STI 7 Boost Spikes
18 February 2003, 06:44 PM
#1
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Sorry if this topic has been discussed million of times, but I haven't been reading this forum recently.
I have a decatted STi 7 and was wondering if someone finally solved this problem? Is it the wastegate diameter or there's something else?
Nick
I have a decatted STi 7 and was wondering if someone finally solved this problem? Is it the wastegate diameter or there's something else?
Nick
19 February 2003, 12:59 AM
#2
Gevor,
Do a search, there's loads on this on here. IIRC you need to fit a new restrictor to the turbo, and get an electronic gizmo to get rid of the CEL. Search will give you more definite info on all this.
Please be careful; if you read some more you will see that there are stories on here of 7's blowing up with knackered pistons (most probably due to fuel leaning out). You may wish to consider remapping with the decat system in place to be safe.
However I am no expert and am going purely on memory.
Search it is!
WB
Do a search, there's loads on this on here. IIRC you need to fit a new restrictor to the turbo, and get an electronic gizmo to get rid of the CEL. Search will give you more definite info on all this.
Please be careful; if you read some more you will see that there are stories on here of 7's blowing up with knackered pistons (most probably due to fuel leaning out). You may wish to consider remapping with the decat system in place to be safe.
However I am no expert and am going purely on memory.
Search it is!
WB
19 February 2003, 11:47 AM
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Thanks a lot.
I tried searching already, but haven't found anything.
The problem is that I'm using an EBC and it doesn't help at all. The only aolution that I found was fitting the silencer that came with my Blitz NurSpec R. Did anyone try making the wastegate bigger? That's what causes the spikes I believe.
Nick
I tried searching already, but haven't found anything.
The problem is that I'm using an EBC and it doesn't help at all. The only aolution that I found was fitting the silencer that came with my Blitz NurSpec R. Did anyone try making the wastegate bigger? That's what causes the spikes I believe.
Nick
19 February 2003, 12:23 PM
#4
Gevor,
You are not looking hard enough! Try these:
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=122929
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=133466
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=86426
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=95477
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=79018
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=154168
You are not looking hard enough! Try these:
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=122929
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=133466
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=86426
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=95477
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=79018
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=154168
19 February 2003, 02:29 PM
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Nick,
It´s not completely clear what you mean. If your car overboosts after the turbo spools up (3000 - 4000 RPM) that can be cured with a bigger restrictor (1.2 - 1.25 mm) in the hose from the turbo to the wastegate solenoid. (however your boostcontroller should be able to cure that problem without changing the restrictor!) If your car suffers from boost creep at high revs, the only thing what helps is increasing the wastegate diameter. (we increased it to 27 mm which works well)
If you have the standard ECU and fuel pump, try to keep the boost under 1.0 bar after 6.000 RPM otherwise your mixture will be too lean!
Mark.
It´s not completely clear what you mean. If your car overboosts after the turbo spools up (3000 - 4000 RPM) that can be cured with a bigger restrictor (1.2 - 1.25 mm) in the hose from the turbo to the wastegate solenoid. (however your boostcontroller should be able to cure that problem without changing the restrictor!) If your car suffers from boost creep at high revs, the only thing what helps is increasing the wastegate diameter. (we increased it to 27 mm which works well)
If you have the standard ECU and fuel pump, try to keep the boost under 1.0 bar after 6.000 RPM otherwise your mixture will be too lean!
Mark.
19 February 2003, 02:41 PM
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EMS, thanks a lot. My car has a boost controler installed and it doesn't cope with the boost spikes. After 5.000rpm boost rises up to 1.3bar. I was thinking of make a wasyegate bigger, but I need some help from someone who tried that already. Did you just make the hole bigger or you also changed the plate that shuts the wastegate? What is the standard wastegate diameter? What changes exactly did you see after doing that?
Nick
Nick
19 February 2003, 03:23 PM
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I am suprised that your turbo still spikes after the fitting of an EBC. I have a MRT EBC and the boost holds rock steady at the selected boost level. Are you sure the EBC is working properly. In SA we have found that with a Decat and an EBC the boost spike problem is solved and we have had no failures to date.
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19 February 2003, 03:45 PM
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The more I hear from you the more I am convinced that you have a problem with that EBC. I am one of the unfortunates that had an engine failure due to boost spikes and had a rebuild after only 4000 km's. You are running a serious risk with those spikes and if your turbo is a vf35, I think it is only safely rated to about 1.1bar. You should consider having that EBC checked or get hold of a MRT EBC they are simple and 100% reliable.
Mike
Mike
19 February 2003, 03:58 PM
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Mike,
read the treads as stated above! (it has nothing to do with the boost controller!) Not every car and exhaust system have the same behaviour.
Nick,
We only increased the diameter of the wastegate to 27 mm (AFAIK the standard diameter is 24.5 mm). We are able to hold a stable 1.0 bar until 7.500 RPM in 5th gear. (even at -8°C)
Mark.
read the treads as stated above! (it has nothing to do with the boost controller!) Not every car and exhaust system have the same behaviour.
