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MODIFYING

DUAL EXHAUST - 3.8L V6

For All 1983-88 3.8L V6 Cougars / Thunderbirds
Revised August 25, 2016

Anything you can do to help free up power in your 3.8L V6 is a plus. Aside from a K&N filter and hotter spark plugs, you're probably thinking of going with a dual exhaust setup. That's a good move since less restriction will free up much-needed horsepower to the rear wheels. There are several ways you can go, but in all cases you will be gaining real-world, usable power.

Fuel Filter

You have to consider a few things first. Owners of 1983-86 Cougars are faced with the fact that the car is not set up for dual exhaust. The main stumbling block is the fuel pump/filter, right exactly where the passenger side muffler needs to go. This is a major situation. If you can have a repair shop relocate them for you, that's a great start. Otherwise, you may be forced to use the only mufflers that can fit alongside the factory filter/pump location: Cherry Bombs. Still, they will fit without modification. Owners of 1987-88 V6 Cougars should not have to worry about that, since Ford put the filter outside the framerail.

Headers

You're also cursed just the same as 5.0 owners with the stock cast-iron exhaust manifolds. They are what really keep the power output down. Replacing them with headers is the best thing you can do to gain power and free up airflow restriction.


1994-98 Mustang Factory Headers - 3.8L V6

Left: You can use factory 1994-98 Mustang headers as they are stout pieces; the same basic headers are also found on 1989-97 V6 Cougars and Thunderbirds. They will also help provide a more aggressive tone to the exhaust system.

MAC Shorty Headers - 3.8L V6

Left: MAC makes V6 1-5/8" shorty headers for the 1994-1997 Mustang (part number TF3845) for around $230 US. Note the air tube sticking out from each one. You do not need this for a 1983-88 3.8 V6 on your Cougar, and will need to plug up the holes or have them welded shut. These shown are for the 1999-up Mustang; buying a 1994-97 part may eliminate those holes.

MAC Long Tube Headers - 3.8L V6

Left: MAC also makes 1-5/8" long tube headers for the 5-speed 1994-1997 Mustang, part number TF3895, for around $250 US. Note that these headers will not clear an AOD transmission casing. Thanks to Chad for the info.

 

Jay reports that if you have a column shifter, the linkage gets in the way and must be moved. The exhaust pipes that bolted to the factory manifold need to be opened a 1/2 inch, rebent and shortened slightly. You'll also need to make a new EGR tube and find a fitting for the header's EGR nipple. You will have the same oxygen (O2) sensor relocation problem as 5.0 owners. There are ways to solve this problem—read on.


Configurations

The first thing you need to do is determine how far you want to go with duals. Do you want just a little more power, or do you want the most you can get? Your budget will probably have a large influence on that. If you can't swing much cash then you will probably be best to stick with your stock exhaust manifolds and Y-pipe. You can have a secondary Y-pipe custom bent from there to go into your mufflers. This is a nice, clean installation and is very efficient since you'll just reuse part of your factory system. If you're going all out though, you're going to want an H-pipe. The easiest way for you to get an H-pipe for your V6 is to get one from any 1987-95 Mustang 5.0. Yes, it fits, although you may have to get it slightly re-bent to fit up to the headers/exhaust manifolds (whichever you decide to run). The H-pipe will have the bungs installed for the O2 sensor(s). If you just have one sensor then you need simply to plug up the other hole in the H-pipe with a 15mm bolt and some Teflon tape. You may also need to lengthen the wires for your O2 sensor. Once that's settled, you can run your cat-back exhaust.


Pipe Diameter

It is recommended that you use a 2.25" exhaust system for the V6. Anything larger than that is overkill and may even cause a slight hesitation. Obviously the driver's side will fit nicely; the passenger side will need to have universal hanger installed for the muffler and tailpipe. Now there are two ways to get a cat-back exhaust: either custom bent or aftermarket. Custom bent duals insure that the fit is excellent. You will get exactly the length of pipes that you need, meaning less chance of an exhaust leak. This is a big plus. The downside is that it may cost you more; however, the quality alone is usually worth it. If you decide to buy a cat-back system you'll need to order it for a Mustang 5.0. The LX pipes will be longer and are recommended for a better fit around the gas tank. You may still need to have new intermediate pipes made (between the H-pipe and mufflers) due to the longer wheelbase on your Cougar versus the Mustang. Since each kit fits differently, you'll have to experiment and see. Some of the popular brands of cat-back kits for Mustangs include Flowmaster, Dynomax and Borla. Each has its own sound and quality of finish, so you may need to do some homework in that area. In any case, you're going to get a really nice system for your car that will free up much-needed power.

You can see that this is not a job for the beginner. In most cases you will probably need to have a muffler shop do at least some of the work for you. The biggest concern that shops usually bring up is that from their point of view, a tailpipe won't fit on the passenger side around the gas tank. No matter what they tell you, it WILL fit—there is plenty of room for it. Besides, Ford was able to get a pipe on that side with the 1988 5.0 exhaust without any fuel tank changes, so that should help persuade some shops. Also, don't be afraid to shop around for price quotes. Be sure to ask about the type of pipe to be used. If you are going through the trouble of having a custom-bent system, do not settle for less than aluminized pipe, which lasts 5-7 years or more. When all is said and done, you will have a very nice sounding exhaust system and much more off-the-line power.

 

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