why did it do that? -boost creep-
03-24-2004 | 05:29 PM
#46
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Posts: n/a
boost creep?
im gonna ask my sevice manager about this topic.he drives a sti and it has a turbo back after market exhaust on it .i dont know if he has a cat or has had his waste gate ported but i will call tomorrow to see what input he has to offer. silverfox1
03-31-2004 | 12:29 AM
#49
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Posts: n/a
Add to sticky on Boost Creep
I will attempt to answer some unanswered questions in addition to the sticky->
Copied from wgknestick's STICKY on NASIOC:
"With the countless threads about boost creep problems with turbobacks on the 2.5l STI, I think this thread should be helpful as a quick summary to those planning on moddifying their STI.
Q) What is boost creep?
A) Boost creep occurs when the wastegate is physically unable to bypass enough exhaust around the turbine on the turbo.
Q) Is boost creep harmful?
A) Yes, boost creep is one of the worst problems you can have with a turbo engine. Boost creep means that there is NO way for the boost pressure to be controlled. Boost pressures in excess of 20psi!!! have been recorded on STIs with TBE before the ECU cuts fuel.
Q) What causes boost creep?
A) Installing a turbo back exhaust whether aftermarket catted or not will in almost all cases cause boost creep to a certain extent.
Q) How do I know if I have boost creep?
A) If you have a full TBE, then you probably have it. A boost gauge will tell you what pressure you are at as well. Fuel cut occurs when the ECU senses boost in excess of 17.5psi for 2-3s. Fuel cut in my experience is a very violent "stutter" from the engine that resembles extreme knock, followed by CEL.
Q) What is the overboost CEL?
A) (P0244) Wastegate malfunction
Q) Is there anything else I can do besides porting the wastegate to prevent the creeping....MBC, EBC, engine management etc?
A) This problem is isolated to the wastegate only. The wastegate is a mechanical system. There are no current workarounds or "fixes" besides this. The 2.5l just flows too much exhaust through the turbo once a turbo back has been added for the wastegate to control boost. If you think of it as a hierarchy, then it should make sense."
I copied the parts of the sticky which I agree with.
continued....
merged with 'sticky' thread on boost creep.
Copied from wgknestick's STICKY on NASIOC:
"With the countless threads about boost creep problems with turbobacks on the 2.5l STI, I think this thread should be helpful as a quick summary to those planning on moddifying their STI.
Q) What is boost creep?
A) Boost creep occurs when the wastegate is physically unable to bypass enough exhaust around the turbine on the turbo.
Q) Is boost creep harmful?
A) Yes, boost creep is one of the worst problems you can have with a turbo engine. Boost creep means that there is NO way for the boost pressure to be controlled. Boost pressures in excess of 20psi!!! have been recorded on STIs with TBE before the ECU cuts fuel.
Q) What causes boost creep?
A) Installing a turbo back exhaust whether aftermarket catted or not will in almost all cases cause boost creep to a certain extent.
Q) How do I know if I have boost creep?
A) If you have a full TBE, then you probably have it. A boost gauge will tell you what pressure you are at as well. Fuel cut occurs when the ECU senses boost in excess of 17.5psi for 2-3s. Fuel cut in my experience is a very violent "stutter" from the engine that resembles extreme knock, followed by CEL.
Q) What is the overboost CEL?
A) (P0244) Wastegate malfunction
Q) Is there anything else I can do besides porting the wastegate to prevent the creeping....MBC, EBC, engine management etc?
A) This problem is isolated to the wastegate only. The wastegate is a mechanical system. There are no current workarounds or "fixes" besides this. The 2.5l just flows too much exhaust through the turbo once a turbo back has been added for the wastegate to control boost. If you think of it as a hierarchy, then it should make sense."
I copied the parts of the sticky which I agree with.
continued....
merged with 'sticky' thread on boost creep.
Last edited by Wingless Wonder; 04-21-2004 at 02:07 PM.
03-31-2004 | 12:30 AM
#50
Guest
Posts: n/a
Now boost creep is a physical property of the wastegate not being large enough as stated above. When experiencing boost creep, the air follows the path of least resistance and it flows out of the turbine which spins the turbo even faster.
The EASIEST AND ONLY way to solve this is with a properly ported wastegate ONLY.
I want a TBE/downpipe that does not cause boost creep!
