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EVO 8/9 Cat-back Exhaust Install

The stock Evo 8 stock exhaust piping isn't too shabby at around 2.25" ID, but the muffler just sucks. Not only is it baffled like crazy, the exhaust piping enters on the side of the can and the muffler contains a valve which opens and closes. To get maximum reduction in exhaust back-pressure, we will be installing an RMR stainless steel cat-back system with a straight through muffler and 3" piping.

1. Naturally, start off by raising the car and supporting it on jack stands. If you don't have a lift, it may be easier to raise and support the entire passenger side of the car, instead of the rear.
2. Under the rear of the car, begin by removing the three 14mm bolts holding the muffler to the midpipe.
3. On the top/passenger side of the muffler can is a hanger. Rather than try to pull it off, it is much easier to remove the 12mm bolt holding the muffler to the hanger.
4. Once the bolt is removed from the hanger in Step 3, there is one hanger on the top of the muffler can that must be slid out. To make this easier, use some WD-40, 3-in-1 oil or similar, around the rod in the hanger. Hold the muffler up and push the rubber hanger off of the rod. This is the last thing holding the muffler up, so when it slides off, you need a handle on the muffler so it doesn't fall.
5. Time to get that 22mm open end or O2 sensor socket out! Open the folded over tabs holding the O2 sensor wire in place and simply loosen the sensor as you would any other bolt. If you are seriously concerned about the O2 sensor wires twisting up on each other, you should disconnect the O2 sensor harness which is inside the car under the carpeting. TECH TIP: If you don't disconnect the O2 wire harness under the passenger seat and just let it twist as you remove the sensor, count the number of turns it takes for the O2 sensor to come out of the pipe.
6. With the O2 sensor successfully removed from the exhaust pipe, it's time to take out the stock mid-pipe. So as not to put any undo pressure on the downpipe, we will next remove the two 19mm bolts connecting the mid-pipe to the converter. Remove the bolts, but leave the pipe hanging on the studs. Removing the bolts will give some leeway to lower the rear of the mid-pipe without forcing the studs to try to hold up the entire length.
7. Returning to the rear of the car, remove the two 12mm bolts from the last hanger holding the mid-pipe to the rear sub-frame. Again, removing the bolts is easier than trying to the pull the hanger off now. With that done, slide the mid-pipe backwards right off of the converter studs and the old cat-back will be completely out.
8. After you have had your fun comparing why the RMR exhaust is so much better than the stock one and why you spend your hard-earned $$ on it, put the stock cat gasket on if you took it off and then slide the mid-pipe on to the cat's studs.
9. If you haven't already, remove and transfer the stock hangers from the stock exhaust to the muffler section of the RMR exhaust. Unlike the stock exhaust, all 3 hangers attach to the muffler section and pipe.
10. Back under the rear of the car, hang the muffler section by first sliding the top/front hanger on (again, a little lube on the hanger rod will make this easier) and then bolting the top/rear hanger to the muffler with the factory 12mm bolt.
11. After that's done, bolt the last hanger to the rear sub frame with the two 12mm bolts.
12. Now that the muffler section is installed, grab the hardware included and use two 14mm bolts, two 14mm nuts, two lock washers and the gasket to bolt the muffler section to the mid-pipe, which should still be just hanging on the cat studs at the front ;)
13. With the muffler section connected to the new mid-pipe, move back up to the cat, using the two 17mm bolts and last two lock washers, bolt the mid-pipe to the converter. Absolute proof that a 3" cat-back will bolt up to the stock converter!
14. Now, if you have anti-seize paste available, it wouldn't hurt to apply some to the threads of the O2 sensor prior to reinstalling it in case you need to remove it after your Evo has some miles on it. TECH TIP: Remember all the way back in Step 5 when you counted how many turns it took for the O2 sensor to come out? If you didn't disconnect the O2 sensor harness to remove the O2 sensor, now it's time to spin the sensor counter-clockwise the number of turns it took to remove it. Once you do that, thread the sensor into the new mid-pipe. If all goes well, your O2 sensor harness will not have any twists in it when it is fully seated.
15. Start the car. The first thing you'll hear is your new powerful sounding exhaust, but take a second to check for any exhaust leaks and if there are any, correct them before the exhaust gets too hot. Small leaks may be sealed when the piping heats up and expands, so check for leaks first and enjoy the exhaust sound later :) When you are sure there are no leaks, take the car off of the jack stands go for a ride...you will definitely notice a difference!

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