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Old 11-19-2012, 12:36 AM   #1
subiedrivaa
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Default What downpipe to buy?

I want to buy an invidia bellmouth downpipe for my 03 WRX. Do i need to get one that has two o2 sensor bungs? or just one o2 sensor bung?
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Old 11-19-2012, 12:42 AM   #2
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just one unless ya want to run a wideband
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Old 11-19-2012, 02:31 AM   #3
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I'd just get the one with two. That way in the future if you ever want to add a wide band you can just pull out the plug and install it rather than having to weld on a bung at that point.

Joel
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Old 11-19-2012, 04:59 PM   #4
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Quote:
Originally Posted by CanadianImprezaSTi View Post
I'd just get the one with two. That way in the future if you ever want to add a wide band you can just pull out the plug and install it rather than having to weld on a bung at that point.

Joel
agreed its a pain had to do this sucks drilling and welding cast i took it to an exhaust shop and they 1st didnt drill the hole where i marked it so the sensor i put in rubbed on the firewall and second it was a crappy weld job took it to my friends dads house to weld it better lol just a pain get the one with 2 sensors they give u a plug for the second if you dont use it and if they for some reason they dont pm me i have like 5 of em lol
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Old 11-19-2012, 11:42 PM   #5
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I'd go with the Cobb one. I have a Perrin and then had to get an o2 drilled and welded. The first place told me they could do it and then they said they couldn't weld stainless. I like the idea of divorced wastegate, but I think bellmouth is just as good.
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Old 11-21-2012, 01:31 AM   #6
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Thanks. So what are the advantages to running wide band?
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Old 11-21-2012, 02:19 AM   #7
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Originally Posted by subiedrivaa View Post
Thanks. So what are the advantages to running wide band?

bein able to tune it properly
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Old 11-21-2012, 05:55 AM   #8
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Any 3in dp will work for ya. Not one (bellmouth, divorced, flat flange) provides any benefit. And if someone says it does.....ask them for proof of this.....u won't get any lol
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Old 11-21-2012, 06:49 AM   #9
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Originally Posted by shamrock 05 View Post
Any 3in dp will work for ya. Not one (bellmouth, divorced, flat flange) provides any benefit. And if someone says it does.....ask them for proof of this.....u won't get any lol
sweetie....there is all sorts of evidence out there if ya look around

but it aint k00.....

and most of the real 'gains' arent glaringly apparent on kiddie dynos anyway
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Old 11-21-2012, 08:11 AM   #10
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Originally Posted by Uncle Scotty View Post
sweetie....there is all sorts of evidence out there if ya look around
but it aint k00.....

and most of the real 'gains' arent glaringly apparent on kiddie dynos anyway



"The primary purpose of an aftermarket downpipe is to remove or replace the stock catalytic converter with a better flowing unit. It also increases the exhaust diameter for better flow."

"Which manufacturer is best? This topic is highly debated. There have been no reported consistent "bad" downpipes on the market. Obviously, there may have been bad pipes sold, but not enough to report as "bad" overall."

"Which downpipe construction method is best? Downpipes have 4 main construction methods:
1. Blank plate: Identical to stock construction with the wastegate portion completely covered.
2. Bellmouth: Completely open design.
3. Split bellmouth: Similar to bellmouth only with a divider inserted to separate the wastegate.
4. Divorced or Twin Dump: Separate exhaust and wastegate piping that connect further downstream.

There is no irrefutable evidence that one design is better than the other. The thought process is that the greater the separation there is between the wastegate gases and exhaust gases, the smoother the overall exhaust flow"

"Which downpipe has the best gains? There is no irrefutable evidence that any downpipe has better gains than another. The consensus, if there is one, is they are all within 5HP or less, gain wise, of each other."

^^^^^All quoted from the Dp Faq


Come back at me with some facts to prove your "speculation". I have also spoken with many tuners regarding "what style Dp should I buy?" and they have all said the same thing.........DONT always believe what is said on the internet regarding the infamous "bellmouth/divorced" Dp. Very little gains are seen between the 3 styles. But nasioc breeds "hype" so do what u want.