- A properly designed turboback/downpipe that does what is supposed to do (essentially give you the least amount of backpressure so air can flow rapidly out of the exhaust) will give you the most amount of boost creep. If you get crazy amounts of boost creep, you have a very well made exhaust IMO.
-In regards to downpipe design causing air turbulence which in turn causes boost creep: I believe that all downpipes on the market have been tried and tested and are all well designed. I do not believe that the answer to stopping boost creep is only in downpipe design!! It may play a small part, but not enough to prevent boost creep.
How come some people get boost creep and others do not?
- Well one thing to take into consideration. Some people interchange the terms boost creep and fuel cut. They are not the same thing so be careful in what you read. Some skepticism is necessary when reading other people's posts.
There are many many variables that influence the amount of boost creep you will get. Some of these are
(1) slight differences in the casting of the exhaust side of the turbo from car to car, (2) air temperature-colder air will give you more creep, (3) elevation-closer to sea level will give you more creep, (4) humidity-less humidity will give you more creep, (5) the restrictiveness of your exhaust system - the less restrictive, the more creep you will experience (6) The change in exhaust temp. though the turbine-> the downpipe (if the exhaust temp. drops drastically after exiting the turbo this will reduce the volume of the air and allow it to exit the exhaust faster due to the drop in pressure but for vf39's it will cause more creep), (7) driving style-people who drive "harder" than others will obviously experience boost creep more often...
I'm sure I may have missed some others...
-My whole point is, do not run off and buy X downpipe or TBE ONLY because some guy in X part of the country does not get boost creep (or i should say fuel cut). There are too many variables to account for. Expect to get creep.
-CATBACK or AXELBACK = No creep
-TBE, CATTED or NOT CATTED = Boost creep
-DOWNPIPE = a grey area. Depending on environmental conditions and how free flowing it is, you may or may not get boost creep.
-Remember these are generalizations. It depends on the conditions of where you live and other factors listed above.
Well I want a different exhaust - What do I do?
-Well it depends on what you're looking for. If you want a more aggressive sound, just get a catback or axelback. Boost creep issues have not been reported with them.
If you want to gain some horsepower and torque you have some options to combat creep.
(1) Get an external wastegate- This is quite a bit of work. You will have to get custom piping and weld the wastegate onto it. Also the internal wastegate must be welded shut.
(2) Get another turbo- with proper supporting mods of course (fuel management, engine management)
(3) Port the wastegate ONLY- Best and easiest way to cure this.
Okay how do I go about porting the wastegate?
-DO A SEARCH!!
j/k! Well you will have to search on how to remove your turbo. After that is done take a grinding tool of your choice. I use a carbide bit on air tools. You can use a dremel with a grinding stone as well but this will take much longer.
The main thing you do NOT want to do is OVERPORT the hole. You should take ~70% of the material out leaving enough of a lip to have the flapper SEAL properly. Also note that there is some play with the flapper, so occasionally wiggle it around to make sure you do not overport. If you do overport, you will get lower than stock boost levels at WOT! Another tip is to angle the grinding tool and remove material beneath the wastegate at an angle. This will make it wider beneath the flapper enabling more air to flow though.
The EASIEST AND ONLY way to solve this is with a properly ported wastegate ONLY.
I want a TBE/downpipe that does not cause boost creep!
- A properly designed turboback/downpipe that does what is supposed to do (essentially give you the least amount of backpressure so air can flow rapidly out of the exhaust) will give you the most amount of boost creep. If you get crazy amounts of boost creep, you have a very well made exhaust IMO.
-In regards to downpipe design causing air turbulence which in turn causes boost creep: I believe that all downpipes on the market have been tried and tested and are all well designed. I do not believe that the answer to stopping boost creep is only in downpipe design!! It may play a small part, but not enough to prevent boost creep.
How come some people get boost creep and others do not?
- Well one thing to take into consideration. Some people interchange the terms boost creep and fuel cut. They are not the same thing so be careful in what you read. Some skepticism is necessary when reading other people's posts.
There are many many variables that influence the amount of boost creep you will get. Some of these are
(1) slight differences in the casting of the exhaust side of the turbo from car to car, (2) air temperature-colder air will give you more creep, (3) elevation-closer to sea level will give you more creep, (4) humidity-less humidity will give you more creep, (5) the restrictiveness of your exhaust system - the less restrictive, the more creep you will experience (6) The change in exhaust temp. though the turbine-> the downpipe (if the exhaust temp. drops drastically after exiting the turbo this will reduce the volume of the air and allow it to exit the exhaust faster due to the drop in pressure but for vf39's it will cause more creep), (7) driving style-people who drive "harder" than others will obviously experience boost creep more often...
