Decat STI - Boost Spike Fix Idea - Feedback?
27 March 2002, 01:54 PM
#63
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Matt, yes the gear is significant here.
1.26 bar peak and just under 1 bar held sounds like a gear 2 scenario with std exhaust.
first gear i see a just above 1.1 bar peak. don't really know the "held" as everythings happening so fast. Used the peak hold function on the defi gauge.
1.26 bar peak and just under 1 bar held sounds like a gear 2 scenario with std exhaust.
first gear i see a just above 1.1 bar peak. don't really know the "held" as everythings happening so fast. Used the peak hold function on the defi gauge.
27 March 2002, 04:50 PM
#64
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John,
As far as I'm aware, the trace info that you can download is real data. I spoke to Steve and the STi 7 in question has a full PE Decat exhaust and nothing else but the restrictor was changed to cure overboosting. The run was done (Steve thinks) in 4th so the levels are probably due to the restrictor size.
RT, why not get a passenger to sit in and report the peak and held that the gauge reports?
Matt
As far as I'm aware, the trace info that you can download is real data. I spoke to Steve and the STi 7 in question has a full PE Decat exhaust and nothing else but the restrictor was changed to cure overboosting. The run was done (Steve thinks) in 4th so the levels are probably due to the restrictor size.
RT, why not get a passenger to sit in and report the peak and held that the gauge reports?
Matt
28 March 2002, 12:43 AM
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Unable to find a crazy enought passenger! Haha!
I guess I never really got down to it. I'm not racing competitively, and my interest in this topic is from the longevity point of view. I had thought the spiking was a contributing factor to my occassional det.
I'm probably in the minority here, but I do honestly feel that the car's "fast enough". *flame suit on*
In the tropics, heat is a major problem - some days can be >35degC out, so most of my attention/funding will be focussed on cooling.
(already have HKS oil cooler and boot i/c spray tank installed, now sourcing for high pressure pump for the latter)
Oh, and not having enough money to replace a blown engine makes me err on caution!
I guess I never really got down to it. I'm not racing competitively, and my interest in this topic is from the longevity point of view. I had thought the spiking was a contributing factor to my occassional det.
I'm probably in the minority here, but I do honestly feel that the car's "fast enough". *flame suit on*
In the tropics, heat is a major problem - some days can be >35degC out, so most of my attention/funding will be focussed on cooling.
(already have HKS oil cooler and boot i/c spray tank installed, now sourcing for high pressure pump for the latter)
Oh, and not having enough money to replace a blown engine makes me err on caution!
02 April 2002, 12:24 AM
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My car is in next week to have the SS downpipe put in place with a custom centre section (with resonator) and stock STI back box. (retains stock uppipe)
The installer (Maclennan Performance, NZ) claims that they can address the spiking by lengthening the actuator slightly and having researched this a bit, it seems likely to work.
I'm also fitting a Blitz Dual Turbo Timer/DIgital Boost Gauge with peak hold, so I'll report back what the result is.
PS Anyone had any experience with the Blitz? - is it very accurate? Seemed quite good as you can set it to turn bright red if you hit a preset boost level (spike).
The installer (Maclennan Performance, NZ) claims that they can address the spiking by lengthening the actuator slightly and having researched this a bit, it seems likely to work.
I'm also fitting a Blitz Dual Turbo Timer/DIgital Boost Gauge with peak hold, so I'll report back what the result is.
PS Anyone had any experience with the Blitz? - is it very accurate? Seemed quite good as you can set it to turn bright red if you hit a preset boost level (spike).
03 April 2002, 08:40 PM
#71
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Paul
My bog standard UK STi7 is peaking at 1.3 bar and holding 1.1 to 1.15. That's a very expensive way you have taken to get a reduction in boost!
Regarding the up pipe, be VERY careful. It appears from my experience to be a bigger problem than the downpipe. With replacement up pipe, but totally OEM system from turbo back, spiking to 1.5 bar, surging and generally driving very badly.
My bog standard UK STi7 is peaking at 1.3 bar and holding 1.1 to 1.15. That's a very expensive way you have taken to get a reduction in boost!
Regarding the up pipe, be VERY careful. It appears from my experience to be a bigger problem than the downpipe. With replacement up pipe, but totally OEM system from turbo back, spiking to 1.5 bar, surging and generally driving very badly.
05 April 2002, 07:52 AM
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Chaps,
FYI - I have been thinking about getting a full APS system for my STi when it arrives and APS say that with their system, there is no problems with boost spiking.
