Dave T-S

More feedback.......

I did some more exhaust swopping today....

Carolyn's car - I put the rest of the OEM exhaust back on - it now has the OEM exhaust from the turbo back, plus ScoobySport up-pipe. Result? It still spikes to 1.4/1.45 bar, and holds around 1.15 to 1.2 bar (in 4th to 6th gears).

I put the ScoobySport centre and backbox on mine. This now has OEM up and downpipes, with ScoobySport system from downpipe back (so one cat taken out). It peaks at 1.3 bar, and holds around 1.15 bar in 4th to 6th gears. Goes and sounds better too

I am still convinced the up pipe is the villain of the piece, not the downpipe. Definitely together they are causing the 1.7 bar spikes, but I have a feeling that the decat downpipe with OEM up pipe is probably not too bad.

I guess the acid test would be to put the ScoobySport downpipe that is lying in the garage on mine, so it has OEM up pipe, and full decat from turbo back, and see.....however, are going to try the PPP on both cars so will probably fit this first (it is possible the PPP *might* have a replacement downpipe with a sports cat fitted, but I do not think the final spec is signed off yet).

[Edited by Dave T-S - 4/1/2002 4:51:07 PM]

Paul N P

The STI UK refered to by Matt above sounds very much like mine.

Fitted a full Power Engineering T75 system with high flow sports cat. Very impressed by the service given by PE, the quality of the T75 and the performance/sound improvement. Everything else completely standard at the moment, incl. OEM up pipe.

Boost spike also easily resolved by PE with restrictor and confirmed using data monitoring by Steve of ECUTEK, on dyno and road test. Thanks for this guys! Very impressed also by ECUTEK software, made this problem very easy to diagnose, resolve & test!

As mentioned before car peaking @ 1.26bar and holding 1 bar, performance difference with PE system vs. OEM is like driving 2 completely different cars.

Car was dyno'd @ 311bhp prior to restrictor then @ 300bhp 288lbft after. Peak power at 7450rpm. Pretty hot day as well!

I'm considering PE up pipe & GGR induction kit next, I'm a bit worried about up pipe based on previous comments. Should I be??


[Edited by Paul N P - 4/3/2002 5:53:57 PM]

john banks

If you use a needle valve you will find a sweet spot where it is perky and just reaches and holds target boost without a significant peak. If you dial in a peak in warm conditions it will go ape when it is cold. Boost spikes seem pretty bad for causing detonation.

[Edited by john banks - 7/3/2002 9:41:56 AM]

BretMan

I have a JDM STi VII and I am about to fit a decat exhaust including ScoobySport downpipe. Having followed the thread about boost spiking up to 1.7 Bar with this setup, I am a bit reluctant to go ahead without a fix.

I want to retain the factory ECU control of boost (when within normal limits) and make the minimum of modifications necessary to keep boost within stock levels.

My idea is to bypass the factory control of the wastegate in boost spike situations so it responds quickly enough to avoid overly high boost.

The diagram shows how it might work:



The idea is that the pressure control valve would be set to open at just over the factory boost setting (e.g. 1.25 bar) so that as soon as the boost reaches that level, the wastegate is immediately opened by bypassing the boost control solenoid and factory restrictor.

Not being overly technical, I would be interested as to what people think...

Would this work?



[Edited by BretMan - 3/19/2002 10:14:52 PM]

BretMan

... the image now appears correctly! ...

[Edited by BretMan - 3/19/2002 10:15:50 PM]

john banks

In earlier cars the restrictor is on the manifold side of the T-piece - is the STi 7 different?

You could consider a relief valve which would be a single valve solution (ball moves off spring at high pressure).

Possible problem- the relief valve would be at lower pressure than manifold pressure due to the bleed effect of the wastegate solenoid.

Has anyone tried just enlarging the orifice in the restrictor? This is how most sort out boost peaks on the older models. Perhaps you've already thought of that.

How about a boost controller? Electronic could give much better control.

Or even a manual boost controller and disconnect the solenoid? No ECU control over boost though, and boost curve may be too flat without the usual tapering that is often engineered in at high revs. Works on older Scoobies, MY01 WRX and Evo 7 though

RT

1. The restrictor is indeed on the other side of the factory T joint - ie on the side nearer the turbo compressor.

2. I have tried enlarging my orifice from 0.75 to 0.9mm. There doesn't seem to be a reduction in boost peak or held boost. I'm also beginning to think the boost control is indeed closed loop.

3. I know someone who runs a Greaddy Profec with a decat downpipe. Altho I have not been in his car personally, he reports that he's managed to control his spikes (he was also seeing 1.7bar), and that his boost is now around 1bar repeatably.

Hope this helps.

BretMan

The concern with using a EBC or a Dawes Device is that they don't have the boost taper (as you mention, John).

The standard boost tapers off quite steeply (this image is off APS's site):



So I wonder if the fuelling would still be okay?

RT: how did your friend connect the electronic boost controller - was it replacing the factory boost control solenoid, or in addition to it as I was suggesting above?

