Replacing the Muffler with a Resonator


Turbo Exhaust Theory

I had my old muffler removed and replaced with an Aero AT5050XL 5 inch resonator on my Cummins M11 ISM 450.

I decided this job was better left to someone else who would have the correct pipe and fittings. After deciding the trouble it would be for me to find the exact parts needed to replace the muffler..

I found the Aero AT5050XL on Ebay for $103.00 and took it to Freightliner in Ontario CA

They charged $703 Parts and Labor. Total cost for Replacement $806.00

The parts for my install is
- 10 inches of 5 inch stainless flex
-connected to a 90 degree 5 inch elbow
-connected to a 45 degree 5 inch elbow
-connected to a Aero 5050XL Resonator
-connected to a 5 inch chrome exhaust tip
-several new clamps and a couple of new hangers, which was used to reach the bracket that held the old muffler.


Resonator Replacement

DB before replacement was 93 - 95 db and after there was no change in db but a nicer sounding growl.

Exhaust System Replacement - 2003 U320 Photos by Barry Beam 2003 U320 40'


While I had it on my mind for awhile, I wanted the upgrade to the 500 hp ISM500 @ 1550 ft lb, Problem started when they attempted installing the new bypass turbo, they could not get it hooked up to the down pipe (Discharge) because there was not enough flex in the original configuration, all stopped at that point. I told the Cummins shop men, not to worry, put it back for now, I will modify the exhaust to make it simpler. That is when the resonator appeared, that is how I found how much it improved the stock ISM450, nearly unbelievable, now it was time for the upgrade to the 500. After the new turbo, air pressure control valve in the intake (pressurized) to operate the bypass turbo, then the new fuel settings, things really started going my way. The shop mechanic could not believe how easy the turbo mounted with the long flex and resonator. The NEW setup will never go back to original, No way, I now have better fuel mileage and far better power, feels like what I would expect from 100 hp, guess it is all the torque that hits you in the butt. Dave M. 2001 U320 36'


As you will see in them there is a large area left where the old Muffler sat. I re-used a 90 degree elbow from flex to an adapter I had made, to go from 4 to 5" to accomodate the Resonator which is just before the last chromed outlet thru the Body.

I had 4" piping from Turbo to muffler so that has not changed and on the outlet of was 5" to exit. That is what I have kept it at. 4" from Turbo to adaptor at end of flex then 5" into and out of Resonator to exit. I would also (repeating myself again) strongly suggest that if anyone is contemplating doing a change in this area they do what I did -take off the side panel-as it affords so much more room to move about in and taking off that old massive can of a muffler was made easier(the hanger bolts had rusted etc) and tough to get at with my bad back. It is very easy to take panels off and put back.

I did my own work and it was very easy. it cost approx $75 for the 4ft of stainless flex, resonator was around $80 and clamps $18 each (3) hangers $15, and I used the old tailpiece again as it was good. With my bad back it was 4 hrs from start to finish and too take off side panel and replace add another 1 1/2hrs. Alot easier than I was expecting. your 320 may be different than my 295 Exhaust System Replacement - 2000 U295 Photos John Haygarth 2000 U295 36'


My engine is ISC 8.3 I removed the stock muffler and played with a few different setups. My goal was to see how much the stock system hampered airflow through the engine, if any. The stock system has several turns in the piping. I eliminated almost all , four inch stainless steel flex approx 42" long into a 4" to 5" increaser into a 5"x 36"long chrome turn down. Was a little loud at idle, so I installed some ceramic fiber. Just right sound at idle. The engine now spools up faster BUT the big advantage was the long hills around Cinn. Oh. are now a easy pull AND a lot less heat ,I think the MPG went up 5%. Mind you I am not in any way abusing or hot rodding , just wanted to have the engine breath easier with less heat. Gary & Sharon Karnes 1999 295 36'


I've got an ISC 350 (99 U-270), and had the exhaust manifold crack all the way through. The crack was 1/32+" wide, and leaked plenty, wouldn't let the turbo spool up much, lots of black smoke out the tailpipe. Had it replaced about a year ago at Cummins Gillette, WY. The manifold was s 2-piece design (maybe all 8.3's are 2-piece?), and I had them replace both pieces. No idea if or how long there was a surface crack, but I would get it replaced, since it will seriously cut your power down if it gets as bad as mine. Apparently Cummins 8.3's have a history of exhaust manifold cracks, and the replacement is a revised design.

