Moroso Spiral Flow Muffler installation (as a resonator)

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Aug 4, 2004
Spokane WA, USA
Moroso Spiral Flow Muffler installation (as a resonator) on an EMSPowered Header Back LX450 exhaust system

The muffler is a stainless Spiral Flow part number 94054, 2.5 inch inlet and outlet, 4 inches OD, 16 inches long overall. I got mine from Summit Racing and it was delivered to my door in two days. The total cost was US$115. Thank you superjuice for writing up this excellent article, using it as a resonator to tame the exhaust note of a straight-through EMS Powered exhaust system, …

BTW: These are all large hi res pictures – you can open in a new tab to see them full sized.

Here’s the Moroso brochure: ….

A little background: I ordered a “no resonator” system and installed it on my 1996 LX450, which is lifted about three inches. The installation is described here….

As soon as I fired up the truck I knew that it was too durn loud! I talked to baktasht in Texas, and he ended up sending me their resonator equipped tailpipe to try. I really liked the snappy feel and extra power of the straight through exhaust system, and I was hoping that the EMS Powered resonator would quiet it down without dulling the new performance too much.

I received the resonator tailpipe after three weeks, and installed it right away. It is SO easy to remove this rear section – just loosen the slip joint clamp and remove the rear hanger bolt. It is literally a five minute job to swap pipes. The new resonator is a custom unit that EMS Powered builds and installs INSIDE the tail pipe near the tip. There is no external sign of it other than a few spot welds.


Here is the new pipe sitting next to the straight-through version:


I thought that the resonator would consist of some small vanes around the perimeter that didn’t restrict the flow too much. I got a mirror and flashlight and took a look….. UH OH! The device consists of a small diameter center tube supported by discs at each end, which have eight very small holes around the perimeter. I don’t know how many disks there are – at least two. It is a very restrictive design, and it also appears to be made of plain (and rusting) steel. Does anyone with gray hair remember the old motorcycle “Snuff or Not”?



That is essentially what we have here, except that there is no way to bypass the restriction:


I test drove the truck and it was indeed quiet, but the snappy throttle response and extra power were GONE. The engine felt very restricted and choked down and the truck felt as slow as it was stock. My mileage also apparently dropped about a half mpg as per my UltraGauge, though I did not drive more than 30 miles with the resonator installed.

So I immediately ordered the Moroso muffler. I installed it onto my original straight-through tail pipe, and I’ll return the EMS Powered restricted unit if baktasht wants it. I do think it would be interesting to do back-to-back dyno runs with both pipes, but I don’t plan on doing that. If someone here in the Spokane area wants to borrow both pipes for testing, he would be welcome to them.

Here is a shot of the Spiral Flow interior:


The center core is fairly large and straight through. The spiral vanes divert flow into the larger OD of the can, and break up the sound without significant back pressure. Moroso claims 5 to 7 dB sound reduction and 850 cfm airflow. With the can in your hand, it is apparent that it is well built. It’s also very pretty.

Here is where it goes - there is barely enough room for it (lengthwise), so it takes a good bit of fussing and some care to get it installed correctly. One important consideration is to maintain clearance with the cross arm during axle articulation. My truck is lifted, so it has extra room. I don’t carry a spare tire under the truck, so I don’t know anything about fitment with a tire there, or an aux fuel tank.


More to follow.

John Davies
Spokane WA USA
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Start out by wrapping the exhaust tip to protect it from scratching! I used a rag with a 1 gallon zip-lock bag tie wrapped on top - I wanted some padding in case I dropped it onto the floor.

Cut out a section of pipe roughly the length of the body section – 12 inches. You will have to do some fit and trim, fit and trim, so you need to be prepared to use up a few hacksaw blades. If this were going into a long section of tubing that goes straight back, it would be dead simple. But I wanted to retain the original rear support bracket – if you lengthen the angled section where the resonator goes, it will move that rear mount both outward and rearward. Here’s how to get the resonator in and still use that rear mount.