In the other thread, an increase of the restrictor diameter to 1.0mm apparently did have an effect, but are there any downsides to this mod. - does it affect your throttle response?

Thanks...

Dave T-S

Grant cured his with a 1.0mm restrictor. Carolyn's is booked in at ScoobySport (April 6th) for the same, plus fitting a boost gauge to keep an eye on it. Will keep you posted.

Personally I would prefer to keep the same method of boost control that Subaru do.

BretMan

Yep, I agree... especially while the car is under warranty. I think Subaru may take a dim view of any boost control mod. that has the potential to run higher than stock boost.

I think I will go ahead with the downpipe and try the 1mm restrictor with a boost gauge... further mods can come later if needed...

Anyone who has a boost gauge know what the boost spikes are with a stock exhaust?

Dave T-S

Bretman - LOL - re the warranty, here of course we have the novel situation of a boost control device that is designed to REDUCE boost

Re boost spikes with a stock exhaust - I would not have thought Subaru would have allowed the cars out of the factory with any sort of significant spikes - could be wrong though.....

rs

I have a scoobysport decat system to go on my UK STI, is the restrictor something that is easily fitted or is it worth a trip to scoobysport to have it done?
I don't really want to fit the exhaust until the spike issue is sorted.

Cheers
RICH

Dave T-S

It's a five minute job to change the restrictor.....just replaces the one already fitted in the tube from the wastegate actuator to the boost control solenoid. ScoobySport are having some made up.

My email exchange with Grant is at home, but if I remember correctly you can also use a Weber DGAV carb 1.00mm jet for the restrictor, I may get hold of one in the meantime and fit it plus the boost gauge to Carolyn's, priot to taking mine to ScoobySport for the exhaust.

Dave T-S

Just to add to my earlier post (partly my memory going and partly having spoken to Dirk at Powerstation in the meantime), Grant's spiking was not totally cured by the 1mm restrictor, but it did calm things down. A Dawes device was also added.

RT

BRETMAN,
My friend that's running the EBC says:

"The EBC is a replacement of the factory solenoid, that means my factory solenoid is still connected, but runs as a dummy. The EBC takes over all boost controls as an independent system.

The hose that tap off the compressor's end is connected to the EBC. Same goes for the wastegate's end.

Nothing is connected anymore. You may also remove the factory solenoid, but i am not sure if any ckeck light will come on."


Hope this helps. He reports that it has definitely stopped the 1.7bar spiking. He now sees just above 1bar reliably.

RT

Bretman,
My exhaust is completely stock, cats and all. MY01 STI RA. The spikes I see depend greatly on conditions at which WOT is given.

1. Standing start, gear 1, WOT. I see about 1.1bar in first gear, and just above 1bar in subsequent gears.

2. Rolling constant speed, gear 2, 3000rpm. On sudden application of WOT, boost spikes higher, just above 1.2bar falling back at higher rpms. Subsequent shifts to gears 3 and 4 see the boost not spiking and holding at just above 1 bar.

3. Rolling constant speed, gears 3 or 4, 3000rpm. WOT gets me almost 1.4bar. I don't know for how long cos I chickened out (not wanting a blown engine) and backed off the throttle.

I strongly suspect that on the first WOT "pull", the boost solenoid has a different routine to subsequent WOT's. Maybe this is to allow the boost to build faster for the first spool up. This would explain why in case (1) gear 3 WOT boost is only 1bar; whereas in case (3), gear 3 WOT boost is almost 1.4bar. Opinions?

john banks

The boost pressure on the graph does drop quite sharply. I don't think a Dawes would completely flatten it - depends on the actuator.

On the MY00 UK and the MY01 US the solenoid can be replaced by a 10K resistor if you want to remove it when running an MBC/EBC. But you can also just disconnect it pneumatically and leave it there clicking away.

The Apexi AVC-R is the only boost controller I am aware of that will allow you to map boost by RPM. The Blitz and HKS EVC IV do not. I believe the HKS EVC Pro might do the RPM mapping.

The Dawes may be worth a go if you can see what your fuelling and knock are doing, as well as injector times. You may get some performance to boot, but it is new ground.

Of course there are warranty and ECU boost control preferences I hear all that.

Dave T-S

RT
I believe it's a gearing/load issue. Carolyn's STi only spikes in the higher gears not 1st-3rd - there is more load when accelerating in 4th-6th doe to the higher gearing.

[Edited by Dave T-S - 3/20/2002 1:36:46 PM]

RT

Dave, yes I agree about the different loads in different gears.

But that would not explain why WOT in gear 3 after pulling hard in gears 1 and 2, the boost only peaks at 1bar.

But if you are at a constant speed in gear 3 light throttle, and then floor it, you get a 1.4bar spike.

This sounds like different solenoid routines to me.

Mike Tuckwood

Boost is load related. 01MY STi RA should be running (apparently) up to 1.5 bar as standard.

mutant_matt

So what's the held boost on an un-modded STi then? 1 bar?