Finished the muffler replacement. Resonator installed, side back on. Tested it briefly, and it's not really much noisier at idle or with minor revving (haven't had it out on the road yet. I hear somewhat more hiss from enthusiastic exhaust gases leaving, but not at all bad. The test will be going through a tunnel under full power :)) Pictures follow. Didn't show the rear most hangers that locate the tailpipe through the fiberglass, but they're there (mostly reused the old ones that I had added a while ago. The resonator is 10" in dia, and body is about 12-14" long (forgot to measure before I buttoned it up) so slightly larger than the short Walker. I expect to have to re-tighten the clamps and brackets after it has been hot, but everything is so easy to reach from underneath now! Body panel went back on in ~30 minutes. Next time would be less than 15 min (had to find some replacement screws). Definitely the only way to work on the exhaust!! I assume that the other side panels remove as easily, so that will make replacing shocks and air bags dramatically easier.

I actually wanted to have a little give in the mounting, so the supports are only mounted at the top. I'm now reconsidering that and may anchor the bottom of the inboard support angle to the engine cradle plate. The flex pipe should provide plenty of compliance for engine movement, since that's all there was for the old muffler. May also run a more vertical support (flexible hanger) down to the outboard end of the muffler so the muffler won't sag if the joints loosen (but if it does, it will just rest on the angle underneath. Always fun to design. And the pipe does have a low point just outboard of the muffler, but I'm expecting it to get plenty hot, so shouldn't be a problem. The rigid tubing and the muffler are all al-clad steel. Clamps, flex pipe and the final tip are stainless. Decision was driven by what Truck and Trailer had in stock. When I get back East to visit my buddy with a TIG welder, I may redo it all in stainless, which would also be fun. Said it before, but I can't say it enough - working on the exhaust with the side panel off was really wonderful. No rust and grit in your eyes, lying on your back (to say nothing of the fun there would have been getting the old muffler out...) Forgot to answer about the screws - I found flathead stainless screws (same size) in my collection and used them on the flange next to the rear compartment. Used the ones that were there to replace a couple of munged ones that were visible.

It's pretty easy to remove the side panel, and what a difference in workspace! I got resonator, flex pipe, elbows, pipe, reducer, clamps, etc., from Truck and Trailer Parts in Tucson (we are down in Benson now). Don't remember what brand the resonator is - probably Walker equivalent, and short. Tomorrow I will fab the hanger structure. I'll post pictures when done. And we will see how loud it is... I do know that the rig is much lighter on that side with the old muffler out! I'm guessing 80-100 lbs or so for the old muffler, but then the new resonator and plumbing adds some back.

Good idea to wrap the pipe next to the condenser! I've been planning to wrap the exhaust downstream from the turbo anyway, to reduce the heat in the engine compartment.

Sure is a lot easier with the side panel off!


It occurred to me as I was replacing the panel, that full body paint might make removal/replacement of the trim a little harder/messier. Maybe get Extreme to paint the trim separately? (We're planning to have our coach done at the end of the year.) Any thoughts from those who have full body paint? Hate to have to cut the paint at the joint to get things apart. Exhaust System Replacement - 1999 U270 Photos Dave and Nancy 1999 U270 36'


The resonator mod on my 99 320 was so easy I thought I had done something wrong. JC 1999 U320


I had my 50 gallon drum / muffler removed and replaced it with a Magnaflow I can't tell you of any MPG increase, as I've just started tracking my mileage, but I can tell you that my spool-up time has been cut by at least half! No discernible difference in the exhaust noise. Brian, 1999 U270 36'


There is a guy who stays the winter at la pas campground in parker az. who is a dealer for aero. I bought my aero 5050 from him last year for $130.00. I had been running a straight pipe for a few thousand miles, but it was just too loud. the new exhaust is a great upgrade.

