How to make 400+whp quieter?

I'm running a 3" catless with two resonators and avo mufflers. I know my AVOs are the best sounding mufflers made for the outback but even with my two tube style resonators welded in to the 3" mid pipe I still get dirty looks when I drop my kids off for school in the morning.

I am wondering if I can put the stock mufflers back on and not lose any performance. I'm running a 53/lb min turbo. (efr 6758). I'm hoping since we have dual exhaust my 3" Y pipe will make the stock mufflers doable without a performance hit.

Mods move this to the exhaust thread if you need to. It seems the main forum is where all the eye balls are anyway.

Not having children will greatly improve your ability to save, give you more free time, and have a tremendously larger impact on the environment then my exhaust. But I'm not selling condoms to anyone.

If it doesnt give me a performance hit I'll put on a cat for sure, even if its down stream to give the exhaust time to cool.

Here's my experience from my other car. It's an EJ207 that revs to 8K, and a Dom 3 XTR. The whole turbo setup, with it being on a small displacement motor, is dependent on exhaust flow. My exhaust is a custom straight 3" exhaust (internal wastegate, no resonators) with a Varex muffler at the back. If you're not familiar, the Varex muffler is the kind of muffler that has a butterfly inside that bypasses the muffler section. Essentially, it's a cutout inside of a muffler. When it's open, it's 3.5" straight through, when it's closed, it's like a stock muffler. The cutout is controlled by a motor on a button that you have to hold to open all the way, like a window. So you can stop the opening action at any point in between fully open and fully closed. When it's fully closed, it's quiet like stock, with it open, it sounds like open headers. Half-open seems to be equivalent to the sound of a common, catted turboback.

Here's what I've observed: When it's open, I spool to 25psi at just over 4K. When it's fully closed, it takes the full rpm range to sloly build to 10psi. Actually, I don't know if I've ever run it to 8K with it fully closed, but up to 6.5-7K, it still doesn't break 10psi. With it half open, it spools to the teens, say 13-15psi, baround 5.5K.

None of that is surprising, as a large turbo on a small motor lives and dies based on exhaust velocity. What I was surprised by was how much the exhaust sound correlated to the performance. In other words, if you want it quiet, it's going to choke it. It doesn't matter if the choke point is under the rear bumper or right behind the turbo. Wherever the choke point is, is going to get really hot. So you can sort of just feel the pipe after a drive, and see where the hotspots are, and that's where your backpressure is. I've also found, while experimenting with building my exhuast, that since it's a closed system, it doesn't matter if you have a cat in the front or under the bumper, as long as it's in there, it's going to choke, so it'll get hot. The difference of a couple feet isn't going to turn 1400* exhaust into 900*exhaust.

My point here is that using basic components, as long as you quiet it down, you'll beb slowing down exhaust velocity, hich will result in decreased performance. Now there might be clever technologies out there that specifidcally combat these principals like magic mufflers that maintain exhaust flow while also decreasing DB, or resonators that change the resonant frequency of the exhust, so it drones at a less obnoxious tone. But generally speaking, on a turbo car, loud equals power. Quieter on the same car will almost always result in less power. It makes less of a difference if you were runing low boost on a big motor, (like 7psi), but since you're on a 2.5L, my guess is your boost is in the 20's somewhere. Sorry for the super long ramble.

Here's my experience from my other car. It's an EJ207 that revs to 8K, and a Dom 3 XTR. The whole turbo setup, with it being on a small displacement motor, is dependent on exhaust flow. My exhaust is a custom straight 3" exhaust (internal wastegate, no resonators) with a Varex muffler at the back. If you're not familiar, the Varex muffler is the kind of muffler that has a butterfly inside that bypasses the muffler section. Essentially, it's a cutout inside of a muffler. When it's open, it's 3.5" straight through, when it's closed, it's like a stock muffler. The cutout is controlled by a motor on a button that you have to hold to open all the way, like a window. So you can stop the opening action at any point in between fully open and fully closed. When it's fully closed, it's quiet like stock, with it open, it sounds like open headers. Half-open seems to be equivalent to the sound of a common, catted turboback.

 

Here's what I've observed: When it's open, I spool to 25psi at just over 4K. When it's fully closed, it takes the full rpm range to sloly build to 10psi. Actually, I don't know if I've ever run it to 8K with it fully closed, but up to 6.5-7K, it still doesn't break 10psi. With it half open, it spools to the teens, say 13-15psi, baround 5.5K.

 

None of that is surprising, as a large turbo on a small motor lives and dies based on exhaust velocity. What I was surprised by was how much the exhaust sound correlated to the performance. In other words, if you want it quiet, it's going to choke it. It doesn't matter if the choke point is under the rear bumper or right behind the turbo. Wherever the choke point is, is going to get really hot. So you can sort of just feel the pipe after a drive, and see where the hotspots are, and that's where your backpressure is. I've also found, while experimenting with building my exhuast, that since it's a closed system, it doesn't matter if you have a cat in the front or under the bumper, as long as it's in there, it's going to choke, so it'll get hot. The difference of a couple feet isn't going to turn 1400* exhaust into 900*exhaust.