Matt

Dave T-S

Tell you when I get the gauge on mine this weekend.......

GMS

As Dave says I had changed the restrictor size to a 1.00mm.
These are available from Southern Carbs 020 8540 2723 in Wimbledon.
Unfortunatley the size of the restrictor alone did not stop the boost spiking but it did reduce the level it reached.This was not a perfect solution.
I have now fitted a Dawes device and yesterday took it to PE to put on their rollers.
At first we checked the fuelling through the rev range and it was spot on, although I am running it with a Unichip(fitted by Powerstation) so this may be not indicative of the way a standard car fuels.
The car was mapped with quite a lot of retard on the ignition as when we altered the fuelling high in the rev range the car started to det.
After about 1hr on the rollers we incresed the boost till it held appox 1.2bar and the car was still running well with good feulling and no det.I ran out of time but Mervin felt that the car still had more to come as at 6000rpm the bhp curve leveled of,due possibly to the timing.
I plan to get this sorted I the near future but after nearly two hours on the rollers and the car getting very hot it produced 307bhp and 280lbft which I am very pleased with.
I would sugest that changing the restrictor can only be a temporary fix until a better solution is found.
And with this in mind may now fit something along the lines of an EVC to control it but will look for a bit more advice before doing so.
Changing the exhaust on this car is not as simple as on my old MY00 the after affects seem to be far ranging.
So take care if you are thinking of de-catting the car.

Grant

GMS

As Dave says I had changed the restrictor size to a 1.00mm.
These are available from Southern Carbs 020 8540 2723 in Wimbledon.
Unfortunatley the size of the restrictor alone did not stop the boost spiking but it did reduce the level it reached.This was not a perfect solution.
I have now fitted a Dawes device and yesterday took it to PE to put on their rollers.
At first we checked the fuelling through the rev range and it was spot on, although I am running it with a Unichip(fitted by Powerstation) so this may be not indicative of the way a standard car fuels.
The car was mapped with quite a lot of retard on the ignition as when we altered the fuelling high in the rev range the car started to det.
After about 1hr on the rollers we incresed the boost till it held appox 1.2bar and the car was still running well with good feulling and no det.I ran out of time but Mervin felt that the car still had more to come as at 6000rpm the bhp curve leveled of,due possibly to the timing.
I plan to get this sorted I the near future but after nearly two hours on the rollers and the car getting very hot it produced 307bhp and 280lbft which I am very pleased with.
I would sugest that changing the restrictor can only be a temporary fix until a better solution is found.
And with this in mind may now fit something along the lines of an EVC to control it but will look for a bit more advice before doing so.
Changing the exhaust on this car is not as simple as on my old MY00 the after affects seem to be far ranging.
So take care if you are thinking of de-catting the car.

Grant

GRANT

Matt,
You are spot on apparently it is 1bar.
Give me a call tommorrow have an interesting proposition for you.

Grant

BretMan

Right... that's it. I'm leaving it stock until I can save some more money.

I just spoke with Possum Bourne motorsport - they said that 1.7 Bar is unheard of, and recommend that the best solution is to go the full hog and get a PossumLink and fully dyno tune the car.

Sounds like the safest idea, but I can't afford it now, :-( so it'll have to wait unless a decent fix comes from Pete at SS.

BTW, the PossumLink for the new STI is due in about a week or two - they are just sorting out the variable valve timing part of the mapping...

RT

I agree the standard held boost is approx 1 bar. But for all those who have not tried, try this:
Put the car in 3rd gear and drive half throttle at a constant 3000rpm. The give it WOT suddenly and watch the boost gauge (or better, use DEFI's recording function). You are sure to see at least 1.3bar.

Funny thing is, the boost on my previous GC rex (MY99) 220hp was never this dependant on gear / load. The most it fluctuated on full throttle was <1bar between hot/cold days and gears 1/2/3/4.

T5NYW

iTrader: (4)

I was thinking of Full De-cat ( magnex )my new UKSTi7 and spoke to a one tuner supplier said due to DP & full cat removal at constant running along motorway, for instance, you could get engine light to come on. But said it's only a warning from the Lambada!!! emissions sensor after DP cat and would cost £50 to put right
Question is this the same fault as your discussing and is it worth the hassle??. Can I go middle of the road leave DP nad 2 cats alone, Put cat-bypass pipe and new Silencer without any of the above issues.

Tony

LitchfieldImports

I've been running our demo for sometime now with a full exhaust system and I have not had any problems with the check engine issue. The exhaust set-up on the STI is different to the WRX though.

Good results Grant, mirrors what mine has

Iain

BretMan

Tony:

No, the boost spiking is a different issue.

Regards the CEL - that is just an error code apparently caused by the different reading of the rear O2 sensor resulting from there being no cat in the system.

The £50 box of tricks is a sensor simulator from SS that pretends to be the rear sensor so the ECU thinks all is okay.

Not sure whether it is needed on the STi or not? Certainly is on the WRX 01/02.

Bret