This project started because the original flex pipe looked to me like it was going to fail. getting rid of a muffler is just something that comes natural to me. I stripped everything off from the turbo downpipe back. you can see in the pics that I kept the old rubber mounted bracket that the muffler was hung on. I have hung 2 new hangers from this bracket. besides the new flex pipe, an adapter, 3 elbows and a new 5 inch exhaust tip there was not much to it. I still have to remove the exhaust tip and increase the size of the hole where the tip comes through the body. if the noise turns out to be too much, an aero muffler will fit in the straight run of pipe. from what I have seen, the same project on an M-11 would be a different kettle of fish. I have also been looking into a double turbo install, that would let me run with the big boys, but that is for another day.

the required parts for my install is 
   - 36 inches of 4 inch stainless flex
   -connected to a 90 degree  4 inch elbow
   -connected to a 4 inch to 5 inch adapter
   -connected to a 24 inch piece of straight exhaust pipe
   -connected to a 6 inch female to female adapter
   -connected to a 60 degree elbow
   -connected to a 45 degree elbow
   -connected to a 5 inch chrome exhaust tip
-several new clamps and a couple of new hangers, which I had tomake extensions for, to reach the bracket that held the old muffler.
-also the hole where the tip passes through the body had to beenlarged enough to accommodate the 5 inch tip, with sufficient clearance around the tip.
total cost of the parts including the chrome tip was around $400.00 ca.

Exhaust System Replacement - 1998 U295 Photos wayne macauley 98 40' 295


I didn't have much luck with FOT or MOT when I was rounding up parts to replace my exhaust system. Take a look at photo #13 of the following to see my bill of materials; I've been extremely pleased with what my son and I put together. I like it a whole lot better than the original design; lighter weight, much less mass radiating high heat, AERO design prevents the impounding of exhaust products, smaller (muffler/resonator) cross section, all 304SS components, system stability (doesn't beat up the fiberglass exit port), mellow SOUND, gains in performance and maybe even fuel economy (slight, but the engine definately breathes better). A good truck shop, that's willing to work on your coach, should be able to do the same thing. FWIW, Neal Pillsbury 1998 U270


Exhaust System Replacement - 1998 U270 Photos

Neal Pillsbury 1998 U270 36'


On my setup, I used 1 90, 1 45, about 4' flex, and for the straight pipe, used the existing pipe between old muffler and tail pipe, keeping and using the chrome tip that stick out through the body, about 5 band clamps and two HD hangers. Worked out well for my setup., I cut the elbow off the down pipe so a 90 would aim in the correct direction, then the flex, then the 45, then the resonator, then the tail pipe. Real simple. Special tool used, PortaBand, 1/2" air wrench, rest were normal toolbox items. If your not familiar with the band clamps, make sure when you tighten them up, until the saddle is bottomed out 100% so the band stretches and forms around the parts you are securing. The air wrench makes this very simple if it has the torque to get r done.

Here is the Walker manual for lots of items of interest including the resonator, clamps, elbows etc etc and more etc.l Anyway the Resonator part number is 21835 It should be available at any truck supplier that handles Walker exhaust parts.


These were not avail for awhile, seems to be back in stock. This is what I would install if I the my muffler needed replacement. Aero-Turbine Resonated Performance Muffler 5050L Then for the exhaust wrap... Thermo Tec Exhaust Insulating Graphite Black Wrap #11023 . Clamps work ok with the flex? I'm looking at 5 of the Stainless lap joint band clamps... Walker Exhaust 33276 - Walker Lap-Joint Band Clamps - Overview -

I plan on contacting my favorite exhaust guy in the next two weeks to let him decide on whether the Aero 5050XL is worth the money or to just go with the Walker. I really feel 'overhyped' with respect to the Aero...Dave Head 95 U320C SE 40


Dave, First on the first one you mention, it sure looks puuurty, but a 5"hole thru is a 5" hole no matter how much chrome you put on it ? The shown Walker resonator loooks very short, they are not long, but that one is real sort looking. The purpose of the resonator is to reduce the high pitch sounds while allowing unrestricted exhaust flow (they are directional) or at least that is what happens to the units I have installed them on. My OPINION is the short versioln resonator would not reduce the high pitch sound as much. I am sure there are book educated folks on the forum that can clear that up, Just MY OPINION from sperience. I vote for the standard alumaized resonator. Not a shorty as there is plenty room to install.

