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Old 05-11-2004, 09:36 AM   #26
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The general theory is that an exhaust will not cause boost creep. It is the design of the VF-39 itself that causes this. Porting the wastegate should solve boost creep issues.
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Old 05-15-2004, 03:33 PM   #27
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I was wondering what is the stock downpipe's specs on a '04 WRX . So I do not replace a stock pipe with a pipe that is not anybetter.
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Old 05-15-2004, 03:38 PM   #28
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Quote:
Originally posted by STUDAndring
I was wondering what is the stock downpipe's specs on a '04 WRX . So I do not replace a stock pipe with a pipe that is not anybetter.
They're the same as an 02-03 downpipe as far as I can tell. All of the above info applies to the 04 models.
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Old 07-20-2004, 07:06 PM   #29
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I'm having a hard time understand how/why the stock downpipe covers the waste gate section, while the other designs all merge the waste gate exaust into the pipe somewhere? So does the stock turbo dump anything into the waste gate at all? If so, why is the stock DP waste gate section covered?
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Old 07-20-2004, 07:09 PM   #30
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With the stocker, the gasses from the wastegate slam right into the flat part of the DP flange, where it meets up with the turbo. Then the gasses have to make a 90 degree turn, right into the main portion of the DP. This causes turbulence.
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Old 08-29-2004, 09:44 PM   #31
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WOW...THANKS for all the info. Just bought an HKS DP and was searching for some more info. You wrapped it up and then some!!!
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Old 08-30-2004, 09:52 AM   #32
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Quote:
Originally Posted by Unabomber
The general theory is that an exhaust will not cause boost creep. It is the design of the VF-39 itself that causes this. Porting the wastegate should solve boost creep issues.
Boost creep is a caused by the wastegate not allowing enough exhaust gasses to pass thru it. When you increase the flow of the exhaust by changing it, you run into the problem of the stock wastegate not being able to by-pass the extra flow. Thus you get boost creep. It's a purely mechanical/flow problem. It doesn't have anything to do with boost controllers, etc.

Porting, or increasing the size of, the wastegate will allow more exhaust to pass thru the gate. This will solve the creap problems.
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Old 08-31-2004, 05:04 PM   #33
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Is it true that divorced downpipes also prevent boost creep?
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Old 08-31-2004, 05:06 PM   #34
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Nope.
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Old 08-31-2004, 05:30 PM   #35
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Thanks, and I like your title
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Old 09-14-2004, 06:01 PM   #36
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what horsepower gains are u lookin at between a short dp and a dp that eliminates the third cat? assuming only mod is a catback at the moment.
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Old 09-14-2004, 09:54 PM   #37
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No one really knows. Best guesstimate I have heard is 5HP per cat, so no cat + longer/bigger pipe = 7HP on my GuessDynoŽ vs. a short catless downpipe.
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Old 10-07-2004, 11:03 PM   #38
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bumping for the non-searching types.
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Old 10-12-2004, 07:29 PM   #39
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Quote:
Originally Posted by billzebub
bumping for the non-searching types.
bump
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Old 10-25-2004, 02:34 AM   #40
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Question Wastegate porting

"Porting, or increasing the size of, the wastegate will allow more exhaust to pass thru the gate. This will solve the creap problems."

Does anyone know what the stock diameter is and to what dimensions the gate should be ported to? Can this be done with the exhaust pieces removed and leaving the turbo attached to the car? My assumption is I should probably remove the turbo but it would save time if I didn't have to. Are there any gotchas to doing this myself using a Dremel or drill? Or should I have a machine shop do it using a heavy drill press?

Thanks
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Old 10-25-2004, 07:22 AM   #41
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You will have to search for your answer please as this thread is about downpipes. Search hard as wastegate porting is both a science and an art and isn't as simple as boring out a hole.
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Old 11-19-2004, 05:50 AM   #42
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Question

Quote:
Originally Posted by snvin
With the stocker, the gasses from the wastegate slam right into the flat part of the DP flange, where it meets up with the turbo. Then the gasses have to make a 90 degree turn, right into the main portion of the DP. This causes turbulence.
So is that turbulence cause by the gasses from the wastegate the important part? or is the seperation of the exhaust gas and the waste gas important?

If so, then wouldn't stock be better than the bellmouth, while the divorced be more efficient than stock?

This concern of mine postpone my decision on helix downpipe.
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Old 11-19-2004, 11:12 AM   #43
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Quote:
Originally Posted by hey1
So is that turbulence cause by the gasses from the wastegate the important part? or is the seperation of the exhaust gas and the waste gas important?

If so, then wouldn't stock be better than the bellmouth, while the divorced be more efficient than stock?

This concern of mine postpone my decision on helix downpipe.
You are thinking too much about this. The stock design is crap, and the bellmouth = divorced performance. The turbulence is the bad part, not the seperation of gases.
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Old 11-19-2004, 04:51 PM   #44
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Quote:
Originally Posted by mbiker97
You are thinking too much about this. The stock design is crap, and the bellmouth = divorced performance. The turbulence is the bad part, not the seperation of gases.
Well.. I don't want to sound all gullable, but according to the original post of this FAQ, "The thought process is that the greater the separation there is between the wastegate gases and exhaust gases, the smoother the overall exhaust flow."

So in some way, one should be more efficient than another downpipe. If the turbulance really is that bad part, then perhaps the divorced flange is better because there must be an important reason why they have a design to separate the two distinct gasses to begin with. So is there anyone that has experiences with both bell mouth and divorced downpipe before?
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Old 11-19-2004, 06:56 PM   #45
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Search, this isn't a new topic

Drew
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Old 11-19-2004, 07:11 PM   #46
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Quote:
Originally Posted by hey1

So in some way, one should be more efficient than another downpipe. If the turbulance really is that bad part, then perhaps the divorced flange is better because there must be an important reason why they have a design to separate the two distinct gasses to begin with. So is there anyone that has experiences with both bell mouth and divorced downpipe before?

Different tuners have different theories regarding this.
Some say divorced is better, some prefer bellmouth. Both are good.
Personally, I have a divorced DP (Bosal), and I have experienced no issues with it whatsoever -- but I am running the divorced design because I wanted a 'short' DP that would allow me to use the stock 3rd cat, and most 'short' DPs are divorced/twin dump.
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Old 11-19-2004, 11:03 PM   #47
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Quote:
Originally Posted by WRX8XB
Search, this isn't a new topic

Drew
I did, else I would've started a new thread.
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Old 11-20-2004, 05:26 AM   #48
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Does having a DP cause flames or just removing the cats?
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Old 11-20-2004, 08:28 AM   #49
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No cats causes flames, but 99% of the time you will be flame free unless you have a bad tune or a 100% atmospheric BOV.
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Old 11-21-2004, 03:47 AM   #50
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Does anyone or any tuner have proof of a divorced/twin dump being better then a bellmouth or the other way around?

Im looking to get the RSR DP...to mate to the RSR catback.
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