Last edited by shamrock 05; 11-21-2012 at 09:06 AM.
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Old 11-21-2012, 08:16 AM   #11
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FYI quoting the FAQ isn't always going to mean it's right.

That aside, OP pick any downpipe you want and can afford. Don't worry about a Wideband o2 bung if you don't even know what it does. Start slow.
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Old 11-21-2012, 09:04 AM   #12
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Originally Posted by HinshawWRX View Post
FYI quoting the FAQ isn't always going to mean it's right.

That aside, OP pick any downpipe you want and can afford. Don't worry about a Wideband o2 bung if you don't even know what it does. Start slow.
My point exactly, they are all the same.
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Old 11-21-2012, 12:22 PM   #13
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I got an eBay dp. Cheap and sounds good. 2 years and no welds have cracked and no figment problems that couldn't be fixed with pliers
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Old 11-21-2012, 08:06 PM   #14
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i always went with the catless ERZ its less than 200 and has both o2 sensor spots they give you caps if you dont need the one for the wideband
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Old 11-24-2012, 11:34 AM   #15
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Well I now have a AVO dp and a fujitsubo cbe on the car now, the hks flat flange and Cobb cbe is gone
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Old 11-24-2012, 12:19 PM   #16
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Originally Posted by shamrock 05 View Post
Well I now have a AVO dp and a fujitsubo cbe on the car now, the hks flat flange and Cobb cbe is gone
Wait, weren't you just arguing it didn't matter and then you went and bought a super expensive DP to replace the one that is "all the same"?

I do agree with the buy what you can afford philosophy, but you also gotta pay to play. Is an HKS DP better than stock? Yes. Will you get the same gains as with a bellmouth or divorced? Maybe. Simple CAD airflow maps I've seen, lead me to believe that the flow is much more consistent in either of those over the flat flange.
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Old 11-24-2012, 12:52 PM   #17
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Quote:
Originally Posted by subiedrivaa View Post
I want to buy an invidia bellmouth downpipe for my 03 WRX. Do i need to get one that has two o2 sensor bungs? or just one o2 sensor bung?
I have that same down pipe on my '02 wrx. It works great and has caused me no problems for the past few years. If that's the one you want, get it!
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Old 11-25-2012, 03:31 AM   #18
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Originally Posted by shamrock 05 View Post

Come back at me with some facts to prove your "speculation". I have also spoken with many tuners regarding "what style Dp should I buy?" and they have all said the same thing.........DONT always believe what is said on the internet regarding the infamous "bellmouth/divorced" Dp. Very little gains are seen between the 3 styles. But nasioc breeds "hype" so do what u want.
after many years of research and personal correspondence with people who have been playing with turbo Subaru's a LOT longer than just about anybody in north America
and after seeing more than a few dyno tunes....

I am 100% convinced that...and this is important....for stock location, iwg turbos, a divorced bellmouth design dp will yield the best results IF....IF the rest of the 'system' and the tune is done right.
The improvement is seen below 3500rpm(where most tuners ignore) and off the dyno as improved low load transient throttle response (which most dont take the time to tune well, if at all).

there is a great deal of power that virtually ALL subarus leave on the table because the exhaust is overlooked and/or just taken for granted by those who just dont know what they are doing...which is the very vast majority, here
just coating and/or wrapping the entire exhaust from the heads to the end of the dp is HUGE....and for more than one reason....but how many DO this???
meh.....not many

some of the biggest names in subarus....like Prodrive, have produced and used divorced wastegate dp's ......wonder why they went to the expense of designing and making and doing all that if it wasnt a good idea.....

anyway.....there are a LOT of automotive(and other) things that go against the common mans 'common sense' that really just go against the faulty, uneducated, 'logic' of the masses

im not so encumbered by faulty logic as i do and have done a great deal of research over the years....and i almost never post anything that isnt/hasnt been well researched......even if(when) it goes against what(almost) everybody else, here, thinks


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Old 11-25-2012, 03:36 AM   #19
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Quote:
Originally Posted by Uncle Scotty View Post
after many years of research and personal correspondence with people who have been playing with turbo Subaru's a LOT longer than just about anybody in north America
and after seeing more than a few dyno tunes....

