Dual Exhaust - 5.0L V8

For All 5.0L V8 1983-88 Cougars / Thunderbirds

Page Revised: 10 May 2019


Article by
Eric Dess

Somewhere it's an unwritten rule that if you have a rear-drive V8 American car, it must have dual exhaust. That's just the way it is. So if you've got a 5.0 engine in your Cat or 'Bird, you're probably thinking about putting a dual exhaust setup on the car. Considering that our car is generally a big Mustang, it would make sense that a Mustang-type dual exhaust will fit on the Cougar, right? Well, yes; in fact, you can use the entire system on the Cat with a few minor tweaks here and there. Rest assured, no matter what anyone else tells you, you WILL be able to put dual exhaust on your Cougar.

But where to start? Should you go with a stock Mustang system? Or what about the off-road and high-flow H-pipes? Or the newer X-pipes? Or should you just have a custom system bent for the car? These are some serious questions that you have to figure out on your end. Once you do, read on below to see what you're getting into first. Whether you're on a budget, or want the absolute best, or want to strike a happy medium, there's a section below that will fill your needs.

Before you haul off to buy parts, there are a few things you need to understand about your car first:

Double Hump Transmission Crossmember

A lot of Cougars and Thunderbirds from 1983-88 have the "double-hump" transmission crossmember from the factory. This crossmember is so named because it has the two humps necessary to clear a dual exhaust system. Some cars only had the single crossmember, meaning it won't work with duals. Be sure to crawl under your car and check the passenger side of the crossmember to be sure that it's got the hump and is not flat. Should you need to purchase a dual-hump trans crossmember, any 5.0L V8 Mustang from 1986-93 can provide one. Additionally, Ford Racing does sell them new (p/n M-5059-A) and you can purchase one through Jeg's or Summit Racing.

Thanks to Sean for the part number.


Since no 1983-86 car ever left the factory with duals, there are a few anomalies with putting duals on that body style. The fuel filter (and depending on the model year, the external fuel pump) is located on the rear frame rail, passenger side, right in front of the rear axle. Exactly the spot where the passenger muffler goes, naturally. So you'll need to a) reroute the filter and/or pump, b) run a skinny muffler, or c) live with the passenger muffler hanging down lower than the driver's side. You will need to crawl under your car and determine the best course of action.

Some people have converted 1983-84 cars from a dual fuel pump (lower pressure inline "puller"/higher pressure in-tank "pusher") configuration to a single high pressure in-tank pump setup, similar to those used on 1985-88 cars; this will help get rid of the obtrusive external pump and allow plenty of clearance for the passenger side muffler. However, if you don't want to do all of that work (and believe us, a fuel tank change is not fun) then you can either use a very skinny muffler or dump the exhaust in front of the rear tires. There's very little room for clearance over there so caution is a must.

In moving the fuel filter on 1985-86 cars, it is perfectly fine to simply move it up toward the front of the car, about 6"-8". This will allow clearance for the passenger side muffler. While the muffler is still a really tight fit, it helps out very much indeed. Or, you can relocate the fuel filter outside the subframe rail with relative ease—there's usually enough slack in the fuel line there to do it.

Additionally, there are no factory hangers for the muffler or the tailpipe on the passenger side. You can use stock Mustang or 1988 V8 Cougar/Thunderbird hangers, if you wish. Problem is, if your new exhaust kit comes with the hangers pre-welded onto the tailpipes, the hanger will hit the fuel filler neck on the passenger side. Not a good thing; in fact, it's extremely dangerous. This will necessitate having the tailpipes lengthened to clear the filler neck. But then where do you hang them? We've used universal hangers with fair success. With a little creativity you can come up with something.

Finally, you will need to take special precautions to make sure that a passenger side muffler will not burn a hole in your lines, filter, or the fuel pump housing. Header wrap or other high-temp foil padding are highly recommended!


For the 1987-88 Cougars, Ford did some rerouting of the brake and fuel lines, as well as a relocation of the fuel filter to the outside of the framerail, so putting in duals is a lot easier. Provisions for dual exhaust were built into this body style. If you've got an '88 with the factory duals, and are ditching the split Y-pipe for an H- or X-pipe, you're in excellent shape.