First two cuts:


Here is the resonator clamped in a six inch bench vise with an old piece of mud flap for a cushion and to keep it from slipping. Wrap a piece of narrow masking tape around the extension piece as a saw guide – the entire piece will have to come off right next to the angled part.


It would be possible to use an exhaust tubing stretcher, if you have access to one. Lisle makes a very nice set with a heavy thrust bearing that you might be able to rent from an auto parts store, or you could find a muffler shop that will do it for you with their hydraulic stretcher. The cheap tubing expanders that you can get from Harbor Freight are designed to remove the small dents caused by old style muffler clamps. While they might expand a tube, you risk destroying the tool and it can be quite a time consuming job, even with an impact wrench.

I decided to just open up the small end by grinding it back into the angled section, where the OD gets larger. The downside to this is that you end up with two short stubs of pipe extending into the can, which will slightly affect airflow through it.

Here is the tubing, showing the OD (it’s not what I would call a 2.5 inch tube… ;) :


Here is the small downstream end of the resonator, showing how much material must still be removed:


Gradually remove material until the inner diameter started to enlarge. I used a bench mounted belt sander to keep the end true and flat, but if there are any flaws, they will get filled in and covered by the weld. Dress the ID using a large grinding stone to remove the burrs and then measure the hole. Repeat as needed until you get a nice snug slip fit. You can use the 12 inch cut section for testing:




Here is the rear section of tail pipe next to the prepared hole in the resonator:


And the rear section slid into the resonator. Cool!:


Now the front section. It already has the correct inner diameter (mine was actually a little too loose) so it just needs to be cut down, dressed smooth and made ready for the final fitting of the inside pipe.

Install the complete assembly onto the truck and bolt it tight. Push the resonator as high as possible while checking that the tip is slightly below 90 degrees with the ground to allow for condensation drainage. I used a six inch bubble level, comparing the tip angle against the rear bumper. Note that the two cut ends go WAY inside the resonator. You need to cut off the excess for a couple of reasons:

The front section might be deep enough that it blocks the flow into the outer spirals.

The rear section might block the airflow out of the muffler.

Neither situation is good for smooth airflow, so mark the ends of the resonator with a Sharpie, all the way around at both front and back. Remove the assembly and take it apart:


See how much extra there is, especially up front? Mark two new cut lines with masking tape, leaving short stubs to go into the holes – about ¾ inch. Don’t go much less than this or you may run into problems with the final fitting. Cut and dress the pipes:


Here’s the assembly ready to hang and weld:


Here is the tail pipe installed with an extra support to allow me to drive it to the welder. If you have to drive more than a few miles, or over bumpy roads, add a second support behind the resonator – you can wrap it around the frame using a similar setup to the front one. The main thing is to not lose that shiny resonator on a busy street when the rear bolt gets loose and the rear part rotates back and down!



It’s very unlikely you will find a muffler shop that can weld stainless – I called a few here in Spokane, and all of them told me to find a specialty speed shop or a welding shop. I have a local guy that I use for small welding projects. He put my truck on his lift and tacked the parts together, and then I removed the assembly from the truck for final welding. I took off the temporary support while he was welding, then reinstalled the finished pipe and came home.

More to follow.

John Davies
Spokane WA USA
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The angle of the tip changes with this mod – it now angles rearward slightly. If you were willing to re-make the rear mount, you could keep it at 90 degrees, but it would stick out further:



But is still tucks up nicely and it looks sexy:


BTW – some of that is red Moab dirt underneath – it’s not THAT rusty.


Driving impressions:

The exhaust note falls between the sound of the open pipe and the restricted pipe. It has a deep rumble that is not obnoxious under heavy throttle. It has a really nice, deep, reasonably quiet burble at idle. At cruise speeds around town it isn’t noticeable, but you definitely hear it under heavy throttle. On the highway at 2000 rpm it fades into the background. I have new door and window seals, so my truck is pretty quiet inside. If yours leaks air, you may find that this system is still too loud. With the windows down, it’s pretty noisy at all times.

I suspect the sound will be a little wearing when driving steep mountain grades with long periods of heavy throttle. Hopefully I will get used to it.