I am 100% convinced that...and this is important....for stock location, iwg turbos, a divorced bellmouth design dp will yield the best results IF....IF the rest of the 'system' and the tune is done right.
The improvement is seen below 3500rpm(where most tuners ignore) and off the dyno as improved low load transient throttle response (which most dont take the time to tune well, if at all).

there is a great deal of power that virtually ALL subarus leave on the table because the exhaust is overlooked and/or just taken for granted by those who just dont know what they are doing...which is the very vast majority, here
just coating and/or wrapping the entire exhaust from the heads to the end of the dp is HUGE....and for more than one reason....but how many DO this???
meh.....not many

some of the biggest names in subarus....like Prodrive, have produced and used divorced wastegate dp's ......wonder why they went to the expense of designing and making and doing all that if it wasnt a good idea.....

anyway.....there are a LOT of automotive(and other) things that go against the common mans 'common sense' that really just go against the faulty, uneducated, 'logic' of the masses

im not so encumbered by faulty logic as i do and have done a great deal of research over the years....and i almost never post anything that isnt/hasnt been well researched......even if(when) it goes against what(almost) everybody else, here, thinks



You feeling ok d00d?
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Old 11-25-2012, 07:34 AM   #20
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You feeling ok d00d?
man.....i researched this back in 2002 and 2003...there was an aussie d000d that used to post here who had some really interesting results on his dyno.....he couldnt understand why some exhausts just made more power on his dyno......so he started actually LOOKING at what was what and came to some VERY interesting conclusions about exhaust design after fabbing up...making his own.... MANY different dp's and other exhaust parts
he even came up with volume of the pipe(in different places) and curve/bend angles(the upper and lower bends in the dp) that produced differences in where torque and hp was delivered....and it was mostly below 3500 rpm, and who doesnt want more power down low and better/faster throttle response???

and for stock location, iwg turbos, most of the 'common' ideas about exhausts are quite wrong unless just max WOT performance is all ya want...and for a dd street car, that isnt what is really important

i experimented a bit and liked the results......i know a couple other guys who really liked their results, too, after we swapped some parts and retuned

anyway.....dp design9and the rest of it too) really does make a difference...and what most think is the 'best' really isnt

i have a coated stromung shorty divorced dp on my car and now that i can afford it, im gonna do some other changes when i get all the parts together....and its ALL gonna be coated and/or wrapped from the heads all the way to the end of the midpipe, at least
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Old 03-04-2013, 02:16 PM   #21
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So, what downpipe(s) have the best build quality and fitment? Do any have heat shielding as part of their design? Or is wrapping the only option.

I'd like to buy one that needs no fiddling with fitment, hangers, brackets, etc. (i.e. fits as well as stock).

Thanks.
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Old 03-04-2013, 04:06 PM   #22
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Old 03-04-2013, 04:16 PM   #23
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Originally Posted by mmiller2002 View Post
So, what downpipe(s) have the best build quality and fitment? Do any have heat shielding as part of their design? Or is wrapping the only option.

I'd like to buy one that needs no fiddling with fitment, hangers, brackets, etc. (i.e. fits as well as stock).

Thanks.
I've tried many different downpipes and have never had an issue with any of them. Buy one that fits your budget and needs.
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Old 03-04-2013, 11:12 PM   #24
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Originally Posted by sevier2 View Post
I think this is what Uncle Scotty is talking about.

Subaru exhaust secrets The Dump pipe and splitter - YouTube

THAT is just PART of it.....the bend angles and the volumes of the pipes at different places also comrtibute to power delivery..as does keeping the heat IN the exhaust where it belongs.....
but...

kiddieo's just want what's cheap and k00 and dont wanna know no science and learnin and stuff like that cuz that's hard and ya gotta have lotsa learnin to unnastan all that junk and stuff
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Old 03-05-2013, 01:22 PM   #25
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That video makes me wonder if anyone has made a gasket/splitter to put in between the turbo and a bellmouth downpipe.
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