Quieting it down - Moroso Spiral Flow Muffler

[Def]

So my S13 has been my daily driver lately while my E36 M3 is being repaired(some asshole failed to yield and hit me while turning left). It is just frankly too loud with a Megan Racing catback and a resonated test pipe. I've gotten black flagged at HPDEs as well, so I figured this would be a good time to get it a little more civilized.

I didn't have space to put in the usual 5x8x14" Magnaflow muffler underneath the car, and I didn't feel that going a little bigger than the MR 6" round x 14" long cannister in the back was going to get me much, so I decided to take a gamble with a Moroso Spiral Flow. It works by having a hollow core section and a spiral twist on the outer perimeter. The idea is that the sound waves travelling on the outside spiral travel a farther distance than the ones going straight through the ~1.25-1.5" ID straight through center section.

I was concerned with excessive pressure drop with this design, but the low weight and 4" round x 12" body dimensions enticed me so I ordered one from Summit.


I like having numbers, so I decided to check it out for myself.

Graph:

http://lh3.google.com/jfannon/R366bMz8uaI/AAAAAAAAADI/E8w-l53v7ks/s800/SpiralFlow.JPG


Rough rule of thumb is that about 1 lb/min of air = 10 rwhp. Fuel is added to the intake air as well so you get a higher mass flow in the exhaust, but for the purposes of a rough idea this is good enough. So about 0.75 psi of pressure drop through the Spiral Flow running about 300 rwhp. Now at a higher temperature(like in your exhaust), you'll have a lower density, so a higher velocity and more pressure drop for the same mass flow. The mass flow function (Flow * sqrt(Tabs) / Ptotal) dictates this happens at the square root of the absolute temperature, which is about double of this test(~530 deg R vs. maybe 1100 deg R post downpipe).

The other side of the coin is that as you increase pressure to deal with this drop in density due to temperature, you gain back density due to pressure causing air molecules closer together. That said - short story is that a very rough idea of pressure drop through this muffler is maybe 0.9-1.0 PSI at 300 rwhp.

About what I expected, and I don't see it making a huge difference in power. Keep in mind a straight pipe will not have zero pressure drop either, and the perforations in a "straight through" design do cause more pressure drop than a straight pipe as well. I think I recall most "straight through" 3" catbacks giving about 2-5 psi of pressure drop in the usual power ranges(more than 200 rwhp, less than 450 rwhp sounds reasonable).

I like putting numbers to theory, so I hope some other people get something out of this.

I'll have the spiral flow in next Friday, and I'll let everybody know my seat of the pants impressions.

[ckcadavona]

I plan on doing a custom 3 in. exhaust with two mufflers. Let us know how everything goes.

[snickers]

i had 2 of the 4" ones on my g20 back in the day when she was boosted. almost dead quiet at idle. I would deff buy and run these again for sure.

[90kacoupe]

im not sure how great it will be on performance... but i built a cat/resonator peice... i gutted a cat and welded a pipe, with a bunch of holes drilled in it, in the cat... it helped quit a bit on the sound.

[Steve_S14]

some useful information on freeflow and other types of mufflers

http://autospeed.com/cms/article.html?&A=0381&P=1

[Def]

I've had this on for about a week now, and did an autox/time trial with it and things were MUCH improved sound level wise. Everything is much quieter, and the spiral flow really took out a lot of the BOOM. It actually seems to quiet things down MORE when you go WOT vs. a cruise. Makes much more of an "air rushing out" noise with a little engine sound vs. before where it sounded almost like a pissed off sport bike at 140 dB and a little turbine sound thrown in.

A side benefit, I now have mucho compressor/turbine sounds where before it was just a slight hint of compressor sound but TONS of exhaust noise. It makes a rather pleasing turbine whine under partial throttle and about 0-5 psi if I do say so myself.