All V8 Cougars have factory cast iron exhaust manifolds. A stock or aftermarket H- or X-pipe will not bolt up to the factory cast iron manifolds without fitting and leaking problems. So when you're planning your dual setup, you must take this into consideration.

Mustang 5.0L Factory Headers

The most popular option to get around this is using the lightweight factory headers from a 1986-1995 Mustang 5.0L motor. Honestly, most Mustang guys would be just as happy to throw them away. Therefore you can probably pick up a set for next to nothing. Using these factory-style headers is also a great guarantee that any aftermarket Mustang exhaust will bolt right up.

Or you can go with aftermarket headers, pocketbook permitting. There are two basic kinds of small-block Ford V8 "shorty" headers: equal length and unequal length.

Mustang 5.0L Unequal Length Headers

If you've got the stock 140-150hp motor, or have converted to HO and are running the stock HO setup, and you will not be doing any other future motor work, it's recommended to use 1-1/2" unequal length headers in conjunction with a 2" or 2-1/4" exhaust system. Unequal length headers are much easier to install than equal lengths while still giving a tuned sound. On these cars, there will be little-to-no modification of the tubes for any clearances around the block.

Mustang 5.0L Equal Length Headers

Any motor over 225hp, or using radically-worked heads, should use 1-5/8" headers. Equal-length headers (the ones that look like a bunch of twisted tubes) can be used for higher-horsepower engines, although getting them to fit is sometimes difficult. There is usually an issue or two around the oil dipstick tube, or even a motor mount, and provisions will have to be made to get them to fit. However, the payoff for equal-length headers is better low-end torque and a wonderful tuned sound. A word of caution: getting equal-lengths to work with a column shifter setup is painfully difficult.

For more radically modified engines there is always the 3/4-length or full length exhaust header. Installation of either will virtually require a T-5 manual transmission; although we do know of a few cases where they were modified to fit around an AOD casing, that is exceptionally rare and costly. These headers are typically used for race cars and are not terribly practical for the street.

One last thing to remember about aftermarket headers: they are designed for an engine, not the compartment where the engine resides. You may have to move, bend, tweak, cut, or modify something around your engine to get headers to fit. That is the nature of hot rodding but please be patient, as the rewards are worth all the effort.


Another annoyance has to do with your gear shifter. Most Cougars came with the column shifter from the factory, and only XR7's and optioned-out cars got the floor shifter. The column shifter uses a whole bunch of rods and linkage right around the driver's side exhaust manifold to connect to the transmission. For this reason, no matter what automatic transmission you've got (AOD, C5), your linkage will present a problem with the exhaust system on the driver's side. Using the stock Mustang headers is a great choice here because they usually clear everything just fine. But you will definitely have to watch with the O2 sensors (see below). For an AOD with the column shifter, you can usually get the O2 sensor to fit between the linkage with no clearance problems. You may end up rearranging some linkage a bit, but it will work. Other transmissions may also have a similar solution. Best thing to do is measure everything and make sure you'll be okay.


Now with the floor shifter, there's another unique problem. The bracket that holds the kickdown cable (aka TV/throttle valve) on the transmission hangs down just enough to interfere with the H-pipe. You will need to grind down the bracket approximately 1/2" to get the H-pipe to fit right. There is nothing more annoying than having the H-pipe squeak every time you hit a bump! For all transmissions alike, please be aware that the factory H-pipe with 4 catalytic converters comes really close to the kickdown linkage on the driver's side of the transmission. If you're not careful with clearances in this area, your kickdown cable can get stuck on the top of the converter and you'll experience some nasty shifting. This is not a safe situation. Our advice: remove the heat shield surrounding that particular converter (the smaller one, toward the front) before you install it. That should assure you of no clearance problems in that area and it won't affect the performance of the converter.