IF I was faced with the need to replace a muffler on my coach, I would simply discard the present muffler, run a straight pipe with a resonator in line to remove the harshness. From a legal point, the turbo is a muffler by some standards. A lot of trucks run that way with out any issues from anyone. Did that on my MCI conversion and loved it, The resonator is about 12" L X 7" D with a five inch hole thru it, using the band clamps, it is a easy job. Unknown by me, but it sure did wonders for my 8V-92TA (580HP) in the MCI. At first I ran with no resonator, was a little harsh, so installed the resonator we had laying around the shop, BINGO, cut the harshness and did not affect the power one bit, So I loved it. Dave M. 2001 U320 36'


Dave I had my muffler replaced with the AERO 5050xl at the Family Reunion in Madison WI. Drove home to Niagara Falls On (flat land) and really enjoy the Big increase in hp. MPG looked like 20% increase. niagarachip 1997 U320 40'


Our original exhaust was all 4" and we now have a short original piece of 4" attached to turbo and 5" from there to the back fiberglass exit hole. Since the fiberglass opening is still 4.5", we decided to temporarily use our 4" chrome tip attached to a 4" to 5" transition. Sometime later, we will remove the 4" tip, widen the fiberglass to 5.5" and bring 5" pipes out the rear.

Aero has two mufflers to choose from in the 5" range: AT5050 which is 20" long x 7.5" diameter. AT5050XL which is 30" long x 6" diameter. The 20" AT5050 fits better than the 30" XL in our coach. Exhaust System Replacement - 1997 U270 Photos by Barry and Cindy 1997 U270 36'


My install was as easy as everyone else has said. I used all Walker parts, total cost around $250. I re-used the flex pipe and bottom 45 bend. Then new 4 to 5 adapter, 5" 45 bend direct into the resonator. Then a 5 foot piece of pipe that had a tip on it, actually was intended to be a vertical stack on a truck, to go out the back. It's hard to tell in the pictures, but it all runs at an angle from where it hooks onto the flex pipe to the exit. A few new clamps and done. Exhaust System Replacement - 1996 U270 Photos by Gayland Baasch 1996 u270


Here is a picture of my muffler replacement that was done last year. I stayed with 4" pipe and the muffler is an Aeroturbine 4040XL. I used the 2 old rubber mounts from the original muffler that were still in good shape. Fabricated new brackets and bolted them to the frame. As you can see the shiny SS muffler discolors in use. Foretravel chrome exhaust tip is not shown. I have not noticed any improvement in mpg or performance, but hopefully there is some. The idle noise is a little louder, but going down the road I don't hear any difference even with the drivers window open.

Resonator install

Jerry Whiteaker 1996 U270 36'


Check out this link? Is this the right part? looks like $127 with free shipping? Aero Turbine 5050 5in in/out Muffler [AT5050] - $127.00 : Moe's Performance, Tim Fiedler 2000 U-320 40


That is the 'shorty' model. The 5050XL is 193.50

I'm looking at FTE Resonators. They are popular with the Cummins truck crowd...

Resonator / Muffler 5" Stainless Steel, perfect for performance exhaust systems with un-wanted cab noise or drone.

This unique spiral design virtually eliminates the unwanted sound while keeping flow characteristics for both performance and EGT reduction.

Small and Simple Design makes this unit ideal for mounting in tight areas, heavy construction ensures it lasts a long time. See what customers are saying about their experience with this amazing product at, this product has proven itself to work great on all diesel powered trucks alike (Cummins, Powerstroke, and Duramax).

5" ID Inlet & Outlet
5" maximum diameter x 17.5" Over All Length - 12" Usable T409 SS Body
Eliminates irritating "Drone" & Cab Noise, maintains good sound out tailpipe or stacks
No gain in EGT or reduction in flow Premium grade product
Exhaust Parts Size: 5.0"
Material Type: SS T409
Finish: Matte
List Price: $145.95
Price: $106.75

Dave Head 95 U320C SE 40

Here have been several discussions on about the Aero mufflers. Most find the noise level high. Consensus is that MagnaFlow is quieter and gives virtually the same performance:

There is a VAST difference in exhaust CFM between a Cummins B engine and an L or M engine. I know the muffler on our Caterpillar 3116 (U240) is well oversized for the CFM requirements of our engine-- so little back pressure. But, if this same muffler were used on a large engine, it may be undersized. Said another way, I doubt there is an across the board answer as to performance or MPG improvement, as back pressure is not the same on all applications. Brett Wolfe 1993 U240