Nick,
We only increased the diameter of the wastegate to 27 mm (AFAIK the standard diameter is 24.5 mm). We are able to hold a stable 1.0 bar until 7.500 RPM in 5th gear. (even at -8°C)
Mark.
19 February 2003, 04:00 PM
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Mike, thanks for your replies. I'm using and insert that comes with my backbox, it helps prevent the boost spikes. I'm also running an additional 250 l/h fuel pump and a fuel pressure regulator, so no concern about leaning out.
What I'm trying to do is get rid of the problem for good. A lot of people on this forum are fitting restrictors, putting back stock frontpipes etc., but noone knows for sure what causes those spikes.
What I'm trying to do is get rid of the problem for good. A lot of people on this forum are fitting restrictors, putting back stock frontpipes etc., but noone knows for sure what causes those spikes.
20 February 2003, 06:09 AM
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Sure Mark with these things it can be a number of reasons I am not even aware of what mod's are on the car. I am only saying I am suprised a EBC is not responding at all and I am saying what worked for us.
As for -8 degrees we don't even get that in our freezers where I come from ;-)
As for -8 degrees we don't even get that in our freezers where I come from ;-)
20 February 2003, 08:15 AM
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Gevor
We do know for sure what is causing the spikes. The boost control maps are designed for the laggy spool up that is achieved with the standard exhaust. Before the ECU sees the actual boost pressure at the manifold pressure sensor (MAP) the boost must pass through a small restrictor. This restrictor has a delaying effect on what the ECU sees.
When you fit a de-cat system the turbo spools MUCH more quickly and the boost control maps are just too slow to react in time so the boost overshoots the target.
By changing the boost control restrictor from 0.9mm to 1.25mm the increase in pressure is seen by the manifold pressure sensor much more quickly and the boost control maps can react in time to stop the boost spikes.
We do know for sure what is causing the spikes. The boost control maps are designed for the laggy spool up that is achieved with the standard exhaust. Before the ECU sees the actual boost pressure at the manifold pressure sensor (MAP) the boost must pass through a small restrictor. This restrictor has a delaying effect on what the ECU sees.
When you fit a de-cat system the turbo spools MUCH more quickly and the boost control maps are just too slow to react in time so the boost overshoots the target.
By changing the boost control restrictor from 0.9mm to 1.25mm the increase in pressure is seen by the manifold pressure sensor much more quickly and the boost control maps can react in time to stop the boost spikes.
20 February 2003, 09:23 AM
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Pete, then how come removing the restrictor and installing the EBC has no effect? As far as I understand the wastegate diameter is too small to let the exhaust gasses bypass the turbine. Even with the BC switched off (actuator connected to turbo outlet) you can still see the boost rise up to 1.2 or 1.3 bar, isn't it supposed to be 0.6 or a bit more? Another thing I noticed: I usually see the spikes after 4.500-5.000rpm, isn't that when the cams switch to a different profile? Can the variable valve timing also cause it?
20 February 2003, 09:31 AM
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Gevor
Lets go back a step then.
Are you seeing "spikes" to 1.2/1.3 bar or is the boost gradually creeping up to these levels?
A totally standard STi7 will spike to 1.3 bar when floored in 5th at 4500 rpm, due to the slow boost control. As the car does this in standard form, we can hopefully assume that it is not a problem.
If it is boost creep (the boost gradually rises to these levels as the revs increase), follow Mark's (EMS) advise about porting the wastegate or consider a different downpipe design, if you have changed this.
Lets go back a step then.
Are you seeing "spikes" to 1.2/1.3 bar or is the boost gradually creeping up to these levels?
A totally standard STi7 will spike to 1.3 bar when floored in 5th at 4500 rpm, due to the slow boost control. As the car does this in standard form, we can hopefully assume that it is not a problem.
If it is boost creep (the boost gradually rises to these levels as the revs increase), follow Mark's (EMS) advise about porting the wastegate or consider a different downpipe design, if you have changed this.
20 February 2003, 01:47 PM
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I *COULD* be mistaken, but...
... when SBC-iD is fitted, and it is switched off, shouldn't the turbo only spool up to the stock wastegate spring rate? Which is around 0.60bar.
I know mine does that (SBC-DC, not exactly the same, but same solenoid).
I'd say something's wrong with the EBC.
... when SBC-iD is fitted, and it is switched off, shouldn't the turbo only spool up to the stock wastegate spring rate? Which is around 0.60bar.
I know mine does that (SBC-DC, not exactly the same, but same solenoid).
I'd say something's wrong with the EBC.
20 February 2003, 01:55 PM
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GDB, you're right, it's supposed to be around 0.6bar. Nothing's wrong with the solenoid. I've seen STIs with SBC i-D and SBC DC fitted, no difference, all experience overboost.