My clutch now slips after some high boost E85 action, so I've been keeping it at 14 psi or less, but there doesn't feel like any reduction in power at the lower boost levels. Boost comes on at exactly the same place from what I can tell, and if anything, by not going deaf at low boost levels the car seems much quicker around town since my ear drums allow me to give more than about 10% throttle putting around town.


All in all - I give it a huge thumbs up. I've never heard a straight through muffler make near this much of a difference in sound level.


Word to the wise for anybody installing one - one end IS a slip fit. I had to slightly muscle mine over the pipe, but this makes it pretty easy to fit it into an existing exhaust since you've got quite a bit of play at the slip connection.

[Epstein]

...by not going deaf at low boost levels the car seems much quicker around town since my ear drums allow me to give more than about 10% throttle putting around town.

All in all - I give it a huge thumbs up. I've never heard a straight through muffler make near this much of a difference in sound level.


+1 I'm glad you got things sorted out.

This is the same experience I had when I put a glasspack on my external wastegate dump tube. It's insane how much of a difference a little bit of muffler can make.

[WilloW]

That is great news! I'm going to order one, thanks for posting your review.

[98koukile]

I was very interested to see how these things performed on an import motor. The only other exhaust I still what to see someone try is the hooker aero chamber

[rennen]

I've had one of these on my NA KA24DE for 3-4 years now. All I have is a 3" catco cat and a 2.5" spiral flow resonator. It's loud, but the upper rpms sound great. I have a resonance at 2.5k rpm, but that's expected when hacking together an exhaust from scratch.

Here's some pictures (from along time ago) I realize it's not ideal, but it's better than the rusted out system I had before, and cost me less than $150 total:

http://photos-a.ak.facebook.com/photos-ak-sf2p/v295/192/123/15926474/n15926474_39290424_6108.jpg

http://photos-h.ak.facebook.com/photos-ak-sf2p/v295/192/123/15926474/n15926474_39290423_5785.jpg

http://photos-g.ak.facebook.com/photos-ak-sf2p/v295/192/123/15926474/n15926474_39290422_5430.jpg

[turtl631]

Pretty cool post. I may have to get one of these myself. NA KA with header and an exhaust flange leak is terrible, so the turbo SR setup I'll have in the car soon will be a big improvement, but I'm sure even that will be loud (I've got an SSAC 3" exhaust).

There's some kind of resonator in the piping and then the standard N1 muffler. I scraped a hole in the resonator when my car was dumped and I lived in an apartment complex with speed humps, so I can cut it out and just replace with the spiral flow. Then I'll be able to cruise around with the windows down again, and good thing, because the A/C is going out when the SR is installed.

[WilloW]

Holy freaking thread revival! I've just got the 3" ID version of this muffler, hopefully this will quiet down the RSR EXMAG (no resonator). I'll snaps some pictures and hopefully record sound clips of before and after for you guys.

[a_ahmed]

thumbs up for quality videos with sound :P

[2Fass240us]

Holy freaking thread revival! I've just got the 3" ID version of this muffler, hopefully this will quiet down the RSR EXMAG (no resonator). I'll snaps some pictures and hopefully record sound clips of before and after for you guys.I had mine welded in before my event a few weeks ago:
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/Exhaust/muffler_01.jpg
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/Exhaust/muffler_03.jpg

I wish I would've done it earlier...it made a pretty big difference throughout the rev range, including idle. The main driver was that the local autocross guys are starting to enforce dB limits, but it makes practical sense too.

[WilloW]

"2Fass240us", that's nice! Did your came shiny like that? Mine is just painted dull black. http://photos.freshalloy.com/gallery/d/41555-2/DSCN0036.JPG
http://photos.freshalloy.com/gallery/d/41552-2/DSCN0035.JPG
http://photos.freshalloy.com/gallery/d/41549-2/DSCN0033.JPG
http://photos.freshalloy.com/gallery/d/41546-2/DSCN0031.JPG

Now I'm having second thoughts about hacking up my RSR EXMAG to weld this thing on, but then I'm pretty convinced now that it will quiet it down tremendously.