Will be interesting to see what "no problems" means but APS are usually very good with their mods and they do a lot of proper R&D before products go out the door.
The exhaust is a full system (all or nothing) as it's not designed to bold onto any other system, has a high flow sports cat and a small muffler. So it's emission friendly, not too loud, no drone on the motorway but is good for 350bhp
Matt
FYI - I have been thinking about getting a full APS system for my STi when it arrives and APS say that with their system, there is no problems with boost spiking.
Will be interesting to see what "no problems" means but APS are usually very good with their mods and they do a lot of proper R&D before products go out the door.
The exhaust is a full system (all or nothing) as it's not designed to bold onto any other system, has a high flow sports cat and a small muffler. So it's emission friendly, not too loud, no drone on the motorway but is good for 350bhp
Matt
06 April 2002, 10:52 AM
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Dave T-S,
You seem to have a good point, however my boost figures above came from ECUTEK data logging software, my boost gauge suggests similar boost figures to those you are seeing on your STI. Also, I'm not sure how accurate boost guages are, accuracy will of course vary from one manufacturer to another.
Boost readings aside, the performance difference before and after fittng the PE system (vs. OEM) is absolutely incredible and once the restrictor was fitted the car was again noticably quicker. This is down to this giving me an extra 15bhp & 15 lbft from 4000 thro to 6500rpm, this is complemented by a much smoother delivery of power from 4000 all the way thro to the limiter.
All in all, I'm well chuffed with the results of my efforts!
On another note, I'm possibly thinking of fitting an induction kit as I mentioned in earlier thread. I realise that this may cause an element of lean running a low revs, can this be sorted out without messing around with Unichips, re-mapping etc etc..? Your advice very much appreciated.
Paul
You seem to have a good point, however my boost figures above came from ECUTEK data logging software, my boost gauge suggests similar boost figures to those you are seeing on your STI. Also, I'm not sure how accurate boost guages are, accuracy will of course vary from one manufacturer to another.
Boost readings aside, the performance difference before and after fittng the PE system (vs. OEM) is absolutely incredible and once the restrictor was fitted the car was again noticably quicker. This is down to this giving me an extra 15bhp & 15 lbft from 4000 thro to 6500rpm, this is complemented by a much smoother delivery of power from 4000 all the way thro to the limiter.
All in all, I'm well chuffed with the results of my efforts!
On another note, I'm possibly thinking of fitting an induction kit as I mentioned in earlier thread. I realise that this may cause an element of lean running a low revs, can this be sorted out without messing around with Unichips, re-mapping etc etc..? Your advice very much appreciated.
Paul
06 April 2002, 02:17 PM
#74
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Paul
I think I am probably misled in what I said - just because your setup appears to be giving less than standard boost doesn't mean there aren't gains
As far as an induction kit is concerned, I'm not sure if anyone has fitted one to an STi7 yet, I guess the answer is if you have the means to check the boost and fuelling, then chuck one on and see what effect it has!
I think I am probably misled in what I said - just because your setup appears to be giving less than standard boost doesn't mean there aren't gains
As far as an induction kit is concerned, I'm not sure if anyone has fitted one to an STi7 yet, I guess the answer is if you have the means to check the boost and fuelling, then chuck one on and see what effect it has!
06 April 2002, 09:49 PM
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With regards to the APS system.
The exhaust is full emissions compliant ( inc sports cat)and does not include changing the up pipe.
They have noticed no spiking which they can only presume comes from replacing the up-pipe.
They are looking into a de-cat down pipe due to strong demand.
Also they have just produced a 400bhp or 300kw system for the STi7 which at the moment is undergoing trials but has already posted
0-100 times to match a 911 turbo.
It seems down under they are well ahead of us.
There has been a test of the 250kw system and the car posted a
0-100km time of 4.2sec which is very impresive considering the car weighs 1490kg.
Grant
The exhaust is full emissions compliant ( inc sports cat)and does not include changing the up pipe.
They have noticed no spiking which they can only presume comes from replacing the up-pipe.
They are looking into a de-cat down pipe due to strong demand.
Also they have just produced a 400bhp or 300kw system for the STi7 which at the moment is undergoing trials but has already posted
0-100 times to match a 911 turbo.
It seems down under they are well ahead of us.
There has been a test of the 250kw system and the car posted a
0-100km time of 4.2sec which is very impresive considering the car weighs 1490kg.
Grant
07 April 2002, 09:41 AM
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Could be, but weren't RT's compatriots in Singapore getting 1.7 bar spikes also with just a decat and downpipe?