I'm sure I may have missed some others...
-My whole point is, do not run off and buy X downpipe or TBE ONLY because some guy in X part of the country does not get boost creep (or i should say fuel cut). There are too many variables to account for. Expect to get creep.
-CATBACK or AXELBACK = No creep
-TBE, CATTED or NOT CATTED = Boost creep
-DOWNPIPE = a grey area. Depending on environmental conditions and how free flowing it is, you may or may not get boost creep.
-Remember these are generalizations. It depends on the conditions of where you live and other factors listed above.
Well I want a different exhaust - What do I do?
-Well it depends on what you're looking for. If you want a more aggressive sound, just get a catback or axelback. Boost creep issues have not been reported with them.
If you want to gain some horsepower and torque you have some options to combat creep.
(1) Get an external wastegate- This is quite a bit of work. You will have to get custom piping and weld the wastegate onto it. Also the internal wastegate must be welded shut.
(2) Get another turbo- with proper supporting mods of course (fuel management, engine management)
(3) Port the wastegate ONLY- Best and easiest way to cure this.
Okay how do I go about porting the wastegate?
-DO A SEARCH!!
j/k! Well you will have to search on how to remove your turbo. After that is done take a grinding tool of your choice. I use a carbide bit on air tools. You can use a dremel with a grinding stone as well but this will take much longer.The main thing you do NOT want to do is OVERPORT the hole. You should take ~70% of the material out leaving enough of a lip to have the flapper SEAL properly. Also note that there is some play with the flapper, so occasionally wiggle it around to make sure you do not overport. If you do overport, you will get lower than stock boost levels at WOT! Another tip is to angle the grinding tool and remove material beneath the wastegate at an angle. This will make it wider beneath the flapper enabling more air to flow though.
Last edited by blueballs; 04-05-2004 at 06:34 PM.
03-31-2004 | 12:33 AM
#51
Guest
Posts: n/a
Current problems:
A port and polish of the whole exhaust side may result in boost creep! WHY??
- Because you are essentially increasing the airflow thought the turbine w/ a port and polish, which we do not want in our case. If boost creep is caused by air following the path of least resistance (the turbine) and you increase the amount of air that can flow though the turbine with a PnP, you will get boost creep.
-Do not get a complete exhaust Port and Polish. Only do the wastegate!!
Well my wastegate was ported as well and I still get creep!
- Well this goes to show you that an excellent job was done in porting the exhaust side. Unfortunately for our VF39s ONLY, our wastegate design is not as efficient as other turbos (ie other IHI turbo's and TD04s). You will still experience creep. One solution to this is porting the hole to a size larger than the stock flapper can seal to divert even more air out of the wastegate to prevent creep. The problem is finding a company that can make an oversized flapper for us so the wastegate can be ported to a large diameter that does not cause creep.
Who does this guy think he is? How does he know this stuff for sure?
Well, I do alot of reaserch online. This along with the experience of my friends I have come to the above conclusions. Me and my freind (an STi mechanic) have ported my own wastegate and a couple of other local STi's with 100% success rate! I have even tested it out on the coldest day in Central NY. -10 degrees going WOT in all gears 1st-6th. Boost remained at .1mpa
People I have done it for have reported no problems.
I am not impressed, where are the technical graphs, flow charts, wastegate actuator maps?
I believe there is something called Paralysis by Overanalysis. For this case, a wastegate port is not a big deal. I think everyone should get used to the fact that you will more than likely have to port your wastegate with exhaust mods on a stock turbo. There is no way around it. (remember the variables: for example if you live 1000ft above sea level and it is between 65-95 degrees year round and humid you may not get creep, but who knows - every case is different).
Well a boost controller or some other electronic gizmo or Ebay item worked for me!
- Well I'm glad. This will not work for everyone though. A boost controller may help SLIGHTLY with someone who does not have much boost creep. It may increase the response of the wastegate and have it open sooner but even with the wastegate fully open, the boost will still creep to possibly unsafe levels especially in the higher gears. A boost controller combined with a ported wastegate is probably the best combination you can have to completely cure boost creep.