 

My point here is that using basic components, as long as you quiet it down, you'll beb slowing down exhaust velocity, hich will result in decreased performance. Now there might be clever technologies out there that specifidcally combat these principals like magic mufflers that maintain exhaust flow while also decreasing DB, or resonators that change the resonant frequency of the exhust, so it drones at a less obnoxious tone. But generally speaking, on a turbo car, loud equals power. Quieter on the same car will almost always result in less power. It makes less of a difference if you were runing low boost on a big motor, (like 7psi), but since you're on a 2.5L, my guess is your boost is in the 20's somewhere. Sorry for the super long ramble.

This was great information! Keep rambling it was all great. I'm at 26 psi.

I'm thinking a boost activated cutout might be the next thing I consider.

I cannot think of anything to make it quieter other then...

Chambered mufflers (will hurt performance), but WILL quiet it down the most. (at most maybe 30 flywheel horsepower lost?)

And/or add a resonator (or two). I do not believe it will turn the decibels down a lot, but often makes it more "mellow" and eliminates harsh notes.

I have a Cobb catted downpipe, and I believe with the filtration size it won't quiet it down much if you went to a cat. On my turbo V8's I would never run a cat, but would not run catless on a vehicle I drive more than 3 or 4 times a week.

I think turbo vehicles are relatively quiet, due to the spin enforced on the air exiting the turbo? Sometimes just because something is 'low and bassy' it seems very loud.

Within the human ear high frequencies are stimulated closest to the eardrum and as the pitch lowers, its stimulated deeper into the cochlea.

Which is why I think it is "interpreted/felt" as louder just because it is 'lower.'

After asking the audiologist fiancee she says I am wrong. So be it, I'd rather hear an EJ motor than a raging bumble bee....

I cannot think of anything to make it quieter other then...

 

Chambered mufflers (will hurt performance), but WILL quiet it down the most. (at most maybe 30 flywheel horsepower lost?)

 

And/or add a resonator (or two). I do not believe it will turn the decibels down a lot, but often makes it more "mellow" and eliminates harsh notes.

 

I have a Cobb catted downpipe, and I believe with the filtration size it won't quiet it down much if you went to a cat. On my turbo V8's I would never run a cat, but would not run catless on a vehicle I drive more than 3 or 4 times a week.

 

I think turbo vehicles are relatively quiet, due to the spin enforced on the air exiting the turbo? Sometimes just because something is 'low and bassy' it seems very loud.

 

Within the human ear high frequencies are stimulated closest to the eardrum and as the pitch lowers, its stimulated deeper into the cochlea.

Which is why I think it is "interpreted/felt" as louder just because it is 'lower.'

 

After asking the audiologist fiancee she says I am wrong. So be it, I'd rather hear an EJ motor than a raging bumble bee....

Moar mufflers!!

I used to run AVO catted dp, Perin midpipe w/resonator and Prodrive muffers. Was loud and drony.

I replaced the resonator with a straight-through Magnaflow muffler. No power loss to speak of and WAY QUIETER.

Moar mufflers!!

 

I used to run AVO catted dp, Perin midpipe w/resonator and Prodrive muffers. Was loud and drony.

 

I replaced the resonator with a straight-through Magnaflow muffler. No power loss to speak of and WAY QUIETER.

This is interesting. I'm i'm in the same boat as xtea. My GS catted down pipe, resonated HKS mid-pipe, and HKS mufflers are loud for my taste.

I considered the cutout option but don't really want the straight pipe sound when WOT.

Replacing the resonator with a muffler never really crossed my mind but if you can do it with zero power loss it could be ideal.

Thoughts I am thinking.

I want the best of both worlds. I do not want to have a loud a$$ car whenever I hit the gas. I'd like to keep the sound level I have now for WOT and driving around town. But when I start up in the morning have a quieter option.

So what if I had a valve at the Y pipe? This way I could select a different muffler with a switch. Have the stock muffler on one side for start up and then flip the switch for the avo muffler. In addition I wonder if having one exit pipe at a time might help keep the sound down instead of having two. Also I think there may be more room for a diverter near the y pipe. My only problem them is finding a corrosive and water resistant way of installing it.

You are overcomplicating it. My car is still pretty loud at WOT.

If you want loud then install a cutouts before rear muffler(s).

I think he and I want the same thing.

A cutout will not provide the same sound he currently has with the AVO mufflers. A cutout will provide a straight piped loud exhaust. (Which is exactly what turned me away)

Thoughts I am thinking.