[Def]

There is a stainless steel and a mild steel version. You got the mild steel version(it's what I have too). The SS version is about double the cost of the plain jane one.

[2Fass240us]

Jacob beat me to it. That is the difference. I ponied up for the SS one because the rest of my exhaust is SS.

[WilloW]

Yeah, I've got the mild steel version. If I knew I would've bought the stainless version. Is there anyway for me to treat this thing so that it doesn't rust to hell later on?

[turtl631]

I was planning on getting the mild steel one also. I have a stainless exhaust, but eh. Paint should keep it okay considering how little I drive the car.

[2Fass240us]

I was planning on getting the mild steel one also. I have a stainless exhaust, but eh. Paint should keep it okay considering how little I drive the car.You live in Chicago; pay the $50 extra.

[WilloW]

I've got a torch and some ATF, so I'm going to strip off the paint and do this to it.
Rust Proofing Mild Steel. (http://www.stockcarracing.com/techarticles/scrp_0808_tri_y_headers/index.html)

[2Fass240us]

Interesting article, and not a bad option since you've already purchased.

http://images.stockcarracing.com/techarticles/scrp_0808_14_z+rust_proof+install_ready_headers.jp g
Hey, what's that on the rotor? :D

[Def]

High temp paint is good. I'd get the SS one if I were driving on salted roads though.

[turtl631]

I don't drive in winter though. I'm not getting salt on these 8611 housings considering how much they cost.

[Cory]

How much of a power loss did any of you feel? Any trap speed/dyno/lap times/etc differences?

[2Fass240us]

I felt none. But my butt dyno isn't calibrated.

[a_ahmed]

http://www.xforce.com.au/cars/view_car/29

[WilloW]

http://www.xforce.com.au/cars/view_car/29

Thanks for posting that man, I'm on a quest to shut my car up so that's could be a good alternative.

For those that know of any good muffler with a dual tips, please visit my thread here --> "Help me shut my car up even more," (http://nissanroadracing.com/vbulletin/showthread.php?t=694)and help me out. I don't want to muck up Jacob's thread anymore than I already did.

[WilloW]

Jacob, I owe you a beer the next time I see you for this.

I finally got this thing welded onto my RSR EXMAG piping and it is QUIET! With a 3' Catco cat it sounds just a bit louder than stock but still quieter than a 350Z coupe. I'm so happy I got my sanity back. I just wished that I did this earlier.

[a_ahmed]

Revival of the dead, I need to shut the hell up my car too. The Dc Sports header and test pipe combination on a 2.5" na ka with an intake sound loud as *bleep*.

However its mostly been the dc sports 4-2-1 header... The car moves great and sounds great on track... but just not cop safe anymore :-/ It's not HONDA loud... but it has ****ty drone. From what I've been told my BRM exhaust is just a free flow magnaflow resonator (22") and muff (dualtip) ... which basically muffles jack **** and is more so for making power...

I was thinking of getting something custom built so at the testpipe section to have a bypass that goes straight open 3" when on track.... and at a flip of a switch some kind of exhaust that's quiet on the street....

I don't want to go back to the stock exhaust as its what like a mighty 70lbs or something ridiculous like that... but then i'm limited with options :-/

The varex stuff I've posted previously just might be something I'll consider trying...

[a_ahmed]

http://www.youtube.com/watch?v=-EfrV2MQU_g

[WilloW]

A_ahmed, just get yourself the Moroso pipe. and weld it inline of the BMR exhaust system you have right now. My RSR exhaust is 80mm and now its so quiet that its feels like I'm driving the wife's Accord. Most of what I hear now is the sound of air rushing out and the turbo spooling.

[a_ahmed]

well... i am non turbo :D But I'll give it a shot...

[Ruff Ryder 6]

i still wanna do this once i get my hands on a welder

[WilloW]

Do it! Just make you guys get the stainless version of the pipe instead of my mild steel version.

