KOOL MUFFLER

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Actually not a kool sounding muffler but wait till you hear the gas mileage increase!  I measured the diameter of the pipe from the back of the CAT converter and end of the muffler for my I6 engine.  It's 2 1/4" out the CAT and 2" out the muffler.  It also has the center input and offset output.  I ordered the 2 1/4" at both ends Dynomax Stainless Steel Super Turbo muffler from JC Whitney

 1994 Jeep muffler replacement  It's a super deal at $99. and if you get their magazine you should be able to get 10% off with a coupon.   Remember you'll pay shipping so if you want to check around other stores.  When it arrived I checked it out.  The advertisement on the box said "straight through design".  They weren't kidding as the front tube is attached to the back tube with a S/S slightly curved tube.  I looked a the loudness advertisement on the box and it was much quieter then others listed.  I figured this was going to be real noisy and would have to add a tail pipe glass pack addition .  I purchased this muffler against another as it was almost as big as the giant muffler on the ZJ.
  I figured taking off a S/S muffler can't be that hard, no rust.  I did need to heat, with a torch, the front muffler clamp to get it off.  That was saved as it was a Sunday afternoon I didn't have spare clamps and stores were closed.  I cut the pipe behind the muffler off with my Sears reciprocating saw & metal cutting blade.  I cut about 2" from the back of the muffler leaving some 3" remaining on the tailpipe.
 
    The rear 2"OD pipe behind the muffler was straight so I figured I should be able to get an adapter on there.  I did not use the large pipe that fit both ends.  The inside of the 2"ID would not fit over the S/S tail pipe, it was getting dark, tried the following.  Taking off the muffler, as you saw from the picture, was not easy.  I could wiggle the muffler but it wouldn't slide back.  I resorted to a 5 lb. sledge hammer. 

 Even with that I still had to cut the front part of the muffler away from the CAT with my air gun. 

1994 Jeep muffler replacement
  Finally it came sliding off, there is about 4" of pipe at the end of the CAT.  When you place the center part of the muffler on the CAT it will not slide in all the way as the inside parts of the muffler prevents it.  You could cut off some of the end of the CAT but I didn't.
   I also added a S/S muffler strap from JC Whitney ($7) to connect 2 - 2" OD (0utside diameter) pipes together.  I just in case I sell the car, I'll put back the old muffler.  This muffler strap would allow that.  I found a 2 1/4 muffler adapter with the other end a 2" OD.  I happen to have a 2 1/4 OD pipe so I cut this pipe to fit inside the muffler and the adapter pipe.  1994 Jeep muffler replacement

  
 1994 Jeep muffler replacement  Two spare muffler clamps held them in place.  I used this S/S strap to reattach the tail pipe and adapter.  These adapters are steel parts, not S/S, so some 4 years from now they may rust out. The S/S strap worked fine (no leaks) but they would not support the weight of this large muffler.  The strap flexed a bit as the welded S/S tail assembly only has one hanger at  the rear.  No other support for the muffler/CAT existed.  I added a $1 muffler hanger from PEP BOYS, an exposed bolt right under the muffler would support the strap.  I bent the hanger strap, below the second hole, at the top. 
 

1994 Jeep muffler replacement
    I fit the hanger clamp between the two muffler clamps.

Now the muffler was not flexing the S/S strap.  The tailpipe is up a bit in the rear but I haven't heard it hitting.

 I started the car expecting a loud rumble, worse than my '86 Fiero, but that car sounded pretty cool.  Nothing.... nope... the I6 engine sounded as it has the standard muffler on it.  My van sounded louder that this straight through muffler.
 

Driving with just myself in the car I noticed these differences:
* Gas mileage from my computer showed mileage was better.
* Highways.. cruse set for 60 mph , straight driving, no hills or declines it would display 25 mpg.
* On steep hill declines, with cruse, the mileage jumped to 59 mpg.. It never went above 45 mpg
    before.
* When in cruse and you tapped the brake to slow, you would feel the car jerk to slow.  Now
    you wouldn't' feel the car jerk to decelerate.  Now it would just slow down.
* Driving in town where the computer use to read 14 mpg was now showing 17 at 40 mph.
* Up my steep hills the gauge use to show 14 mpg, now it's 16/17 mpg.

     My gas gauge also showed improvement.  My usual 35 mile trip to work use to take a bit less then 1/8 of a tank.  Now it used less then that and the weather was colder.  I drive the same stretch 5 days a week, no bumper to bumper traffic.  I can only state what the gas gauge does and computer shows.  I have owned 4 Chrysler cars with these computers and they are deadly accurate.  They show instant (adjusts every two seconds) and current average since a reset.  A gas station is a mile from the entrance ramp to the highway home.  I can get gas, reset the computer, make it through the one traffic light and cruse on the highway and have it show a 21 mpg average 30 miles later just before I turn off.  My normal 4 day trip would show an average of 19.4 mpg (mostly highway).  I even get cheap-o gas.  This station (Denco) is 6 to 10 cents cheaper then brand names.  On 1-16-'98 I'm paying $.99 a gallon.  Last summer they were are $.96 for a number of weeks.