O2 Sensor Extension Harness

When replacing the exhaust manifolds, you are also removing the oxygen sensors (aka EGO, HEGO, O2 sensors). For any computer-controlled engine, especially with Ford's EEC-IV system, you CANNOT run the vehicle without O2 sensors in place, or else your fuel economy and performance will suffer greatly. You can also cause severe engine damage so please, do not even think about letting them hang or disconnecting them. So what to do? Well, MAC makes aftermarket headers for 1994-95 5.0 Mustangs that have O2 sensor provisions. That would be the most practical solution. But most of the time they go in the H- or X-pipe, downstream from the motor a bit. All aftermarket and factory H-pipes have provisions for O2 sensors, essentially a bung with a 15mm thread. You can either lengthen the wires on your existing O2 sensors (if they're newer), or you can get the longer O2 sensor wiring harness from a Mustang that will bring the wires down closer to the H-pipe. That's a nice little salvage yard piece, or it can be bought new from IST. If you need new sensors anyway, Bosch sells new sensors with varying lengths of wiring, so you can probably just use those and keep your stock O2 sensor harness. Now you will have to watch the connectors on the O2 sensors, as there are different types. Best thing to do is take your old ones to the parts store and compare the ends with the new ones. If you are putting your own O2 sensor bungs in a new pipe, you will need to place them on the bottom side, before the crosspipe (the "H").

Mustang H-Pipe

This is what makes true dual exhaust dual, and what most people think of when you picture a Mustang-style dual exhaust. For a used H-pipe, try to find one that has had all 4 of its catalytic convertors replaced under factory recall. As you may guess, it's very expensive to replace all the cats. For a new H-pipe, aim for a 2-1/2" setup with 2 high-flow converters, or an off-road H-pipe if legality won't be an issue.

Mustang X-Pipe

The X-pipe is a relatively new idea for passenger cars. Long used by NASCAR, it equalizes the pulses from the motor better than an H-pipe. This results in a significant horsepower increase (usually between 10-20 or more for just the X-pipe alone), as well as a very strong and very different exhaust note. You can get an X-pipe with high-flow converters or without any converters at all. If you need low-end torque, the X-pipe would probably not be a wise choice. Still, if you want something different, the X-pipe is for you.


When purchasing a cat-back Mustang exhaust system, you're confronted by a few choices, and most of the time it usually revolves around how much you have to spend. For all practical purposes it is not wise to reuse an old Mustang exhaust, no matter how tempting. You're much better off in the long run with a new system. Besides, there's nothing like putting on brand new parts. So at the very least, you should purchase an aluminized system. These are the cheaper of the two kinds of kits, and provided you don't bang up the pipes too bad, they're good for roughly 7-10 years of rust-corrosion resistance. Not a bad investment at all. Some of the more popular brands are Flowmaster, Dynomax/Walker, and Thrush. Each kit will fit very differently, but all do pretty much the same job.

On the other end of the spectrum, there is the stainless steel exhaust kit. The most widely known stainless kit is made by Borla, although there are a few others coming into the picture now. Now these kits are really wicked and install like a dream, but they're frightfully expensive, and usually out of the reach of most people. However, the trade-off is that they will never rust. It's quite literally the last exhaust system you'll ever buy for the car.

Also, you can't forget about tube width. Most places will stock 2-1/4" pipe, and should have 2-1/2" pipe, the two sizes that are the most popular for a Ford 5.0 motor. But width will depend on your power output—bigger is not necessarily better. If you've got a stock 140-150hp 5.0, then you'll want to go with the 2-1/4" pipe. The advantage over 2-1/2" pipe is that it fits much better, so less chance of rattling around. Anywhere from 200hp and up, the 2-1/2" system is best for optimum flow. Ultimately, you must decide for yourself what is the best and most cost-effective for you, and make the best decision you can from there.

Now since our cars have quite a bit more body after the rear axle than a Mustang, the tailpipes may need to be lengthened a bit around the fuel tank. This depends upon if you really want them to look good or not. If you're not really concerned about the looks, then a shorter tailpipe won't hurt you a bit. Mustang LX tailpipes are generally longer than the GT pipes.


We've had several people report that their custom exhaust systems cost less than the cheapest aftermarket kit. That's a significant savings! But in order to find out if this is cost-effective for you, you will have to do a little research in your area. Mainly you'll have to call or visit muffler shops and find out if they can do this for you, and also to get some pricing. Then simply weigh them all against each other. But first you must arm yourself with some understanding and knowledge of what you're about to get into.

