STi7 UK boost spikes solution suggestion
27 November 2002, 12:52 PM
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As far as I know the problem with boost spikes on STI7 UK has not been solved yet. The problem seems to be in the wastegate being too restrictive. The only solution here is changing the turbo to the one with bigger wastegate.
Here's my idea on solving this problem and sticking to the stock turbo. This is just and idea and may cost the same as buying new turbo, so don't be too hard on me
What if you install an external wastegate on the uppipe before the turbo and somehow disengage the stock actuator. The ext. wastegate can purge all teh exhaust gasses to atmosphere aswell. Who do you guys think of this idea?
Nick
Here's my idea on solving this problem and sticking to the stock turbo. This is just and idea and may cost the same as buying new turbo, so don't be too hard on me
What if you install an external wastegate on the uppipe before the turbo and somehow disengage the stock actuator. The ext. wastegate can purge all teh exhaust gasses to atmosphere aswell. Who do you guys think of this idea?
Nick
27 November 2002, 01:31 PM
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Nick
You would never get spikes, because the turbine would probably always be spinning too slowly!
You would have the turbine stall when the wastegate in the up pipe opened, and this would provide wildly fluctuating pressure from the compressor.
The wastegate needs to be on the outlet side of the turbine, not the inlet
You would never get spikes, because the turbine would probably always be spinning too slowly!
You would have the turbine stall when the wastegate in the up pipe opened, and this would provide wildly fluctuating pressure from the compressor.
The wastegate needs to be on the outlet side of the turbine, not the inlet
27 November 2002, 01:38 PM
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Dave,
Ofcourse there's no spikes with PPP
That how the external wastegates are usually installed - before the turbo inlet and the purge after the turbo outlet. The exhaust gasses are supposed to bypass the turbo. What's the point of installing after the turbo outlet?
Ofcourse there's no spikes with PPP
That how the external wastegates are usually installed - before the turbo inlet and the purge after the turbo outlet. The exhaust gasses are supposed to bypass the turbo. What's the point of installing after the turbo outlet?
27 November 2002, 07:00 PM
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The spikes are easily resolved by increasing the diameter of the restrictor in the wastegate actuator line.
Best option is to put in an adjustable flow control valve as it lets you fine tune the boost response.
Best option is to put in an adjustable flow control valve as it lets you fine tune the boost response.
27 November 2002, 09:02 PM
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I'm not sure about that. I've tried installing a boost controller (removing all the restrictors) and it wouldn't help even if you turn it off. Basicly when you turn off the BC the wastegate only holds the boost to the preset actuator spring strength. You can still see the boost spikes up to 1.2bar above 5500-6000rpm.
Just to clarify: I'm talking about boost spike that you get after installing an exhaust.
Just to clarify: I'm talking about boost spike that you get after installing an exhaust.
28 November 2002, 09:30 AM
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Before the usual crew start I'm not trying to sell anything, rather commenting on something I have experience of, ok? 
When I decatted my STI Type UK I was experiencing boost spikes of 1.6 bar, I regulate this with a Dawes device down to 1.2 bar held in 5th, 1 bar in 6th. I monitor everything using delta dash, so my AFR suggests that I could probably push the boost slightly higher, but I would rather aire on the side of caution for now. The car even feels much quicker for it. I have fitted the dawes to quite a few cars for the same purpose.
Also have any of you noticed any turbulance when on boost? The other reason my boost is relatively low is that I was getting a fluttering sound which suggests to me that the open neck downpipe I'm running at the moment is causeing a lot of turbulance when the exhaust gasses mix from the wastegate and turbo collector? My new siamese design will be on shortly so should hopefully rectify this.
Jamie
www.j-w-racing.com
When I decatted my STI Type UK I was experiencing boost spikes of 1.6 bar, I regulate this with a Dawes device down to 1.2 bar held in 5th, 1 bar in 6th. I monitor everything using delta dash, so my AFR suggests that I could probably push the boost slightly higher, but I would rather aire on the side of caution for now. The car even feels much quicker for it. I have fitted the dawes to quite a few cars for the same purpose.
Also have any of you noticed any turbulance when on boost? The other reason my boost is relatively low is that I was getting a fluttering sound which suggests to me that the open neck downpipe I'm running at the moment is causeing a lot of turbulance when the exhaust gasses mix from the wastegate and turbo collector? My new siamese design will be on shortly so should hopefully rectify this.
Jamie
www.j-w-racing.com
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28 November 2002, 09:58 AM
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The boost spikes on the STI 7 are due to the way boost is controlled by the Type UK ECU. When the exhaust is changed (and the ECU is not) it can no longer keep the boost under control - the boost pressure rises quicker than the ECU drops the wastegate duty.
There are actually two versions of STI 7 Type UK ECU. One will exhibit this problem far more severely than the other.
It would be really interesting if you guys could check your ECU versions - it's written on the lid of the ECU, below the passenger kick plate. Both versions are ag820, but the minor version is different. The 090 version should be the one that misbehaves, whereas the 2591 version should behave better. This can of course be fixed ;-)
The Prodrive ECU version alters the wastegate duty to account for the free flowing exhaust they add, hence no overboost.
