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03 H6 OBW & 06 WRX Sportwagon
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17,547 Posts
Discussion Starter #1
I'm pasting this in from something I saved months ago - thoughts?

Want to gain a few HP and several MPG?

Simple- Just remove the spring in the muffler bypass
valve and re-install it with the valve open. This reduces backpressure
and lets the engine breathe better.

This is on the left top side of the muffler, under a cap-like cover held
in place with three nuts. Remove the cap, and the spring is held
on with an additional nut. All are 10mm.

The shaft that the spring is on turns about 1/4 turn clockwise to open
it.

Put the spring back on so that if the valve goes to close, the spring
will hold it open.

Will it be louder?? Not much for local town driving. You can barely
tell
the difference from inside the car. If you stomp your foot down, you'll
hear it,
but it is not excessive.

A far as performance goes, throttle response seems better and gas
mileage
has gone from 22mpg to 26-27mpg on the highway for me.

This valve was supposed to open up when exhaust flow was great enough
to overcome spring tension, and bypass a section of the muffler.
If yours is like mine, you might discover that it is difficult to turn
by hand, probably never opening.

end paste

interesting!
 

SubaruOutback.org Founder
2018 Outback Limited 2.5L - 105,000+ miles
Joined
5,120 Posts
Sound neat, do you have pics for better modding and instruction? Is the bypass valve the little pipe on the side of the muffler by chance? If not, what the heck is that thing?

BTW, why bother opening it? I'd just tear it out with my appetite for destruction :22: Anyway I'll surely look into doing this, anything for a lil'extra performance! :D

Thanks!

Hey Peaty if you happen to read this, have your heard or know anything of this mod?
 

Registered
03 H6 OBW & 06 WRX Sportwagon
Joined
17,547 Posts
Discussion Starter #3
I should have been more clear - I haven't done this mod. I saved it from another forum. I do recall reading about this feature of the car. IIRC the little valve is supposed to open up at about 2400rpm. That would generally mean during acceleration or for extended highway speeds, there is a little more noise and a little less restriction - I guess. So this guy basically forced the bypass open all the time.
I just wondered if it was a well known mod. and if anyone else had tried it.
 

Lord of ScoobyMods, ,
19' Impreza Sport 5 dr / 01' Forester S / 13' OB CVT / 10' Legacy 3.6R / 99 Mita MX-5
Joined
1,213 Posts
Here is a pic of the bypass. I haven't messed with it myself as the OB is the wifes ride. She lets me do what I want to my F-XT so I don't complain :)
 

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SubaruOutback.org Founder
2018 Outback Limited 2.5L - 105,000+ miles
Joined
5,120 Posts
Thanks Peaty, that is what I was referring to beforehand. I had a guy at an exhaust shop look at it and he said he had never seen anything like it before on a muffler. Well I'll surely be decimating that thing here soon enough :22:
 

Registered
03 H6 OBW & 06 WRX Sportwagon
Joined
17,547 Posts
Discussion Starter #6
I wonder if those mufflers would fit the Imprezas?
 

Superb Moderator, ,
MY12 WRX, MY07 FXT
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6,186 Posts
What is it's intention, that alienlike apparatus on the muffler. That looks silly, get rid of it :4: Brian
 

Registered
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Hmm, do not recall seeing that on mine. Well, almost time for an oil change, will check it then.
 

Lord of ScoobyMods, ,
19' Impreza Sport 5 dr / 01' Forester S / 13' OB CVT / 10' Legacy 3.6R / 99 Mita MX-5
Joined
1,213 Posts
I have some specific info on it somewhere but can't seem to find it. What it is, is just a bypass that opens up when there is enough exhaust backpressure on the spring to open up the valve. It makes the exhaust more flow through.
 