Well, it was my turn to put in a new Exhaust system. I had Cummins in CLoverdale do it over the last couple days. I had a hole in the muffler and it would not pass VA state inspection so I needed to replace it. I used the same resonator that Dave M used but my set up is a bit different with the batteries right by the down pipe off the turbo. It took a full day to find the parts and piece it together. Then we had to weld on new hangers and gussets too. The tech took the completed piping home and tig welded it for a great tight fit and very few bands ( only two were used).

I think the best thing I can say is it sounds a bit different but the performance is much much better. I have had Silverleaf for a long time now and I have usually seen my turbo pressure on full throttle pushing hard no higher than 27 to 28 but after the change out I hit 30. I also merged onto I 81 on an uphill run where I never got above 45 prior at 57 and one big hill that slowed me to 55 was taken at 72 all the way. THe other thing is I have always fun about 7.5 mpg on the way home up I 81. It has been that as long as I did not hit traffic running the speed limit. Today I ran 72 and finished up at 8.2 MPG. That mileage difference will have to be checked over more miles but it was about 200 miles and a regular route I run all the time so I have records of the mileage for it over many trips.

I will have to see when I fill up next how close I am but the Silver leaf is usually within a couple gallons on a 50 plus gallon fillup as long as I did not use the genny and I did not as it was only 60 degrees out. So, I am very happy with the improvements and I hope that I can run a few more miles soon and see the differences. John S. 2001 42' U320

This post is an attempt to summarize the information from "John's Resonator Upgrade" thread supplemented with internet research:

Dave M replaced original muffler with Walker 21835 plated resonator

Dave Head plans to replace original muffler with either:
     Aero 5050XL ($200 - SS muffler/resonator combo) or Walker 21835 ($65 plated resonator)

Dave M recommends "standard length resonator" (not short).

niagarachip replaced original muffler on his 1997 U320 with Aero 5050XL muffler/resonator.

Wayne M replaced original muffler on his 98 U295 with a pipe but it was too loud.
Wayne M replaced some pipe with Aero AT5050 ($130 SS muffler).
Wayne M indicated that the Aero 5050XL is quieter than the Aero AT5050.

Brett Wolfe indicated that Magnaflow seems quieter than Aero (see

I did a little research on mufflers/resonators mentioned in this thread.
Here is a list of various products I found - there are more.

Aero AT5050  $130 304 polished SS muffler, 5 in, 5 out, 20 long, 7.5 OD body.
Aero  5050XL $200 304 polished SS resonated muffler, 5 in, 5 out, 30 long, 7.5 OD body.

Diamond Eye 460100 $85 plated LOUVERED muffler  5 in, 5 out, 30 long, 8 OD body.
Diamond Eye 460041 $110 SS PERFORATED muffler  5 in, 5 out, 30 long, 8 OD body.

FTE RM5517ss $107 T409 SS resonator, 5 in, 5 out, 17.5 long, 9 OD body
FTE RM5530SS $135 T409 SS resonated muffler, 5 in, 5 out, 30 long, ?? OD body
FTE Hushpower $180 15020100 T409 SS/plated muffler, 5 in, 5 out, 25.5 long, 9 OD body

MagnaFlow 12774 $160  SS muffler, 5 in, 5 out, 30 long, 7 OD body
MagnaFlow 14774 $200  polished SS muffler, 5 in, 5 out, 30 long, 7 OD body

MBRP M2050 $135  plated muffler, 5 in, 5 out, 31 long, ?? OD body

Walker 21835 $65 plated resonator  5 in, 5 out, 20 long, 7.5 OD body.
Walker 22914 $?? plated standard muffler  5 in, 5 out, 40 long, 9 OD body.
Walker 22964 $?? plated megaflow muffler  5 in, 5 out, 51 long, 9 OD body.
Walker 22963 $?? plated megaflow muffler  5 in, 5 out, 51 long, 10 OD body.
Walker 22980 $?? plated noise braker muffler  5 in, 5 out, 51 long, 10 OD body.