Like you say, they hold 15 PSI of boost at the redline with zero wastegate duty, but that's a different problem. As you say, wastegate too small.
Cheers
Steve
There are actually two versions of STI 7 Type UK ECU. One will exhibit this problem far more severely than the other.
It would be really interesting if you guys could check your ECU versions - it's written on the lid of the ECU, below the passenger kick plate. Both versions are ag820, but the minor version is different. The 090 version should be the one that misbehaves, whereas the 2591 version should behave better. This can of course be fixed ;-)
The Prodrive ECU version alters the wastegate duty to account for the free flowing exhaust they add, hence no overboost.
Like you say, they hold 15 PSI of boost at the redline with zero wastegate duty, but that's a different problem. As you say, wastegate too small.
Cheers
Steve
28 November 2002, 10:08 AM
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Once again. In my case the ECU does not controll boost any more since the controlling solenoid has been disconnected. The boost controlled (Blitz SBC i-D) cannot cope with the spikes even when it is turned off or the boost and gain settings are set to zero. The only solution I found was inserting a silencer that comes with most of the japanese backboxes, to create more backpressure. I remember someone here said that he tried connecting the solenoid to turbine outlet so the wastegate stays open. He said that he has seen the boost rise way above zero at WOT.
28 November 2002, 10:33 AM
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It's interesting that it's far worse on japanese STIs than the Type UK when decatted. Do you know of any other differences between the cars that could cause this.
There must be a boost pressure / air flow above which there is no return, if you see what I mean. If you stay below this, then the wastegate can still cope. Perhaps try taking the target boost down very slightly to tip the scales back the other way.
Cheers
Steve
There must be a boost pressure / air flow above which there is no return, if you see what I mean. If you stay below this, then the wastegate can still cope. Perhaps try taking the target boost down very slightly to tip the scales back the other way.
Cheers
Steve
28 November 2002, 10:40 AM
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I actually tried it on both UK STI and the japanese one. Both cars have been fully decatted + exhaust manifold, both had EBCs installed. The results: the japanese STI has no problem holding the boost, the UK STI gets spikes up to 1.3-1.4 bar. As far as I know the above cars have different turbos. UK STI - IHI VF35, JDM STI - IHI VF30.
28 November 2002, 10:49 AM
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quote from D T-S
Err, I think you've got that wrong Dave.
If you put the wastegate after the turbine you'd have no control of the amount of gas going through the turbine, hence no control over boost. As Nick stated, you would need to put the wastegate prior to the turbine to get control. If you look at a standard turbo, the wastegate penny lets gases straight past the turbine into the downpipe.
The use of an external wastegate on a VF30 has been tried by one of our "cousins" - see the posts from "Alfriedesq" on nasioc.com (the old i-Club) about his experiences.
The idea of dumping the gases vented from the wastegate direct to atmosphere is a good one, although it would be technically illegal over here in the UK.
Duncan
The wastegate needs to be on the outlet side of the turbine, not the inlet
If you put the wastegate after the turbine you'd have no control of the amount of gas going through the turbine, hence no control over boost. As Nick stated, you would need to put the wastegate prior to the turbine to get control. If you look at a standard turbo, the wastegate penny lets gases straight past the turbine into the downpipe.
The use of an external wastegate on a VF30 has been tried by one of our "cousins" - see the posts from "Alfriedesq" on nasioc.com (the old i-Club) about his experiences.
The idea of dumping the gases vented from the wastegate direct to atmosphere is a good one, although it would be technically illegal over here in the UK.
Duncan
28 November 2002, 02:02 PM
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Duncan
Doh! - sorry, brain out - I conjured up a quick mental picture of a turbo in my mind before posting, but of course the bit on the downpipe side of the turbo is the wastegate outlet, not the inlet......
Doh! - sorry, brain out - I conjured up a quick mental picture of a turbo in my mind before posting, but of course the bit on the downpipe side of the turbo is the wastegate outlet, not the inlet......
28 November 2002, 06:48 PM
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Hi Gevor (Nick)
Welcome to the STi7 "boost creep" club. I believe there are 3 of us now including yourself!!!What you are talking about is "boost creep" (5000/5500rpm and up gradual boost rise to 1.3/1.4 bar) not the boost spikes (3000 to 4000rpm rapid boost rise to 1.5/1.7 bar when the car first comes on boost) which are commonly solved using either larger restrictors, bleed valves or Electronic Boost Controllers.
I solved my problem by putting the standard exhaust back on!!!!!This is torture after feeling the car without those restrictive cats and back box.
I believe the wastegate diameter is not the problem, but the poor design of the wastegate channel means that some rough castings (The 3 of us with boost creep)of the turbo are perhaps causing turbulence of the exhaust gases before the exit of the wastegate inside the turbo. The way to solve this is to port the wastegate smoother for better flow. I do not feel like messing with the turbo though. We are getting a catless exhaust with our PPP for the STi 7 in South Africa soon (Been waiting 6 months!!!) so I am confident Subaru South Africa will have to solve the problem for me Hehehe!!! It will be interesting to see how they propose to solve the problem. New Turbo here I come!!!! An external wastegate is another solution, but then you need a different turbo anyway.