I tried getting some sound clips, but my MacBook microphone doesn’t do well with louder sounds and the results were disappointingly distorted. My feelings are that sound recorded by a cheap mike doesn’t really do much to tell you what a system sounds like.

The snappy feel is back, the truck seems to have the same power as the open system! I have zeroed my Ultra Gauge and will report the mileage change, if any.

My score: 4 stars, difficulty rating three bananas, because it takes so much fussing to install, and it does take some good mechanical skills and special tools... This is the way the optional system from EMS Powered should come!

John Davies
Spokane WA USA
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Seems like you need more muffler in the middle. If you compare the muffler on your system to the size of the stock muffler. Most aftermarket mufflers don't have enough volume inside really bring the noise level down. You can either get restrictive like stock mufflers or get more internal volume to lower the sound frequency of the noise. A turbo will really knock the edge off that noise. :)
A turbo muffler?? As a resonator or to replace the main muffler??
@ John E Davies

Are the internals of the Moroso made of Stainless?

Now that You've run it a while, how are you liking the Moroso?
Bump for Davies' thoughts on his Moroso Spiral Flow addition.
... have new door and window seals...

John - why did you go with new seals
- are these all around - 4 doors and rear as well?
- where existing seals (doors or seals) old/brittle
- what cost?
- how much noise reduction (on hwy) did you notice
- did you do door seals or windows seals separate (to compare noise reduction)
- easy enough to change

bit closer to you know that before (was in Colorado) but still a wee drive x the mths. If I'm over that way I'll ping you

Bump for Davies' thoughts on his Moroso Spiral Flow addition.

Sorry for the delay...... I still like this setup. It is a little loud on long trips, especially where there are lots of mountain grades. But the tone smooths out and becomes significantly less irritating at higher revs (over 3000). So I tend to manually downshift and let the engine rev in second on long climbs rather than letting it stay in 3rd, and the exhaust note is more pleasing.

I still recommend the Moroso.

John Davies
Spokane WA USA
John - why did you go with new seals
- are these all around - 4 doors and rear as well?
- where existing seals (doors or seals) old/brittle
- what cost?
- how much noise reduction (on hwy) did you notice
- did you do door seals or windows seals separate (to compare noise reduction)
- easy enough to change

bit closer to you know that before (was in Colorado) but still a wee drive x the mths. If I'm over that way I'll ping you


I was having lots of wind noise, especially from the sunroof on breezy days (say heading into a 20 mph headwind at 70 mph).

The sunroof seal is made onto the glass and is unavailable separately. I tried shimming the worn seal using a long strip of rubber cut from a bike inner tube, but it really didn't help much. I hate sunroofs with a passion (I will never buy one if I have a choice), so in the end I glued the panel shut and disconnected the motor connector. A new glass is US$400+.

That reduced the wind noise significantly, but I knew my front window seals (felt tracks) were shot, since the glass would rattle when part way down, and the door seals had obviously hardened.

I replaced the window felt tracks and lower trim moldings, inside and out, on both front windows. Now the windows don't rattle when part way down.

I replaced the door seals on all four doors plus the rear hatch (two pieces).

I rarely operate the rear passenger windows and never the sliders, so I decided to skip them. They seem to seal pretty well. I may do them at some future time.

Cost was about $585 from cruiserdan. There are no aftermarket seals available. It's a lot of money, but it made a HUGE difference in the NVH of the truck. With the windows up it was much quieter with less wind noise and the tires were more muted. Since we use this truck for long vacation road trips (3000+ miles), it was important to me to keep the interior noise down so we would not feel blasted after a ten hour day.

I didn't have any problems changing any of the seals, but I have been doing stuff like this for 40 years..... The door trim panels come off very easily. You have to remove the mirrors to get the outside lower rubber trim piece off. Getting the new felt seals down into their grooves is a little finnicky - but you can run the window up and down while applying downward pressure and they will get sucked into place.

My recommendation is that if you use your truck for long trips, do it. A truck that is used locally and with the windows down is not a good candidate.

John Davies
Spokane WA USA

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