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Discussion Starter · #1 ·
Posted this on i-club with no response yet: I understand that the stock downpipe as well as several aftermarket downpipes have a flange that covers the turbo wastegate. Because this flange doesn't allow the gasses to flow easily, it could cause boost spikes, especially with a higher-flowing uppipe or downpipe. Some other downpipes (Bosal) have a separate pipe for the wastegate that empties into the downpipe further down the line while others have single-hole bellmouth design that flows both into the downpipe at the same opening. So, my question is, what would happen if I drilled a hole in the flange of whatever downpipe I decide to buy (HKS, Stromung, etc.)? Would that cause any problems (hot gasses being released into the engine compartment)? Would it have similar benefits to the other downpipe designs? Does anyone know?
 

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Discussion Starter · #4 ·
exhaust leak?

BamBool- I'm definitely no expert on this subject, but I thought that the wastegate only opens when the turbo is spinning and there is a sudden (or not-so-sudden) drop in engine rpm. The idea is to "waste" some of the compressed air from the turbo in order to keep the turbo from exploding from the extreme pressure of the compressed gas that has nowhere else to go. So, if the wastegate is only open when we're trying to LOSE boost pressure, what's the problem? There shouldn't be any problem holding boost when the wastegate is closed, right? That's what I would think, anyway. Is that incorrect? Thanks.
 

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If you drill a hole into the downpipe flange and you are at WOT you don't think all the exhaust is going down the pipe do you? Exhaust will leak out of that hole you drilled all the time... Not just when you let off of the gas.
 

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Discussion Starter · #6 ·
Take it easy big fella!

Hey sorry, I didn't mean any offense. I'm new to the inner workings of the turbocharged and intercooled, horizontally-opposed, internal combustion, four-cylinder engine. Please forgive me Mr. BamBool. Thanks for the info.
 

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Discussion Starter · #8 ·
Okay, I've never removed a downpipe before. So if the hole drilled in the flange would also release air from the exhaust system, then does that mean the wastegate and exhaust manifold are conjoined? I was under the impression that they were two different holes with some type of divider between them and that the downpipe gasket would prevent the exhaust gas from leaking through the flange hole. And if they're not divided, then why divide them with a design like the Bosal downpipe instead of a single bellmouth hole? Does anyone have a picture of the wastegate with the downpipe removed or can someone explain to me how it works? I feel really stupid but I'd like to know before I commit to anything.
 

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ok ok, lemme try to clear this up


if you look at the exhaust side of the turbo, there isn't a divider between the wastegate and the exhaust part, so if you drilled a hole in the dp over the part that covers the wastegate, alot of the exhaust gas will come out of there too - it'll just be like a huge ass exhaust leak, and you won't make any boost, plus you'll fry the engine compartment. also, one of the main reasons for the separate wastegate design is to allow gasses from the wastegate to bypass the catalytic converter so there is less backpressure, but (and i'm no expert, this is just my common sense acting here) if you have a catless exhaust, like the hks dp, then i doubt there will be that much of a problem w/ backpressure

-Robert
 

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OK, care to clear it up a little more for me? Seeing as the proposed hole is post-turbo, what is going to cause him not to make any boost? It may make the wastegate more efficient, in that for the given opening angle it is flowing more exhaust and spinning the turbine less...but that would just be less boost, not 0 boost.

thanks,

VV

Penguinking said:
ok ok, lemme try to clear this up


if you look at the exhaust side of the turbo, there isn't a divider between the wastegate and the exhaust part, so if you drilled a hole in the dp over the part that covers the wastegate, alot of the exhaust gas will come out of there too - it'll just be like a huge ass exhaust leak, and you won't make any boost, plus you'll fry the engine compartment. also, one of the main reasons for the separate wastegate design is to allow gasses from the wastegate to bypass the catalytic converter so there is less backpressure, but (and i'm no expert, this is just my common sense acting here) if you have a catless exhaust, like the hks dp, then i doubt there will be that much of a problem w/ backpressure

-Robert
 

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well technically it depends on the design - for example, the scoobysport exhaust has a bellmouth design, that is, the area around the turbo isn't cut off any, so if you drilled a hole in it, you'd basically be drilling a hole through the flange into the engine bay!!

i think this is best illustrated with pictures ;)
 

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and heres what another dp would look like


so you can see, drilling a hole for the wastegate on the first exhaust (above) would just make a hole in the dp
 

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Discussion Starter · #14 ·
BMP files WILL NOT work as attachments. Tim may look into this soon, but
assume that you should be using JPEG anyway from now on. Thanks.

