S550 GT Mustangs are now much different than what has been seen in the past. The catalytic converters are now incorporated into one piece with the headers, making for one mean looking pipe.

These converters are there to scrub the exhaust as it flows to the tail pipes, eliminating toxins and harmful pollutants (rather, converting into less harmful pollutants). Aftermarket long tube headers will incorporate high flow cats that offer less restriction than stock, but still maintain the stringent emissions standards that are being more and more commonplace. Unfortunately, due to the presence of the catalytic converts, the price of this style header is up there.

Off-Road Headers - For Power and Sound

Off-road headers, on the other hand, are like the headers of the old days. They have the primary tubes that flow into the collector, and the collectors connect to the rest of the system. No catalytic converters involved. In terms of overall performance, these off-road pipes are second to none.

Despite the high flow cats being used on today’s S550 headers, they still impose some restriction on the exhaust. Having no converters of course has zero impedance! The downside is that these pipes are called “off-road” as, in many places, they are not legal for regular street use.

If emission checks are standard practice in your region, you can forget about running an off-road pipe. There is no way the Mustang will pass. Furthermore, catalytic converts also remove the smell of the exhaust (gas fumes, in particular). Running without cats can make for a very stinky, even nauseating ride!

Overall, in today’s day and age, off-road pipes just don’t have the place they used to. Modern converter systems are pretty efficient, and don’t pose a major restriction for a regular street car.

Furthermore, as more and more areas are cracking down on emissions and exhaust noise, cat-less systems are just not feasible.  If you’re looking for absolutely as much power as possible, off-road is the way to go. Otherwise, stick with catted headers. They are well worth the small decrease in performance.

Cat-back System - Mid-Piping to the Tail

The rest of the exhaust, rear of the headers, is often described simply by the words ‘cat-back’, as in rearward of the catalytic converters. For 2015 Mustangs, this simply consists of the intermediate piping from the headers to the mufflers and then the tail pipes.

In this case, on-road and off-road catback systems usually differ by the type of muffler, or perhaps the presence altogether of a muffler.

100% street legal systems will incorporate baffled mufflers. A baffled muffler is an additional method or muffling the engine. Not to say that baffled catback systems are quiet (they can still be very loud), they are just quieter when compared to a straight-through muffler design.

Off-Road Cat-backs - For the Track Beasts

Off-road cat-back systems will use straight-through mufflers, resonators in place of mufflers, or perhaps no muffler at all. From an emissions standpoint, mufflers are not important. From a noise standpoint, however, mufflers are critical.

And like many regions are cracking down on emissions, many communities are going after exhaust noise too. In some areas, straight-through mufflers are not street legal and can earn their owner a nice ticket if a police officer happens to notice. How do the police test for a straight-through muffler? Simple, they try and pass a small metal rod through it. If the rod can go through unobstructed, the muffler is not baffled.

Those systems without mufflers at all, despite their ferocious sound and minimal restriction, are not legal anywhere. At least for street registered Mustangs.

Axle Back System - Quicker Sound Modifier

Axle back exhaust kits are solely the muffler and tail pipe portion of the exhaust. They do not come with any piping further upstream than the mufflers. These kits follow the same principles as the cat-back systems – they have baffled or straight-through muffler designs.

Baffled systems, being somewhat quieter (and legal) pose a bit more restriction. Straight-through mufflers, posing minimal restriction but greater noise, may get you in trouble with the police. Buyer beware.

Fitment includes: 2015, 2016, 2017, 2018, 2019, GT, V6, EcoBoost, ShelbyGT350