Installing a Flowmaster American Thunder Cat-Back exhaust For 1987-1996 F150s w/4.9L, 5.0L, or 5.8L engines

By: Justin Dube

First step is to remove the stock system:

1. Raise the vehicle and support with jack stands (if necessary).

2. Spray some WD-40 on all of the rubber mounts holding the exhaust up. This will make it easier to slide the hangers out of the rubber mounts. I like to use WD-40 because it evaporates fairly quickly, and will not lubricate the rubber and let the hanger easily slide out after it dries.

3. Using a hacksaw or sawsall (recommended) cut the stock tailpipe off where it exits the muffler. Make sure that when you cut it, allow the hanger to still hold up the muffler.

4. Remove the tailpipe and toss it aside.

5. Support the muffler with a stand or jack, remove any clamps at the back of the muffler.

6. I recommend cutting the hanger off the muffler pipe first. Then remove the rubber mount from the truck. That way, you can easily slide the remainder of the hanger bar out of the rubber mount in your hand, rather than on the truck. Turn and wiggle until it comes free.

7. Once the back of the muffler is free, it may be necessary to heat the connection to the catalytic converter to ease removal. Please use extreme caution!

If you can’t easily remove the pipe there is a trick. You can cut the stock head-pipe off about 4 inches from the cat. If you do this, you can just slide the new Flowmaster head-pipe from the kit over it, and cut the other end of the Flowmaster head-pipe the 4 inches shorter to compensate. If you have a 139" or 133" wheelbase, you have to cut the Flowmaster head-pipe anyway, so it does not matter. Measure twice cut once! If you have a 155" wheelbase, you don’t originally have to cut the pipe, but if you use my trick you will have to cut it the 4 inches to compensate.


This is the pipe that comes out of the cat. You can see the tab that you are
suppose to line the new pipe up with, but you don’t have to.



This shows where I put the screw in the bottom to hold on the tip.


This picture didn’t come out well but you can see where the tips exit. Those lights are going to be removed and relocated.



This is a side view of the exhaust tips.




Installation of the Flowmaster kit:

1. Place inlet pipe in position on the stock pipe to the catalytic converter. Align the notch in the pipe with the tab on the head pipe and install a 2 �" clamp, but do not tighten at this time. If you used my trick, don’t worry about the notch. If you have trouble sliding the pipe on, take a wire brush and get the loose rust off. Then with a block of wood, hammer it on.

2. Start the engine and rev it up hard, doing this will blow out any lose particles you disrupted in the catalytic converter when you removed the old system. (Enjoy the sound of no muffler for a little while). However, make sure you don’t leave it running long, otherwise you will heat up the pipes too much and you will burn yourself.

3. Slide the head-pipe over the inlet pipe. It will be necessary to cut this pipe to length if you have a 139" or 133" wheelbase (if you used my trick, you’ll have to cut for a 155" wheelbase too). Place a 3" clamp onto the connection, but to not tighten.

4. The muffler is a little heavy, so put the muffler onto a floor jack, lift, and slide the muffler onto the head-pipe. Install a 3" clamp but do not tighten.

5. Slide the two hanger clamps supplied in the kit on to the rubber mounts above the muffler. Then clamp them to the muffler, but do not tighten.

6. Place the right side tailpipe in position over the axle and into the right side muffler outlet. Then place the hanger welded to the pipe, into the rubber mount. Then place the 2 �" clamp onto the muffler’s right outlet. But don’t tighten at this time.

7. Lower and remove the spare tire. This makes it easier to install the left side tailpipe. There is plenty of clearance to put it back. Good time to check its air pressure and condition.

This shows how the pipes bend around the spare tire.






8. Place the left side tailpipe into the left side outlet of the muffler. Support the tailpipe with a stand.

9. The next thing to do is figure out where to put the hanger for this side. There should be a hole in the frame to bolt the supplied hanger to. If not, you will have to drill one. Be careful of the gas tank.







This shows where I put the hanger supplied in the kit.



10. Once you bolt the hanger to the frame, slide the tailpipe’s welded hanger into the rubber mount. It would be a good idea to spray some WD-40 on the rubber mount to make it easier to slide the hanger into it.

11. Now you can slide on the exhaust tips. I recommend drilling a hole in the bottom, and putting a screw in the end. The tips are a little loose when only slid on.





12. Make sure there is proper clearance around the pipes, about 1-2 inches should do. Once you have everything positioned the way you like it, you can tighten everything down.

13. I didn’t like how loose it felt, so I installed a universal hanger to tighten things up a bit, you might want to do the same.

14. Start the truck up, and put your hand around all the connections to check for leaks. For a better look, you can take the truck to a muffler shop and have them weld the connections, but using clamps will be okay.




This kit includes everything you need including clamps, hangers, hanger brackets and 2.5" stainless steel tips. I took some high heat 1200-degree spray paint, and painted mine blue before I installed it. The easiest way to do it is put a rope through the pipes and hang it in the air off a tree. This works better than doing it on the ground. It gets scraped up a bit during installation, but you can touch it up while it’s on the truck. Painting it a color really adds a custom touch. This will also prevent rust on the outside, and lengthen the life of the system. It is aluminized for a long life already.

This kit comes with a 50 series muffler that is not exceptionally loud. You can hear it under acceleration but that is about it. When you are on the highway with the windows up you can barely hear it. I wish they would give you a 40 series, but the 40 series is smaller and doesn’t fit without custom work.