 

I want the best of both worlds. I do not want to have a loud a$$ car whenever I hit the gas. I'd like to keep the sound level I have now for WOT and driving around town. But when I start up in the morning have a quieter option.

Like mentionned above : Varex mufflers

Sounds isn't the greatest but it gives a good idea.

I'm not shy to start my car in the morning now.

[ame=http://www.youtube.com/watch?v=eQ3TkOH6CGA]Subaru LGT Varex soundclip - YouTube[/ame]

The video was made with my previous LGT.

It is currently on my OBXT, it just needs extended tips and a bumper trim to cut drone since the tips are couple of inches short.

Problem is they are expensive. Especially when buying two !! They come universal so the flanges must be fab.

Since fab must be done anyway, another option is doing a custom single exit CBE with only 1 varex can.

I'll try to make another video after my Tomei ELH install next week

On the varex topic:

https://www.summitracing.com/parts/xfo-vksb01?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-xforce&gclid=CjwKCAiA_ojVBRAlEiwAOLRxI2Hy2LMMJ1GpwEe47s3hizvyybuuYzcu1iqqJaEfTX5LiX3hwklbxRoCqSEQAvD_BwE

This is interesting. I'm i'm in the same boat as xtea. My GS catted down pipe, resonated HKS mid-pipe, and HKS mufflers are loud for my taste.

 

I considered the cutout option but don't really want the straight pipe sound when WOT.

 

Replacing the resonator with a muffler never really crossed my mind but if you can do it with zero power loss it could be ideal.

Have you tried the HKS cans with a stock mid-pipe? Curious to see what you think of the difference.

I have never had a stock mid-pipe. I assume that is 2.5" I also assume I'm getting into the area where anything below 3" will affect performance.

Performance comes first, but if I can have the best of both worlds.......

I'm running a 3" catless with two resonators and avo mufflers. I know my AVOs are the best sounding mufflers made for the outback but even with my two tube style resonators welded in to the 3" mid pipe I still get dirty looks when I drop my kids off for school in the morning.

 

 

I am wondering if I can put the stock mufflers back on and not lose any performance. I'm running a 53/lb min turbo. (efr 6758). I'm hoping since we have dual exhaust my 3" Y pipe will make the stock mufflers doable without a performance hit.

Stock catback measured at 4psi backpressure, at the start of the catback, with ~13psi of boost on my car.

Whats the can size of the resonators, 4"? What's the can length? Here is the secret to reducing exhaust noise, even on big 3-4" pipes. You need resonators and mufflers with a lot of internal volume.

At first I tried to use the 05 LGT muffler on my custom 3" single exit setup (with 5" Borla resonator). I bored it out to 3" entry and 3" exit, then removed the internal pipes that force are are very restrictive. It was a little too loud for my taste, but had only 1psi of back pressure (measured right where the catback starts, so it includes all piping restrictions too).

http://legacygt.com/forums/attachment.php?attachmentid=254304&stc=1&d=1503120834

http://legacygt.com/forums/attachment.php?attachmentid=254305&stc=1&d=1503120834

I then took the STI muffler from my other wrecked parts car, welded it to fit, it's MUCH quieter, probably 2-3 decibels less. Best of all, with this quieter muffler setup there was still only 1psi worth of back pressure.

Here is the size comparison of the STI vs stock LGT muffler. This picture doesn't do it justice because LGT muffler is basically a triangle, so it has a lot less internal volume

http://legacygt.com/forums/attachment.php?attachmentid=254306&stc=1&d=1503120834

I like when he gets all factual about things.

Makes me giddy all over!

Like mentionned above : Varex mufflers

 

Sounds isn't the greatest but it gives a good idea.

I'm not shy to start my car in the morning now.

 

The video was made with my previous LGT.

It is currently on my OBXT, it just needs extended tips and a bumper trim to cut drone since the tips are couple of inches short.

 

Problem is they are expensive. Especially when buying two !! They come universal so the flanges must be fab.

Since fab must be done anyway, another option is doing a custom single exit CBE with only 1 varex can.

 

I'll try to make another video after my Tomei ELH install next week

WHOA DANG! The bass when you open the valve is craaaaazy! It's like a subwoofer was flipped on. A huge one!

On the varex topic:

 

https://www.summitracing.com/parts/xfo-vksb01?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-xforce&gclid=CjwKCAiA_ojVBRAlEiwAOLRxI2Hy2LMMJ1GpwEe47s3hizvyybuuYzcu1iqqJaEfTX5LiX3hwklbxRoCqSEQAvD_BwE

That thing is expensive, but awesome!!!

"The Varex Exhaust Smart Box even has a Geo mode for those places where you need to be quiet. That's right you can set regions on a map that your exhaust will automatically stay quiet while in those regions. Multiple regions can be set and memorized by the app on your smartphone."

Single high flow cat, stock mid resonator swapped for a bullet style and stock cans.

Single high flow cat, stock mid no resonator and stock cans.