Most prices listed were from internet discount sites, which were much lower than manufacturer's prices.
The FTE Hushpower is adverised as being "quiet".
The Cummins related websites seem to favour FTE or Magnaflow mufflers.
I found the Walker site difficult to navigate.
I did not find Walker prices on internet discount sites.

In my muffler research, I found references indicating that a larger exhaust ie 5" replacing a 4" can result in more noise (ie annoying diesel engine drone), and different but not better performance. It is engine/exhaust dependent. I would recommend that you seach for muffler or exhaust and your 5.9 engine to see what others have done and the result. Wyatt 96 U320 40


Re Wyatt's list. I did not see the one I used---Fleetguard 86145m resonator a Cummins recommended one (it came out of their books I believe). I did not want a long Muffler as I had no room or wants for it. The Turbo does a good job of muffling the exhaust noise to begin with and the one I got is 11 1/2 long body and about 9" dia. It fitted in well and I am very happy with it. The sound is pu-u-u-r-r-rfect. John Haygarth 2000 U295 36'

I must admit I was skeptical, wasn't wanting to change the exhaust just for a different sound.  However....the folks who have gone before and claimed a performance improvement were, if anything, far too modest.  The turbo spools up much faster, acceleration from a dead stop is 100% improved.  The coach just generally seems happier at cruise and upgrade downshifting is reduced.  As far as fuel mileage can't say, it's still above 10 so I'm happy. 

Here's how I knew right off performance was improved.  Leaving my house there's about 1/2 mile of straight country road I always drive slowly watching out for dogs and critters, checking out the longhorn herd.  This road T's into a very busy 2 lane road and the center of a nasty blind curve with Houston road warriors driving like wild bats to get home.  As is my custom, I nailed the throttle for a left hand turn.  The new acceleration profile caught me by surprise, I almost drove into the ditch on the far side of the road.  This alone is worth the cost of admission.  Sounds boss too. 

The installation scheme reuses the 4" stainless flex, cut down a bit.  I left it as long as possible, in fact it laps over the turbo down tube several extra inches. Next comes the 4X5 adapter, followed by a 5" short ell, then a 5" long ell, then the Aero resonator (I used the longer one) then a 45 deg bend, finally the exhaust pipe. Joining the 4X5 adapter to the 4" flex tube necessitated cutting a sleeve from the old 4" exhaust, this is slipped inside the flex exhaust and the adapter and the single flat band clamp goes over that joint.  It might be possible to avoid this with a different adapter but I bought what was available. No exhaust parts are contacting anything but the exhaust hangers and the exhaust pipe is staying centered in the enlarged opening.   

Not listed in the parts from Ryder Fleet Products are the resonator Aero 5050XL from "our deals" and the exhaust pipe and one overlooked 4" lap band clamp (I reused the old one but not optimal). Used some 5" aluminized pipe I had on hand as no short lengths of stainless pipe were available. It takes about 24" of this pipe.  Also cut from stock on hand was the 2" X 2" steel angle, approx 48" long that I replaced the original hanger bar with. This was extended from original to allow more hangars along the run of the exhaust.  As installed it runs slightly downhill after the turns to get our of engine area to exhaust,  and parallel with engine and coach.  So, the cost was in the 350.00 range all up. 

If I was doing it again I would remove the side panel, lots of trips back and forth under the coach as I was working out the installation. Hopefully this will help make the job easier for you. Thanks again to everyone who went ahead with this upgrade, it's well worth the effort. 

S48 1
11S50045A 5" Exhaust Pipe 45 degree elbow   $22.48
S48 1
12500A Elbow 90 deg aluminum 5" id 5" od   $29.50
S48 1
12510A Elbow 90 deg 5" idx5 od   $22.87
S48 3
19A500Z Clamp 5" muffler zinc weld   $12.30
S48 1
20400ES Flat Band Clamp 4" Stainless Steel Easy Seal   $6.49
S48 6
20A500 Preformed Lap Joint Band Clamp 5" Aluminum   $39.66
S48 1
28540A Reducer ID 5   $14.79
V831 Universal Tail Pipe Hanger Heavy Duty   $8.16
Total:       $168.20

Resonator 8.3

Resonator 8.3

Resonator 8.3

Chuck Pearson 1996 U295 36'

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