Superb Moderator, ,
MY12 WRX, MY07 FXT
Joined
6,186 Posts
Kevin, too bad your muffler has so much corrosion already otherwise doing this mod would be easy. Now you run the chance of stripping those small nuts and such. Or you could soak 'em with penetrating oil and hope for the best! Brian
 

Superb Moderator, ,
MY12 WRX, MY07 FXT
Joined
6,186 Posts
Very nice, Peaty. Now the big question is how long does that spring last? I'm sure it gets corroded in there and quits working as it should in no time. Bypass that thing! Brian
 

Tokyo's between my toes
2001 Wintergreen Outback 5MT
Joined
6,684 Posts
- Wait, you mean your muffler bearings really can go out?
 

Lord of ScoobyMods, ,
19' Impreza Sport 5 dr / 01' Forester S / 13' OB CVT / 10' Legacy 3.6R / 99 Mita MX-5
Joined
1,213 Posts
bheinz57 said:
Very nice, Peaty. Now the big question is how long does that spring last? I'm sure it gets corroded in there and quits working as it should in no time. Bypass that thing! Brian
One would hope they thought of that and made the parts to be able to hold up.but who knows.
 

Registered
03 H6 OBW & 06 WRX Sportwagon
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17,547 Posts
Discussion Starter #15
those drawings don't make sense to me - but the concept does.
 

Tokyo's between my toes
2001 Wintergreen Outback 5MT
Joined
6,684 Posts
Looks like it allows the flow to skip past going through the center baffle when the valve is open.

Man, what is the price tag on one of those mufflers... looks like something Audi would come up with.
 

SubaruOutback.org Founder
2018 Outback Limited 2.5L - 105,000+ miles
Joined
5,120 Posts
I recently tried to perform this mod while changing my oil and they whole piece was rusted and corroded out. I broke one of the nuts off along with the end of the screw so I figured it would be too much more work to piss around with it. I would recommend that if you want to perform this mod you need to do it at a low mileage.
 

Premium Member
2016 Subaru Outback 2.5i Limited, EyeSight & Navigation (Wilderness Green)
Joined
170 Posts
Howdy, everyone! I'm new to posting on this forum but have been monitoring it for quite some time. I'm on my third Subaru Outback wagon鈥攁 '97 base model (5MT), to an '00 Limited (5MT), to an '04 L.L. Bean (4EAT)鈥攁nd have been totally satisfied with each of them. (As a point of reference, I'm coming from a background of SAAB's, Lexus coupes, and Toyota Camry's and compact 4x4 pickups.) No significant problems with any of the Outbacks (so far ... knock on wood!), actually no minor problems, either.

I wanted to let you guys know that I performed this muffler bypass valve modification today (wanted to try it while the nuts on the bypass valve spring cover are still relatively easy to remove). I haven't had a chance to test it out since we're in the midst of a severe Winter storm. With just a little under 3K miles on this vehicle my fuel economy (roughly 70% highway, 30% city) has been ranging between 20 and 22 MPG. I will be keeping tabs on it further to see if the modification has any real effect and will pass on any observations. There doesn't seem to be much of a difference in the noise level. I'm also running Amsoil 5-30W in this engine (I've been using synthetics since 1980).

Does anyone know where this modification originated? I'm wondering if there's been any additional information from the originator or other personal experiences with it. Thanks in advance.

Cheers ...
 

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2002 LL Bean (H6)
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Very good peaty! My '02 LLBean Has 93,000 miles, and the valve still opens, & closes ok (stainless). It's effects are really noticeable above 4000 rpm. I'm gonna lock mine open to see if it helps with low-end torque for hauling the boat. Will let you know. It's my wifes car, but we're from the'60's (drivers) when louder cars were Nice!!! (Not the "Fast & Furious" buzz-bombs of this century.
Thanks, Larry.
 

Registered
06 OBW 2.5, 05 Forester, had 03 H6 OBW
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5,927 Posts
This is the most recent thread on this muffler goober I've found so far-

When I get a chance I think I'll try it, because this is the kind of gimmicky thing that works for a few years then seizes solid.

I wonder what it would sound like (with the bypass working normally) if you dumped it into a little pipe of its own, instead of back into the muffler?


Dave
 
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