The other variable could also be the type of downpipe. The twin dump pipes have previously been reported to cause boost instabilities due to backpressure on the wastegate caused by the plate separating the wastegate and exhaust pipe.
RT: do you know if they were running uppipes, or just downpipe and decat, and if so were they twin dump or single pipe downpipes? - Thanx
The other variable could also be the type of downpipe. The twin dump pipes have previously been reported to cause boost instabilities due to backpressure on the wastegate caused by the plate separating the wastegate and exhaust pipe.
RT: do you know if they were running uppipes, or just downpipe and decat, and if so were they twin dump or single pipe downpipes? - Thanx
07 April 2002, 10:09 AM
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To the best of my knowledge, the setup was downpipe only. Up pipe standard. After all, the JDM STI doesn't have an uppipe cat.
1. One chap has a twin downpipe (2 separate "tubes", like the power engineering variety),
2. another has a single large chamber but with a "wall" seperating the wastegate gases from the turbine gases (like the MRTrally variety),
3. and the last has a decat pipe with the so-called poorer design of leaving the blanking plate in front of the wastegate (much like the std cat).
(1) and (2) definitely reported 1.7bar spikes. (3) reports spikes just under 1.7bar.
Aside: Just had the car Zaino'ed this morning! Excellent results!
1. One chap has a twin downpipe (2 separate "tubes", like the power engineering variety),
2. another has a single large chamber but with a "wall" seperating the wastegate gases from the turbine gases (like the MRTrally variety),
3. and the last has a decat pipe with the so-called poorer design of leaving the blanking plate in front of the wastegate (much like the std cat).
(1) and (2) definitely reported 1.7bar spikes. (3) reports spikes just under 1.7bar.
Aside: Just had the car Zaino'ed this morning! Excellent results!
07 April 2002, 10:36 AM
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Could be onto something here...
The Scoobysport downpipe has one opening with no divider. I suspect that any downpipe with a separator could be contributing to boost spiking.
SO... maybe either a split downpipe, or an uppipe is a contributing factor...
Hey Dave, what about trying just the downpipe and decat. without the uppipe... (or perhaps you already have and I missed it in the huge number of permutations you have already worked through?!!!) ;-)
RT - did you get some HP figures you could share with us? - strangely noone seems to have posted dyno. figures for the JDM STi yet...
The Scoobysport downpipe has one opening with no divider. I suspect that any downpipe with a separator could be contributing to boost spiking.
SO... maybe either a split downpipe, or an uppipe is a contributing factor...
Hey Dave, what about trying just the downpipe and decat. without the uppipe... (or perhaps you already have and I missed it in the huge number of permutations you have already worked through?!!!) ;-)
RT - did you get some HP figures you could share with us? - strangely noone seems to have posted dyno. figures for the JDM STi yet...
07 April 2002, 10:54 AM
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Sorry, no dyno figures. There's only one 4wd dyno on our island that I'm aware of, and its run by the local distributor for RUF (read $$$). From what I've heard, the hot air recirculation there is quite bad, so its not favoured for tuning.
07 April 2002, 12:08 PM
#80
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Bretman
LOL - standard up pipe and full decat from the turbo back is the only combination I *haven't* tried.
I heard a report that this has been done and resulted in peak boost of 1.5 bar but I would like to try it for myself.....curiosity might overcome me......
We are waiting for the PPP, so if I do put the downpipe on I shall have to take it off again, so may reach my boredom threshhold before that
Incidentally, it was mentioned above that there is no up pipe cat in the JDM STi7 - there isn't in the UK car either, but it has a sleeved expansion joint in the up pipe that reduces diameter by 5mm or so. My belief is that the removal of this restriction by fitting a plain up pipe allows a lot more exhaust gas to flow into the turbine inlet and is allowing the turbine to spin up faster, therefore catching out the standard boost control, and causing the spikes. Once the ECU gets hold of it it pulls it back to 1.15 or so held boost.
The other issue with replacing the up pipe is that Subaru put the expansion joint in for a reason. Some VERY high EGT's are going on in this area and by replacing it with a plain pipe it is liable to put expansion/contraction loads on the manifold which it wasn't designed for and in the long term is possibly going to lead to cracked manifolds or similar.
LOL - standard up pipe and full decat from the turbo back is the only combination I *haven't* tried.
I heard a report that this has been done and resulted in peak boost of 1.5 bar but I would like to try it for myself.....curiosity might overcome me......