[Def]

I'm rocking the mild steel and it seems to be working fine. Coated with a nice layer of carbon, so that's my rust prevention. haha

[turtl631]

I was thinking of getting something custom built so at the testpipe section to have a bypass that goes straight open 3" when on track.... and at a flip of a switch some kind of exhaust that's quiet on the street....

Do your tracks have sound limits? 3" straight open on a NA KA is kind of a jackass move IMO, everyone will be expecting the car to haul ass when they hear it and then it'll be the slowest thing out there on the straights.

[WilloW]

I drove around with just a cat after the downpipe for a couple days for about 10 minutes each trip and it was absolute insanity (had no choice). Sounds like complete utter crap. It got to the point where the damn thing was so loud that it was painful to my ears as well as embarrassing to be so loud.

The only thing that was kind of neat about it was hearing the turbo while sitting at the light.

Don't do it, you'll kill your hearing.

[PoorMans180SX]

Yeah, I'm in need of a new exhaust.

I know a lot of you guys like your exhaust real quiet, but I enjoy a good throaty tone.

Do you think two of these in a 3in exhaust would have decent decibel levels? A little quieter than your typical "N1" exhaust?

[Scores240]

I have a 3" spiral flow waiting to get installed once i can drive my car again.
I have 3" straight pipe from end of stock headers into a magnaflow muffler at the end. After the test pipe it just got too loud and raspy. Oh N/A KA by the way.

I'll put up a video once i get it welded in.

[2Fass240us]

Do you think two of these in a 3in exhaust would have decent decibel levels? A little quieter than your typical "N1" exhaust?I would think you'd want to use one of these in the pipe and a chambered one at the rear of the car (assuming your exhaust exits there) for the best sound-damping. I will not even pretend to know what makes an exhaust "throaty," and thus cannot comment on the first part of your post.

[PoorMans180SX]

I would think you'd want to use one of these in the pipe and a chambered one at the rear of the car (assuming your exhaust exits there) for the best sound-damping. I will not even pretend to know what makes an exhaust "throaty," and thus cannot comment on the first part of your post.

Haha, I guess by throaty, I mean deep.

Basically all I need to know is if this muffler quiets your exhaust as much as the typical N1 straight through muffler. I've had an car with just an N1 muffler and I didn't mind it, just a bit too loud, so I was thinking 2 of these would do the trick. Trying to tuck my exhaust up into the car too because I'm really low, and these are a lot smaller than traditional mufflers.

Oh, the car will have a 2.5in cat in it too. (which my other car didn't)

[Def]

I have a 3" spiral flow waiting to get installed once i can drive my car again.
I have 3" straight pipe from end of stock headers into a magnaflow muffler at the end. After the test pipe it just got too loud and raspy. Oh N/A KA by the way.

I'll put up a video once i get it welded in.

Can you tell me if one end of the 1.5" center tube is flared? I might have installed mine backwards because it was done in a hurry at the end of 9 hrs of rollbar fabrication in 110 deg F Texas heat. Couldn't remember if the entrance is flared or not, as that would help the flow through there slightly.

[Scores240]

The small center tube is the same on both sides. Just looked at it. I don't think it matters what end is inlet/exit.

Although the outside 3" pipes are different on either end like ones bigger maybe slip fit like i heard somebody say.

[Def]

Yes, one is a slip fit on a 3" tube. Makes it pretty easy to fit. Just keep one side about 1-2" long and make sure the other is square.

[Solo_S14]

I drove around with just a cat after the downpipe for a couple days for about 10 minutes each trip and it was absolute insanity (had no choice).


lol, I drove my Maxima for a few weeks this fall with the exhaust cut off just in front of the rear wheel (from prior antics).

It was supercharged at the time, and essentially had a side exit exhaust with only a crappy muffler shop resonator after the cat.

It was utterly loud.....yet so awesome for a brief period.
:D

[Solo_S14]

Whoa, just realized this thread is 9 days old.
It's been sitting on my screen un-read since then.
haha