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Old 05-13-2002, 05:33 PM   #1
alfriedesq
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Default STI VII boost spike mystery - can anyone in US solve the mystery>??

It seems the STI VII has serious boost spike issues . . . . (I am having them also) see :

http://www.scoobynet.co.uk/bbs/threa...threadid=80851

Is the VF30 wastegate too small ??

Is it from the AVCS????

Any ideas???
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Old 05-13-2002, 07:02 PM   #2
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Probably not the "easy fix" reply you're looking for, but since you've done so much work anyway....

I'd say its time for an external wastegate. It really would not be that hard to plumb the exhaust pipes, or if you're crazy like me you can just dump the wastegate exhaust to the atmoshere. Im pretty sure your boost spike problem would be eleminated. If not, it will sound pretty kewl

peace
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Old 05-13-2002, 07:10 PM   #3
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Try porting the wastegate first... The wastegate flapper usually overlaps the opening by quite a bit. Enlarging the opening while maintaining the flapper seal will probably fix it... if it's only an improvement... then you'll need an external wastegate.
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Old 05-13-2002, 07:12 PM   #4
Z1 Performance
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The wastegate on the VF30 is more than up to the task..

What boost controller are you runnign again? Blitz?

adam
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Old 05-13-2002, 07:32 PM   #5
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Does it have a 2 or 3 port solenoid? If 2 port like the WRX, theres your reason right there. As I understand it, the 2 port units dont control boost over 15psi well. And the STI runs at what...17psi stock.

And if your running with that SBC-ID, make sure the lines are as short as possible.

It could also be the AVCS cam switch over causing the spikes. I imagine there is a big exhaust pulse change when that happens. The over boosting might represent the moment before the ECM adjusts/switches to the new boost profile.

Ken

Last edited by DeliciouSpeed; 05-13-2002 at 07:38 PM.
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Old 05-13-2002, 08:48 PM   #6
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try a joe p mbc and your spike problem may disappear.
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Old 05-13-2002, 09:10 PM   #7
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If my memory serves me correctly a gent from britain stated thier problem stemed from the removal of thier cats.

then again my memory could be wrong. prb what you have read allready

BlitZ
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Old 05-13-2002, 09:13 PM   #8
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Quote:
If my memory serves me correctly a gent from britain stated thier problem stemed from the removal of thier cats.
I read the same thing.

Redleader
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Old 05-13-2002, 09:32 PM   #9
nhluhr
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Default Re: STI VII boost spike mystery - can anyone in US solve the mystery>??

al - i'll assume you've read Corky Bell's Maximum Boost book and you understand how boost control schemes work.

Look through chapter 12 "Boost Controls" and you'll recall that the location of the wastegate actuator signal tap can have a PROFOUND difference on the boost behavior.

If you tap it closer to the manifold, you'll see the boost rise very quickly before the wastegate opens and regulates boost. This tap location makes the response very quick but has the side effect of spiking, and exposing the signal line to more heat.

If you tap it closer to the compressor outlet, you'll see a more progressive boost curve with the wastegate cracking open earlier and holding the boost to less "spiky" behavior. This method makes the boost rise more slowly (slower response, more lag, etc) but is safer both from the standpoint of boost spiking and heat exposure.

The reason for this is the pressure differential across the intercooler and associated piping. You'll see a couple psi drop from the turbine outlet to the manifold so tapping the signal closer to the manifold means the wastegate actuator sees less boost and therefore opens later than it would otherwise.

A spring & ball type boost controller could very possibly make the problem worse by isolating the wastegate from any signal until later in the spool. If you see spiking with the factory EBC, then you need to devise a way to make the wastegate see pressure sooner and the very first post of the thread you linked seems to be a very valid way - let a little bit of pressure pass in parallel around the factory EBC so the wastegate sees it earlier and begins to crack open soon enough.

Something else that could possibly work is optimizing the size of the signal line and/or making it out of a less stretchy material. This could in effect transmit the pressure to the actuator more rapidly.

Quote:
Originally posted by alfriedesq
It seems the STI VII has serious boost spike issues . . . . (I am having them also) see :

http://www.scoobynet.co.uk/bbs/threa...threadid=80851

Is the VF30 wastegate too small ??

Is it from the AVCS????