We are waiting for the PPP, so if I do put the downpipe on I shall have to take it off again, so may reach my boredom threshhold before that
Incidentally, it was mentioned above that there is no up pipe cat in the JDM STi7 - there isn't in the UK car either, but it has a sleeved expansion joint in the up pipe that reduces diameter by 5mm or so. My belief is that the removal of this restriction by fitting a plain up pipe allows a lot more exhaust gas to flow into the turbine inlet and is allowing the turbine to spin up faster, therefore catching out the standard boost control, and causing the spikes. Once the ECU gets hold of it it pulls it back to 1.15 or so held boost.
The other issue with replacing the up pipe is that Subaru put the expansion joint in for a reason. Some VERY high EGT's are going on in this area and by replacing it with a plain pipe it is liable to put expansion/contraction loads on the manifold which it wasn't designed for and in the long term is possibly going to lead to cracked manifolds or similar.
07 April 2002, 10:11 PM
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We been running our demostrator de-cated for a while now but it also suffered overboost problems until we fitted the rest of our kit 
I'm happy to chat to anyone about it, we also fitted each of the bits in stages so we were able to see what parts had the biggest effect
Iain
01242 260406
I'm happy to chat to anyone about it, we also fitted each of the bits in stages so we were able to see what parts had the biggest effect
Iain
01242 260406
08 April 2002, 10:22 AM
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Well the rest of the kit includes the following:
Upgraded Induction Kit
Performance Exhaust System
Enhanced Engine Management Set-up (unichip)
Lowered Suspension
Up-rated Anti-Roll bar
Full Geometry Set-up
£1695+VAT fitted
The Unichip is quickly removeable with no hard wiring
Our demostrator saw 303bhp on std boost and 310 with a slight increase.
Regards
Iain
Upgraded Induction Kit
Performance Exhaust System
Enhanced Engine Management Set-up (unichip)
Lowered Suspension
Up-rated Anti-Roll bar
Full Geometry Set-up
£1695+VAT fitted
The Unichip is quickly removeable with no hard wiring
Our demostrator saw 303bhp on std boost and 310 with a slight increase.
Regards
Iain
08 April 2002, 06:17 PM
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Paul
How much did this cost you at PE. Mine comes first week in May and I cannot decide wether to go PPP or the route you heve taken. Excuse my ignorance but is OEM a stock exhast.Have you had any warrenty issues with your dealer. What do you think this engine can tolerate BHP wise before reliability becomes an issue
Steve
How much did this cost you at PE. Mine comes first week in May and I cannot decide wether to go PPP or the route you heve taken. Excuse my ignorance but is OEM a stock exhast.Have you had any warrenty issues with your dealer. What do you think this engine can tolerate BHP wise before reliability becomes an issue
Steve
08 April 2002, 07:40 PM
#88
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Pooder
OEM = original equipment manufacturer, means as you say i.e. what was fitted as standard.
BHP as such won't be the problem with an STi7 engine, it will be the sort of boost levels it is running and whether the fuel is leaning out, particularly at the top end. This will almost mean detonation, then bang!
You would have a BIG problem getting an engine blowup through the warranty with a decat exhaust, replacement chip, etc. Some Subaru dealers will not even service a car such as this.
OEM = original equipment manufacturer, means as you say i.e. what was fitted as standard.
BHP as such won't be the problem with an STi7 engine, it will be the sort of boost levels it is running and whether the fuel is leaning out, particularly at the top end. This will almost mean detonation, then bang!
You would have a BIG problem getting an engine blowup through the warranty with a decat exhaust, replacement chip, etc. Some Subaru dealers will not even service a car such as this.
08 April 2002, 09:36 PM
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Dave T-S - reading this with interest. Is the up-pipe arrangement on the MY01 the same as the STi? Reason for asking is the gasket has gone on my MY01 SS up-pipe and am wondering now if this not just a one off,had not heard of any others till now.
08 April 2002, 09:45 PM
#90
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David
Interesting.....
The OEM up pipes are different - the MY01 WRX has the cat in it, and the STi doesn't.
However, as far as I am aware the replacement up pipe is identical for both, and when used in the STi just has the exhaust gas temperature probe hole welded up (as the STi doesn't have same).
I have a theory as to the cause of the gasket blowing, will mail you offline on this.
Interesting.....
The OEM up pipes are different - the MY01 WRX has the cat in it, and the STi doesn't.
However, as far as I am aware the replacement up pipe is identical for both, and when used in the STi just has the exhaust gas temperature probe hole welded up (as the STi doesn't have same).
I have a theory as to the cause of the gasket blowing, will mail you offline on this.