Best route to fix the exhaust rasp? - Ford Mustang Forum
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post #1 of 21 (permalink) Old 11-09-2013 Thread Starter
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Best route to fix the exhaust rasp?

I've done a lot of searching, but I'm a bit confused about what I can do with my exhaust setup. My car is currently under warranty, so I can't do an O/R X or H pipe (I think? According to a dealer rep). I currently just have an Airaid intake and Roush axle-backs, but I'm still really bothered by the amount of horrible rasp around 3k RPMs. I've heard you guys talk about resonators of different lengths fixing the rasp, but I don't know what to take to my muffler shop to get this problem fixed once and for all. I wouldn't even bother with this, but with this engine and a 2.73 rear end I really can't avoid the 3k RPM range in normal daily driving. So every time I open it up I have to hear that really ****** rasp before the engine really screams. Can anyone possibly spare me a straight answer on what I need to bring the exhaust shop to get rid of this? I would really appreciate it if anyone could put in laymen's terms what causes and what would alleviate my exhaust issues!


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post #2 of 21 (permalink) Old 11-09-2013
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Sheesh! Just take the Roush exhaust off and put the stock mufflers back on.


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post #3 of 21 (permalink) Old 11-09-2013
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Quote:
Just take the Roush exhaust off
this. or put gt 500 axle backs on - some ppl claim a bit of rasp with Roush

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post #4 of 21 (permalink) Old 11-09-2013 Thread Starter
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I love the sound and especially the volume of the Roush mufflers and I'm definitely keeping them. I've had them on the car since 200 miles. I just want to figure out what I can do about the 3k RPM rasp...

EDIT: Or if it's the Roush mufflers causing this, I'm ok with selling them and switching to another brand. I really love how loud they are and the vibrations they make within the car. It's just that little bit of rasp that's been bothering me. If it were anywhere else in the powerband I wouldn't care at all, but 3k is unavoidable with this engine in daily driving.

Airaid CAI, Roush axle-backs, Roush high flow upper grill, Raxiom Smoked Projector HIDs
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post #5 of 21 (permalink) Old 11-10-2013
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It's a 60 degree V6, rasp is inherent in a free flowing exhaust on this engine.

And I could drive my 2.73 geared, manual, 2012 V6 all day without EVER going as high as 3000 rpm.

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post #6 of 21 (permalink) Old 11-10-2013
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The only thing inherent here is the Roush mufflers. IF you are getting rasp and you have the stock Cats, resonators and mid pipe (no off road x) and you got rasp with just those mufflers, its the muffler design. I say this because I have 3 setups on my car with the stock X pipe and cats etc and Rasp did not occur till an off road pipe was introduced and the cats and resonators were removed.

There are lots of ways to fix it this but if the mufflers are that way to begin with its gets tricky. You have to tune the exhaust and that often is trial and error. If you add more resonators which you can you will want to go greater than 12". 12" long 4" diameter resonators will cut a little rasp off the top, will reduce or eliminate the drone on the highway but will probably not remove what you want, you will want to go with a longer tube say 16 to 18" resonators or go with something like Vibrant ultra quiet resonators but you run into other issues going longer.

#1 room to weld them into stock pipes, 4" is about the comfortable diameter but only a couple spots they can be welded.
#2 length may not give you many choices where you need the sound tuned the most.

Best results are usually further away from the axle backs, but if room is tight then you will have to go just before the over axles.

Cheapest most effective way in your setup and this sucks, is to replace those mufflers they are so well known for being raspy, get a higher quality set of axle backs that work best with your setup out of the box.

Check out some other brands etc. Because your options are a pair of $100 good resonators, maybe another $150 to $200 to have them welded and you may find it did not even make a dent at the right wavelength.

Most of the posts and reviews of those Roush mufflers are the same, all rasp. Not bad sounding till you hit that register, even the V6 shelby review complained about it and from the video I can see why.
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post #7 of 21 (permalink) Old 11-10-2013
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At the local cruise in had a guy that had Roush mufflers on it, put on Vibrant Resonators because of the Rasp and they worked, but he also lost the sound. He ended up going with Borla S type which was louder than the Roush after the Resonators but not as loud as before them.

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post #8 of 21 (permalink) Old 11-11-2013
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Wonder where he placed them, that had an effect one the way the sound is tuned. Often if you place them further from the axles you will get more sound reduction, the closer you get you will loose less usually. You can see this with were the stock V6 places their resonators before the X as opposed to the GTs where they are placed after and almost middle of the mid pipe. Less distance from the mufflers.

From my understanding the length from where the wavelengths are slowed down, to where they exit has an effect on the sound output. But I also suppose that muffler design may also have a lot to do with it, if they are chambered no packing like MAC flowpaths or like Dynomax strait throughs with louvered cores and packing material you will get different results with resonators.

Chambered mufflers may get greater results with resonators over strait throughs. I do not know where the roush ones fall. never dissected those.
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post #9 of 21 (permalink) Old 11-18-2013
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I'm currently looking for a set of GT resonators the sound difference is much better with them I think. Will be glad to tone down the rasp.

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You should be shifting at 2k rpm but I know what you mean, I have the same exact setup.

I'd give these a try, I heard it helps;
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ive done a lot of research on this.

on our engine, rasp is mostly coming from the combination of 60 degree with an xpipe design.

what ive found that other cars have done to eliminate the rasp is one of these..



thats a magnaflow tru x muffler. think x pipe in a muffler.

you could put one after your x pipe, or alternatively, you could have an xpipe built with one

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Pretty certain that is one of our Ultra Flo Welded X mufflers. :yelpleased:

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Quote:
Originally Posted by cerebrix View Post
ive done a lot of research on this.

on our engine, rasp is mostly coming from the combination of 60 degree with an xpipe design.

what ive found that other cars have done to eliminate the rasp is one of these..



thats a magnaflow tru x muffler. think x pipe in a muffler.

you could put one after your x pipe, or alternatively, you could have an xpipe built with one
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lol whoops. i just google searched tru x. i wasnt aware there were a few of these out there.

ok so theirs too =p

the big thing, x in a muffler = no rasp

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No worries! I spent the last two days looking over our site and remembered that image. And you are right about the internal x-pipe. I have a lot of guys run this for space and a "dual" outlet option too.

A penguin gif?!?!?

Quote:
Originally Posted by cerebrix View Post
lol whoops. i just google searched tru x. i wasnt aware there were a few of these out there.

ok so theirs too =p

the big thing, x in a muffler = no rasp
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Has anyone had any experience with one of these in the 3.7? Or know of a video this has really got me interested.

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