Exhaust systems can be made from 3 different types of steel: regular, aluminized, or stainless. All 3 types will carry a different price, and you have to know this going in. Regular steel exhaust systems are very cheap, but they will also need replaced every 2-3 years. Not just the mufflers—the entire thing. This is not usually the most cost-effective way to go, although the price factor could be tempting. Now an aluminized system takes the same gauge steel tubing and adds an aluminized coating to it. This greatly enhances the metal's rust-preventive properties. In fact, the average aluminized system lasts for 7 years! And the plus side is, it's not much more than plain steel. If you are going through the trouble to put a custom exhaust on your Cougar, please do not consider using anything less than aluminized tubing, or else you will simply be throwing your money away. Now this usually does not include aluminized mufflers—they'll still have to be replaced every few years, more than likely, unless specified by the manufacturer. Since exhaust systems rust from the inside out, it's almost impossible to offer a warranty on aluminized mufflers. The third type of exhaust system uses stainless steel. This is the same type of steel used on your silverware, and it's known for its excellent rust-fighting properties. Stainless exhaust systems are the cream of the crop for this fact. And that also means it's the most expensive. Stainless pipe is much thicker, requires special cutting tools, and must be bent while packed with sand or similar substance. You can see now why it costs so much. But the tradeoff is that this will literally be the last exhaust system you'll ever buy for your Cougar (barring accidents, of course). You will pretty much never have to worry about rust eating through the pipes. You will never have to worry about replacing stainless hangers (if they are used). And the finish usually stays shiny and metal-looking for years. This is THE best you can get. So the type of steel used in your custom exhaust system will have a big impact on your wallet.

Before you go taking in your parts that you just bought to the local muffler shop, please check first and make sure that they will install your parts. Some places don't like when you do that to them. If you're allowed to bring in your own parts, and they'll hang them for you, then you may want to look for some mufflers. Not just for performance, but for sound. Let's be honest, the sound factor is half the reason why you're putting duals on in the first place. (The other half is seeing that other pipe hang out the passenger side). So you may as well go for some great sounding mufflers. The major exhaust companies (Borla, Flowmaster, Walker/Dynomax, etc.) do indeed sell their mufflers separately. If you've never heard any of them, talk to a few Mustang guys or hot-rodders. They can give you great input on which ones to get, according to sound. Where do you buy these parts? Best place to look is a high-performance parts catalog, such as those by Summit Racing or Jeg's.

Mustang H-Pipe Hanger

The hooks on top of the H- or X-pipe are for hanging the pipe onto the transmission mount bracket—make sure you do this! You might want to pick up the double-type mount from a Mustang and put that on; however, your stock single-type will work adequately if you can't find a double mount.

There is an air tube on the H-pipe that you can't forget about. It's hooked into the Thermactor air system on the car. The air pump (driven off the car's fan belt) feeds fresh air to the heads and the exhaust. This H-pipe air tube is where the fresh air comes in; its basic function is to allow the catalytic converters to receive oxygen so they can catalyze better. The air tube runs between the H-pipe and the junction under the hood, on the passenger side, right next to the header in the rear of the compartment. If your air tube is broken or missing, it is acceptable to run a good quality high-temp hose between the H-pipe and the junction, provided you clamp the hose down accordingly.

We'd also recommend using the new-style band clamps for the entire exhaust system instead of traditional clamps, if possible. They look awesome, provide a 360 degree seal, and are stainless steel for long life. If your exhaust system is aluminized or stainless, or you're looking for a leak-free and permanent system, then have all the joints and seams welded.


Depending upon where you live, there can be some rather strict laws against modifying your exhaust system. Emissions being what they are today, we would strongly suggest that you contact someone in your state's BMV about your proposed plans to change the exhaust. Some U.S. states, such as California, allow nothing over and above what came with the car for that model year. So please keep this in mind. Any item that says "49-State Legal" or "50-State Legal" is what you're looking for, because that means it passed stringent U.S. government testing.