Any ideas???
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Old 05-13-2002, 09:35 PM   #10
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Quote:
Originally posted by Blitzkrieg
If my memory serves me correctly a gent from britain stated thier problem stemed from the removal of thier cats.

then again my memory could be wrong. prb what you have read allready

BlitZ
removing cats WILL cause boost to spool faster because you're reducing backpressure significantly. This makes a greater pressure differential across the exhaust turbine which makes the compressor turbine spin up faster, thus making boost sooner than the factory solenoids/ecu know to control.
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Old 05-13-2002, 09:47 PM   #11
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Quote:
Originally posted by nhluhr


removing cats WILL cause boost to spool faster because you're reducing backpressure significantly. This makes a greater pressure differential across the exhaust turbine which makes the compressor turbine spin up faster, thus making boost sooner than the factory solenoids/ecu know to control.
It's possible that the increased air flow from the removal of the cat's could cause a boost spike.
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Old 05-13-2002, 10:44 PM   #12
alfriedesq
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The stock STI VII was makming boost spikes over there - if you follow that UK thread some guy was taking on and off diffrent combinations of intakes and exhausts including stock and he had boost spikes no matter what !

I am using the same exact stuff I was using on the WRX - same hoses - same attachment points same boost settings - same everything

and still I get boost spike with the vf30

I am thinking more and more that thye spike I am seeing has something to do with the AVCS - it will suck if it does b/c its a strong spiek and its unprediactable and will make tunning a nightmare

I can't believe all those UK guys have had this STI for so long and havn't sorted out the problem !!! This boost spike is drivbing me nuts and has to GO !

Wish could speak Japanese so i could go on a JDM forum !
Just hoping the PE 1820 is a bit more resistant to spikes than the vf30 - will know later tonight !
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Old 05-13-2002, 10:48 PM   #13
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Quote:
Originally posted by Z1 Performance
The wastegate on the VF30 is more than up to the task..

What boost controller are you runnign again? Blitz?

adam
Z-1
Blitz SBC - worked like a charm on the WRX with vf30
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Old 05-13-2002, 10:51 PM   #14
alfriedesq
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Default Re: Re: STI VII boost spike mystery - can anyone in US solve the mystery>??

Quote:
Originally posted by nhluhr
al - i'll assume you've read Corky Bell's Maximum Boost book and you understand how boost control schemes work.

Look through chapter 12 "Boost Controls" and you'll recall that the location of the wastegate actuator signal tap can have a PROFOUND difference on the boost behavior.

If you tap it closer to the manifold, you'll see the boost rise very quickly before the wastegate opens and regulates boost. This tap location makes the response very quick but has the side effect of spiking, and exposing the signal line to more heat.

If you tap it closer to the compressor outlet, you'll see a more progressive boost curve with the wastegate cracking open earlier and holding the boost to less "spiky" behavior. This method makes the boost rise more slowly (slower response, more lag, etc) but is safer both from the standpoint of boost spiking and heat exposure.

The reason for this is the pressure differential across the intercooler and associated piping. You'll see a couple psi drop from the turbine outlet to the manifold so tapping the signal closer to the manifold means the wastegate actuator sees less boost and therefore opens later than it would otherwise.

A spring & ball type boost controller could very possibly make the problem worse by isolating the wastegate from any signal until later in the spool. If you see spiking with the factory EBC, then you need to devise a way to make the wastegate see pressure sooner and the very first post of the thread you linked seems to be a very valid way - let a little bit of pressure pass in parallel around the factory EBC so the wastegate sees it earlier and begins to crack open soon enough.

Something else that could possibly work is optimizing the size of the signal line and/or making it out of a less stretchy material. This could in effect transmit the pressure to the actuator more rapidly.

I have the SBC Blitz unit wired in right from the turbo output tube on the ouput side - to the blitz unit to the wastegate

Same set up I used on the WRX

The line to measure the boost comes in off the tap for the fuel vapr recovery solioid
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Old 05-13-2002, 10:58 PM   #15
shirokuma
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On a different type of Subaru, the twin turbo B4's, we've gotten the problem also. It usually/always had to do with the exhaust - on some early B4's, even just a large cat-back muffler sometimes lead to boost spikes. This could be catastrophic for the B4's, since they don't have the block strength of the STI motor. Other common causes was to replace the centre pipe on the B4 with a higher flowing version. Basically, the computer couldn't react fast enough to shut down the spiking.

Things that have worked towards calming the spikes:
Put the exhaust system back to stock
Install a good Earthing/Grounding kit (electrical noise does seem to make the problem worse)

Paul Hansen
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Old 05-13-2002, 11:12 PM   #16
alfriedesq
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Quote:
Originally posted by shirokuma
On a different type of Subaru, the twin turbo B4's, we've gotten the problem also. It usually/always had to do with the exhaust - on some early B4's, even just a large cat-back muffler sometimes lead to boost spikes. This could be catastrophic for the B4's, since they don't have the block strength of the STI motor. Other common causes was to replace the centre pipe on the B4 with a higher flowing version. Basically, the computer couldn't react fast enough to shut down the spiking.