-Jim
 

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I understand what it will look like/do. It won't cause the car not to boost, though. There are many cars with twin dump downpipes with the wastegate tube venting to atmosphere...essentially the same thing. That is what I'm getting at.

VV

Penguinking said:
and heres what another dp would look like


so you can see, drilling a hole for the wastegate on the first exhaust (above) would just make a hole in the dp
 

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Re: exhaust leak?

bone324 said:
BamBool- I'm definitely no expert on this subject, but I thought that the wastegate only opens when the turbo is spinning and there is a sudden (or not-so-sudden) drop in engine rpm. The idea is to "waste" some of the compressed air from the turbo in order to keep the turbo from exploding from the extreme pressure of the compressed gas that has nowhere else to go. So, if the wastegate is only open when we're trying to LOSE boost pressure, what's the problem? There shouldn't be any problem holding boost when the wastegate is closed, right? That's what I would think, anyway. Is that incorrect? Thanks.
I believe that you're talking about a bypass or Blow Off Valve (commonly referred to as a BOV) here. It's job is to release air trapped between the suddenly closed throttle plate and the compressor wheel of the turbocharger.

The wastegate is the mechanism that the turbocharger uses to vent excess pressure to regulate the amount of boost going into the motor. The boost controller (of whatever type commonly found on our favorite Scoobies) feeds pressure to the wastegate to control it's activation and that's what "regulates" the amount of boost fed to the engine.

I don't think that a hole drilled in the downpipe is a good idea (especially because my downpipe doesn't have any problems with spiking) but I can't see how it would cause a loss of boost.

FWIW my 4" TurboXS Bellmouth designed DP is one of the most beautiful pieces of metalwork I've put on a car and it made a HUGE seat of the pants difference in acceleration and throttle response.
 

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VetteVert said:
I understand what it will look like/do. It won't cause the car not to boost, though. There are many cars with twin dump downpipes with the wastegate tube venting to atmosphere...essentially the same thing. That is what I'm getting at.

VV

oh of course i understand what ur getting at - but with that kind of setup you'd have to completly separate out the gas comming from the wastegate - but w/ the stock...or really all the IHI turbos, you'd hafta put some kind of divider there before venting the wastegate to atmosphere.

...or you could always try to build some kind of external wastegate setup :D
 

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Discussion Starter · #18 ·
you'd hafta put some kind of
divider there before venting the wastegate to atmosphere
Yes, thank you, this whole thread started because I assumed that this divider already existed in the stock turbo. If there is no divider, then what keeps the wastegate and exhaust gasses from both entering the same hole in a twin dump design just as they would both leak through the hole in the wastegate flange? Really the wastegate dump seems like it would act more as a cat bypass for alot of the exhaust gas and a twin dump design shouldn't be much better than a bellmouth design(except that some of the exhaust gas is bypassing the cat and you get that cool sound everybody talks about).
 

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VetteVert said:
I understand what it will look like/do. It won't cause the car not to boost, though. There are many cars with twin dump downpipes with the wastegate tube venting to atmosphere...essentially the same thing. That is what I'm getting at.

VV

my thoughts exactly, how would the "hole drill" setup be any different than the divided w/g - d/p setup of some aftermarket d/ps?

dR
 

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I quit pressing the issue. Fact is, it won't be any different. While it would cause other problems, taking the downpipe off completely wouldn't cause the turbo to stop boosting. Maybe less (maybe more), but it definitely wouldn't stop boosting. I think he is confusing up and down pipes. A hole in the up-pipe would reduce boost, just not the downpipe.

VV

dark_rex said:


my thoughts exactly, how would the "hole drill" setup be any different than the divided w/g - d/p setup of some aftermarket d/ps?

dR
 
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