Any questions/additions/suggestions - post em up! or PM me
Hope this was useful
Ro
A port and polish of the whole exhaust side may result in boost creep! WHY??
- Because you are essentially increasing the airflow thought the turbine w/ a port and polish, which we do not want in our case. If boost creep is caused by air following the path of least resistance (the turbine) and you increase the amount of air that can flow though the turbine with a PnP, you will get boost creep.
-Do not get a complete exhaust Port and Polish. Only do the wastegate!!
Well my wastegate was ported as well and I still get creep!
- Well this goes to show you that an excellent job was done in porting the exhaust side. Unfortunately for our VF39s ONLY, our wastegate design is not as efficient as other turbos (ie other IHI turbo's and TD04s). You will still experience creep. One solution to this is porting the hole to a size larger than the stock flapper can seal to divert even more air out of the wastegate to prevent creep. The problem is finding a company that can make an oversized flapper for us so the wastegate can be ported to a large diameter that does not cause creep.
Who does this guy think he is? How does he know this stuff for sure?
Well, I do alot of reaserch online. This along with the experience of my friends I have come to the above conclusions. Me and my freind (an STi mechanic) have ported my own wastegate and a couple of other local STi's with 100% success rate! I have even tested it out on the coldest day in Central NY. -10 degrees going WOT in all gears 1st-6th. Boost remained at .1mpa
People I have done it for have reported no problems.
I am not impressed, where are the technical graphs, flow charts, wastegate actuator maps?
I believe there is something called Paralysis by Overanalysis. For this case, a wastegate port is not a big deal. I think everyone should get used to the fact that you will more than likely have to port your wastegate with exhaust mods on a stock turbo. There is no way around it. (remember the variables: for example if you live 1000ft above sea level and it is between 65-95 degrees year round and humid you may not get creep, but who knows - every case is different).
Well a boost controller or some other electronic gizmo or Ebay item worked for me!
- Well I'm glad. This will not work for everyone though. A boost controller may help SLIGHTLY with someone who does not have much boost creep. It may increase the response of the wastegate and have it open sooner but even with the wastegate fully open, the boost will still creep to possibly unsafe levels especially in the higher gears. A boost controller combined with a ported wastegate is probably the best combination you can have to completely cure boost creep.
Any questions/additions/suggestions - post em up! or PM me
Hope this was useful
Ro
04-17-2004 | 06:25 PM
#56
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Posts: n/a
boost creep?
the parts manager at masto suburu has sold 5 APS tbe's to sti owners and has not heard from any of them concerning boost creep. two of them were sold with high flow cats included and three were catless.he said the sevice manager is runing after market tbe and has not had any boost creep issues. he hasnt had his waste gate ported either.he couldnt remember the brand of his exhaust though.it was sevice managers day off.siverfox1
04-19-2004 | 09:49 AM
#57
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Registered User
Joined: Oct 2003
Posts: 436
From: cali
Car Info: sti wrb
Re: boost creep?
Originally posted by silverfox1
the parts manager at masto suburu has sold 5 APS tbe's to sti owners and has not heard from any of them concerning boost creep. two of them were sold with high flow cats included and three were catless.he said the sevice manager is runing after market tbe and has not had any boost creep issues. he hasnt had his waste gate ported either.he couldnt remember the brand of his exhaust though.it was sevice managers day off.siverfox1
the parts manager at masto suburu has sold 5 APS tbe's to sti owners and has not heard from any of them concerning boost creep. two of them were sold with high flow cats included and three were catless.he said the sevice manager is runing after market tbe and has not had any boost creep issues. he hasnt had his waste gate ported either.he couldnt remember the brand of his exhaust though.it was sevice managers day off.siverfox1
04-20-2004 | 06:02 PM
#58
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Posts: n/a
boost creep
serice manager at mastro subaru in tampa runs his sti at the track on race gas of 107 octane so i guess you would say he does run it hard and hasnt had boost creep while gaining 20 hp at the wheels with tbe that was dynoed at dealership at 266 stock and 286 after replacing stock system with aps tbe.silverfox1
04-22-2004 | 04:33 PM
#59
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Posts: n/a
First off, thanks for all the info Blueballs, but my question is what if i were to get the wastegate side ported and the exhaust side ported also? will it still creep? will there be any performance gains? pros/cons? spool up faster perhaps? or maybe it will just bring back the dreaded creep ?!