Things that have worked towards calming the spikes:
Put the exhaust system back to stock
Install a good Earthing/Grounding kit (electrical noise does seem to make the problem worse)

Paul Hansen
**** - going back to stock?>??? - Thats like treason to me!!!!

Also - the stock guys in UK report boost spikes also

Seems like poor engineering - -

Even if I have to put on a big mutha weategate - I got to loose that annoyance !
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Old 05-13-2002, 11:28 PM   #17
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see how the pe1820 reacts then take it from there, i have an MBC you can try if you want. Worked well when i had it on my car.
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Old 05-13-2002, 11:30 PM   #18
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Quote:
Originally posted by shirokuma
On a different type of Subaru, the twin turbo B4's, we've gotten the problem also. It usually/always had to do with the exhaust - on some early B4's, even just a large cat-back muffler sometimes lead to boost spikes. This could be catastrophic for the B4's, since they don't have the block strength of the STI motor. Other common causes was to replace the centre pipe on the B4 with a higher flowing version. Basically, the computer couldn't react fast enough to shut down the spiking.

Things that have worked towards calming the spikes:
Put the exhaust system back to stock Install a good Earthing/Grounding kit (electrical noise does seem to make the problem worse)

Paul Hansen
But earthing can't suppress noise caused by electrical equipment which comes on and off line, can it? Examples are turn signals, subwoofer load, AC clutch, cooling fans, relay and solenoid activation, etc. If earthing is a problem wouldn't these events cause problems too? Slightly off topic, but your comment about grounding and noise made me think of this. Makes me wonder how well grounded the computer is, a harness, and the piggyback Unichip. Paranoia sets in easily!
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Old 05-13-2002, 11:52 PM   #19
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Al,
Try running just off the wastegate spring for a few runs... See if it still spikes after that.

One other thing may be to lower the gain on your SBC-iD a bit.

If that doesn't work, i'd be happy to point you in the right direction of who to talk to about an external gate, but personally i think that it has to be something else...

What mode are you running the SBC-iD in? Auto or what?


-Nathan
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Old 05-14-2002, 01:15 AM   #20
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I would troubleshoot with a hpmbc from turboxs and crank open the bleed side. This will eliminate spiking...
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Old 05-14-2002, 01:56 AM   #21
alfriedesq
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Quote:
Originally posted by nmyeti
Al,
Try running just off the wastegate spring for a few runs... See if it still spikes after that.

One other thing may be to lower the gain on your SBC-iD a bit.

If that doesn't work, i'd be happy to point you in the right direction of who to talk to about an external gate, but personally i think that it has to be something else...

What mode are you running the SBC-iD in? Auto or what?


-Nathan
I was running on manuel mode and turned down the gain to ZERO - - even tried turning it OFF and the setting to 0 also - - to no avail - thanks for the hints !!!!
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Old 05-14-2002, 01:59 AM   #22
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Put the 1820 and the cusco headers and perrin custom 2" uppipe in tonight

The boost spike is GONE !!!!!!!!!!!

I think it was a combination of too much spool up at 4,000 rpm combined with the stock wastegate

The PE 1820 is spooling a bit slower AND the PE has a modified high performance waste gate actuator

What ever it was - there is no more boost spikes!!!!!

Thanks guys for all the help!
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Old 05-18-2002, 05:00 AM   #23
GDB
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Al, I want to share my experience with you:

I installed a Blitz SBC-DC boost controller a couple of days ago. So far I've been quite impressed by it: impressed by the fact that I was NOT experiencing a great deal of boost spikes as you reported.

Past few days have been very hot here, so my conservative runs were as follows:

0.90 bar held = 0.94 bar spike
1.10 held = 1.15 spike
1.20 held = 1.27 spike

When you mentioned "spike" is that what you were mentioning? I was thinking you were experiencing 0.2 bar or more "spike", is that true?. A 0.07 spike is quite OK (**IMHO**).

BTW I'm still using everything standard EXCEPT Cusco downpipe and ARC induction kit.

The Cusco downpipe itself (since it's catless) reportedly can result in 1.7 bar spike on 1.1 bar held or thereabout. Unfortunately I did NOT have boost gauge prior to the SBC-DC so I couldn't personally confirm the scary spikes reported by other STi's all over the world.

Last, I noticed smoother boost build-up with LOWER gain (around 10-ish) than higher gain (over 25). All the runs above were conducted at gain of around 10-ish. Set is currently at 65, will do some more runs when coast is clear and temps aren't as hot (aiming to get 1.30 bar held, with spiking less than 1.40).

So I'd appreciate it if you can tell us how severe your spiking was with the VF30 BIG BIG thank you in advance!!!
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