The frustrated "Boost Creeper"
Welcome to the STi7 "boost creep" club. I believe there are 3 of us now including yourself!!!What you are talking about is "boost creep" (5000/5500rpm and up gradual boost rise to 1.3/1.4 bar) not the boost spikes (3000 to 4000rpm rapid boost rise to 1.5/1.7 bar when the car first comes on boost) which are commonly solved using either larger restrictors, bleed valves or Electronic Boost Controllers.
I solved my problem by putting the standard exhaust back on!!!!!This is torture after feeling the car without those restrictive cats and back box.
I believe the wastegate diameter is not the problem, but the poor design of the wastegate channel means that some rough castings (The 3 of us with boost creep)of the turbo are perhaps causing turbulence of the exhaust gases before the exit of the wastegate inside the turbo. The way to solve this is to port the wastegate smoother for better flow. I do not feel like messing with the turbo though. We are getting a catless exhaust with our PPP for the STi 7 in South Africa soon (Been waiting 6 months!!!) so I am confident Subaru South Africa will have to solve the problem for me Hehehe!!! It will be interesting to see how they propose to solve the problem. New Turbo here I come!!!! An external wastegate is another solution, but then you need a different turbo anyway.
The frustrated "Boost Creeper"
29 November 2002, 09:21 AM
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Matt
My MY01 WRX has a TD04, and I think that you'll find that the early New Age STi had a VF30 (including the UK spec cars), the Type C started the VF34s but that the later Jap Spec cars now have them as well, and that some Aus spec cars have VF35s. However, the Jap Spec cars should now be moving on to the twin outlet turbos ....
Confused? I am!
Duncan
My MY01 WRX has a TD04, and I think that you'll find that the early New Age STi had a VF30 (including the UK spec cars), the Type C started the VF34s but that the later Jap Spec cars now have them as well, and that some Aus spec cars have VF35s. However, the Jap Spec cars should now be moving on to the twin outlet turbos ....
Confused? I am!
Duncan
29 November 2002, 09:30 AM
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Strange that one, Ive had my turbo off twice (just for a laugh ) and stamped on the compressor housing was VF30, have I been short-changed?
It will be coming off for good in January so hopefully I wont have to do it again!
Jamie
www.j-w-racing.com
) and stamped on the compressor housing was VF30, have I been short-changed? It will be coming off for good in January so hopefully I wont have to do it again!
Jamie
www.j-w-racing.com
03 December 2002, 12:42 PM
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FYI,
The VF22 is the largest VF turbo with a 48mm compressor housing and a 5 blade compressor wheel. The exhaust housing is a P20. This is the standard turbo on STi Version 2 (1996) and first 100 of the 22B (1998).
The VF23 is similar to the VF22 but the compressor housing is 46mm and incorporates a 7 blade design compressor wheel. The exhaust housing is the same as the VF22. This is the standard turbo on the STi Version 3 (1997).
The VF29 is similar to the earlier VF28. The compressor housing is 46mm and incorporates a 7 blade compressor wheel. The exhaust housing is a quicker spooling P18. This is the standard turbo on the STi Version 6.
The VF30 has a bigger compressor than the VF23 at 47mm. It incorporates a 9 blade compressor wheel. The core is a divided thrust bearing and has a P18 exhaust housing. This is the standard turbo on the New Age Sti.
The VF34 is similar to the VF30 but has improved spool up due to roller bearing design. This is the standard turbo on the New Age Sti RA Spec C.
The VF35 has identical internals as the VF30 and it uses divided thrust bearings. However, the exhaust housing is a P15 which means this turbo will have fantastic spool characteristics. This turbo is standard on the new WRX Type RA.
The VF22 is the largest VF turbo with a 48mm compressor housing and a 5 blade compressor wheel. The exhaust housing is a P20. This is the standard turbo on STi Version 2 (1996) and first 100 of the 22B (1998).
The VF23 is similar to the VF22 but the compressor housing is 46mm and incorporates a 7 blade design compressor wheel. The exhaust housing is the same as the VF22. This is the standard turbo on the STi Version 3 (1997).
The VF29 is similar to the earlier VF28. The compressor housing is 46mm and incorporates a 7 blade compressor wheel. The exhaust housing is a quicker spooling P18. This is the standard turbo on the STi Version 6.
The VF30 has a bigger compressor than the VF23 at 47mm. It incorporates a 9 blade compressor wheel. The core is a divided thrust bearing and has a P18 exhaust housing. This is the standard turbo on the New Age Sti.
The VF34 is similar to the VF30 but has improved spool up due to roller bearing design. This is the standard turbo on the New Age Sti RA Spec C.
The VF35 has identical internals as the VF30 and it uses divided thrust bearings. However, the exhaust housing is a P15 which means this turbo will have fantastic spool characteristics. This turbo is standard on the new WRX Type RA.
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