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Old 12-31-2010, 12:29 PM   #1
drewvdw
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Default muffler/cat bypass

has anyone ever run a seperate exhaust pipe by the cat and muffler (straight-pipe) but have it run off an electronically controlled butterfly valve? i was thinking about this and how much work it would take. it seems like it wouldn't be too difficult, with the exception of the butterfly valve (i can't quite imagine if it would work or not). this would be street legal...as long as you were using the stock exhaust...how ungodly loud would this end up being? and would it even sound good or just noise?
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Old 12-31-2010, 01:12 PM   #2
Web Foot STi
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Something like this?

http://www.xcceleration.com/itemdeta...83.htm#stealth

Getting a second pipe ahead of the cat could be a little tough...
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Old 12-31-2010, 03:34 PM   #3
drewvdw
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Quote:
Originally Posted by Web Foot STi View Post
Something like this?

http://www.xcceleration.com/itemdeta...83.htm#stealth

Getting a second pipe ahead of the cat could be a little tough...
bingo, we have a winner, thats exactly what i was looking for! but instead of keeping the catted dp, i would swap in a catless dp and cut the oem cat off the flanges and bends (so its just a straight piece), weld the flanges back on to the "new" cat, place that somewhere between the dp and muffler. i wouldn't forget to move any sensors as well. that way you could bypass it easier...would it be better to bypass them seperately or with one straightpipe? it seems like it could be more difficult to do it all at once, but cheaper and higher flowing as well...i gotta get under my car to see for sure...
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Old 01-01-2011, 01:47 AM   #4
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Interesting idea to say the least, make sure you post pics if you follow through
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Old 01-01-2011, 02:35 PM   #5
drewvdw
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i definately will if i end up doing it.
off topic, but you're from sioux falls? i'm from orange city, ia. if i end up doin it, you might have to listen to it.
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Old 01-01-2011, 07:01 PM   #6
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Quote:
Originally Posted by drewvdw
i definately will if i end up doing it.
off topic, but you're from sioux falls? i'm from orange city, ia. if i end up doin it, you might have to listen to it.
Sure, I'm also one of the owners of fastflat4.com we're planning on coming down to Iowa this summer for a couple things so I'm sure I'll see you around sometime
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Old 01-01-2011, 07:56 PM   #7
drewvdw
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great to know! i took a look at the website and noticed you are partners with speed techniques, thats where i had my car tuned. if you happen to be available May 19-21, it would be awesome if you and some other subie owners could show up for the car show, theres never any imports there. i'll talk to jared and dan about it as well. ps, i bought my car at sioux falls subaru through dan, showed up at speed techniques and thought he was stalking me, hahaha
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Old 01-02-2011, 10:26 PM   #8
sorrowfulkiller
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Quote:
Originally Posted by drewvdw View Post
great to know! i took a look at the website and noticed you are partners with speed techniques, thats where i had my car tuned. if you happen to be available May 19-21, it would be awesome if you and some other subie owners could show up for the car show, theres never any imports there. i'll talk to jared and dan about it as well. ps, i bought my car at sioux falls subaru through dan, showed up at speed techniques and thought he was stalking me, hahaha
Sound like a good plan to me, and yeah ha ha that's how it is up here. You see anyone with a subie and more than likely they have close ties with the people that either sell or tune them. PM me and I'll talk to my partner and see if we'll be able to make it.
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Old 01-14-2011, 06:56 PM   #9
xDRAN0x
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I was thinking of putting this on my 07 WRX, not sure I want to deal with the possibility of cops hanging out in front of my tailpipe

http://www.quicktimeperformance.com/QTEC/index.php
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Old 01-15-2011, 05:55 AM   #10
Kfly04
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wouldn't a butterfly valve sound like a external wastegate when it functions? Loud!?
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Old 01-15-2011, 08:42 AM   #11
drewvdw
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well, it would just change where the exhaust is flowing, instead of flowing through the cat and muffler, it would go straight-pipe at the flip of a switch, so yes, it would be very loud
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Old 01-15-2011, 06:22 PM   #12
mxracer88
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A friend of mine build an exhaust for my evo with somewhat the same concept, but still passes through the muffler. When you are off the turbo and just cruising the butterfly valve is closed, but as soon stomp on the throttle and want to go it diverts the gas follow through the 3" pipe passing the cat.


Last edited by mxracer88; 01-15-2011 at 06:28 PM.
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Old 01-15-2011, 06:49 PM   #13
drewvdw
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Quote:
Originally Posted by mxracer88
A friend of mine build an exhaust for my evo with somewhat the same concept, but still passes through the muffler. When you are off the turbo and just cruising the butterfly valve is closed, but as soon stomp on the throttle and want to go it diverts the gas follow through the 3" pipe passing the cat.
So you had it hooked up to the tps sensor? I personally wouldn't do that because it would be a bitch to try to tune that, id just go with a toggle switch, but that's just me. Looks good though!
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Old 01-15-2011, 11:41 PM   #14
P4radigm
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Quote:
Originally Posted by mxracer88 View Post
A friend of mine build an exhaust for my evo with somewhat the same concept, but still passes through the muffler. When you are off the turbo and just cruising the butterfly valve is closed, but as soon stomp on the throttle and want to go it diverts the gas follow through the 3" pipe passing the cat.

Your friend has some awesome welding and fab skills.
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Old 01-26-2011, 01:23 PM   #15
imma_stocker
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Quote:
Originally Posted by drewvdw View Post
has anyone ever run a seperate exhaust pipe by the cat and muffler (straight-pipe) but have it run off an electronically controlled butterfly valve? i was thinking about this and how much work it would take. it seems like it wouldn't be too difficult, with the exception of the butterfly valve (i can't quite imagine if it would work or not). this would be street legal...as long as you were using the stock exhaust...how ungodly loud would this end up being? and would it even sound good or just noise?
This part made me laugh. A straight pipe is not street legal in any way shape or form. You will probably meet emissions and exhaust db restrictions while closed but any modifications before a cat is technically illegal, hence the 'off-road use only' disclaimer on downpipes and exhaust manifolds.

When you open it up your car will sound like any other catless subie with similar mods.

Not trying to discourage you but this is misleading info that might get someone else in trouble if they cite NASIOC to authorities
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Old 01-26-2011, 01:31 PM   #16
drewvdw
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Default

well yeah, i know that catless is illegal, but i was wondering if the bypass itself would be illegal if you said it was used as a track day car and i would hook it up to a manual switch rather than the tps sensor
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Old 01-27-2011, 03:41 PM   #17
mxracer88
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Quote:
Originally Posted by drewvdw View Post
So you had it hooked up to the tps sensor? I personally wouldn't do that because it would be a bitch to try to tune that, id just go with a toggle switch, but that's just me. Looks good though!
No the TPS sensor is not hooked up to the exhaust. The butterfly valves open and closes by a spring. When you are out of the turbo there isnt enough pressure with in the exhaust system to direct the flow through straight pipe, when you you throttle on the spring is compressed allowing the exhaust fumes through the straight pipe.
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Old 01-27-2011, 05:42 PM   #18
drewvdw
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ahhh, i see
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Old 01-27-2011, 05:47 PM   #19
mikeydrives1
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I have a friend i used to work with who has an electric cutout just after his DP on a 2003 WRX. It sounds pretty nasty when he opens it ( has stock axleback system on)
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Old 01-27-2011, 05:59 PM   #20
drewvdw
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nasty as in good nasty or bad nasty?
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