Thanks EMS, will do this weekend

But the WOT blast 0 - 120 kms through the gears must be useful as well

Cheers,
Ray

[Edited by Razor2001 - 10/4/2002 2:26:20 PM]

 

During testing an STi 7, I discovered some uncontrolled behaviour of the boost pressure. The car, with a 3" decat exhaust system fitted, suffered from rising boost pressure at high revs. (from 5.500 rpm at high loads) Even completely closing the wastegate solenoid couldn´t cure this situation. This should be caused by a restricted bypass capacity of the wastegate of the VF30 turbo.

I tested with completely closed boost solenoid: until 5.000 rpm the boost I saw was about 9 PSI, after that the boost was rising to (depending on load) 17 - 20 PSI at 7.000+ RPM.

It can be a REAL PROBLEM, as I saw boost pressures of over 20 PSI at 6.400 RPM in 6th gear, I can guarantee the car doesn´t like that at all! (testing on the German Autobahn ) In the lower gears, the load isn´t high enough to cause the problem, but in 5th and 6th gear the boost keeps rising at higher revs!

Normally (with an unmodified ECU) you should see about 12 PSI from 6.500 RPM. Even with a completely std. exhaust system I saw dropping of the wategate dutycycle to about 27%, but the boost didn´t rise.

All STi7 drivers with decat exhaust: please pay attention to this, as you can EASILY destroy your car at WOT in high gears!

I would like to hear if someone else also discovered this behaviour, and/or has DeltaDash measurements of the car. (you can easily see it in Delta Dash, as the wastegate dutycycle drops to almost zero)

Mark Verhoeven.

[Edited by EMS - 8/23/2002 10:54:21 PM]

[Edited by EMS - 8/24/2002 8:53:21 AM]

 

Yes, this was reported back in March - see here:

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

Incidentally, the STi7 has a VF35 turbo in the UK, not a VF30

 

Mark,

Why don't you try connecting the wastegate directly to the turbo exit (no solenoid), the max boost you should see is around 8 psi. If you see again spiking/higher boost than 8 psi, then probably you could conclude that the wastegate capacity isn´t enough.

Carlos H.

 

If the wastegate solenoid duty cycle is zero and enlarging the restrictor doesn't work, then porting the wastegate would be an option?

My IHI VF hybrid has this done, and it needs a pretty tight and uprated actuator to hold boost at the top like even a smaller IHI hybrid without the wastegate work.

 

Dave: I did already know the restrictor "trick" for as long as I am tuning Subaru's (from 1997). But this doesn't help as the wastegate is already fully opened.

Carlos: I did close the wastegate solenoid completely, this is the same as connecting the wastegate directly to the turbo outlet.

John: That was the idea that I had also, but I would like to hear some more expieriences from STi7 owners.

Mark.

[Edited by EMS - 8/23/2002 10:51:45 PM]

 

Mark, have you considered that the clutch may be slipping ... the symptoms you describe are classic for that.

 

Bob: The clutch was definitely not slipping. Can you explain why I should have more boost with a slipping clutch. The load on the engine is less with a slipping clutch, so I expect the boost to be lower as usual.

Mark.

 

No, as the clutch slips the load impedance allows the boost to rise higher, it only needs to be slipping in a very subtle way for this to happen, you would probably not even notice it under most conditions, believe me this happens, I must have had about seven cars that this occured during the mapping process due to the increased torque generated and I have had this on all my own cars, the std clutch just can't stand it, not worn out, when removed they almost look new apart fro the hot spots on the flywheel.

It may be a total red herring but don't dismiss out of hand.

 

Bob,

I even saw the boost rising when I was testing with completely closed boost solenoid. The boost was about 9 PSI until 5.000 rpm and after that it was starting to rise. Before the clutch definitely did not slip at 20 PSI @ 3.500 - 4.000 RPM, so I assume it doesn´t either at 9 or 10 PSI at 5.000.

The phenomenon you discribe can be a problem if you have massive torque from the midrange, starting at 9 PSI I don´t think it is caused by that.

Mark.

[Edited by EMS - 8/24/2002 9:03:00 AM]

 

EMS,

Have a read of the tread that Dave T-S mentioned as I know some people who have had your problem, and solved it with different restrictors (not idea but it does work). If the ramp up of boost is kept under control (with a different restrictor), then the OE Boost control system can just keep in check. But like you say, with the standard restrictor, with a full decat, the WG Solenoid will be working 100% DC and the boost is still rising.

Matt

 

Matt, I may be wrong, but aren't we talking about 2 separate issues here ? I always thought the restrictor is a sort of "damping" device with wich you can control/influence mid range boost and boost spikes, but doesn't have much influence on the high RPM boost ?

Mark starts off with 9 psi, so very little boost anyway. So the fact that the boost rises at high RPM must be a function of the wastegate not being able to cope with the excess gasses, and as a result more gasses flowing through the turbine, hence creeping boost.

Makes you wonder why Subaru has fitted the VF30 or VF35 in the first place ... not really brisky at low RPM and not coping with exhaust gasses at high RPM ?

Mark, what happens if you totally remove the restrictor ? Any changes ? I would guess not ?

 

This is indeed two separate problems.

Mark, you don't say what sort of downpipe the car has. Is it open neck or twin dump. There have been problems controlling the boost at high revs with some designs of twin dump downpipe, as the design can cause a restriction to the flow through the wastegate.

 

The restrictor is a kludge for low flowing solenoids.

 

One thing to try, and that would be to disconnect the actuator arm from the wastegate. This will make sure that the WG IS actually opening fully, and there are no other influences.

If by doing this, the boost drops, you'll know that there are issues elsewhere.

Mark.

 

There appears to be some confusion between opening and closing the solenoid and the wastegate itself.

If the wastegate is fully open, there should be minimal boost, and assume the wastegate flows sensibly, no boost at all.

EMS,

WHen you say you run with the wastegate closed, do you actually mean the flapper, or the solenoid?

The restrictor should do more than just damp the pressure pulses to the actuator, due to the 2 port solenoid plumbing.

Do as Mark suggests disconnect the actuator from the flapper arm, and possibly even wire it open (although exhaust pressure should open it anyway). It could be possible the actuator rod is too short, I don't know how/why it could be on a nearly new STI7, but it would contribute to the symptoms you describe.

Paul

 

I think Mark is talking about the solenoid fully closed, i.e. 0 % duty cycle (same effect as a direct hose connection between turbo nipple & wastegate actuator).

 

But the last step of disconnecting the actuator arm as Mark is saying would surely clinch it? My arm (not my arm personally - sorry) has popped off twice now on two different turbos because of insecure circlips. Both times zero boost - the wastegate just flaps open with the slightest gas flow.

It was EMS Mark who some time ago pointed out to me the error in my thinking between a closed wastegate and maximum duty cycle and he has vast experience of fiddling with these things.

I was puzzled initially when I connected a tube direct - with or without restrictor you get the same result as a zero duty cycle - roughly the strength of your actuator, unless it is binding. Presumably the 2 port can flow so little that it needs help but the restrictor alone is not enough to drop the pressure on the wastegate diaphragm significantly?

From what I understand I wouldn't be a fan of porting the wastegate unless you had to, and a small amount seems to go a long way and you could end up with dropping boost like your VF23/manifold/1 bar actuator setup - I am in that position now. If the manifold comes off and I tighten the actuator more I think I will hold boost. Have not found any leaks, and the DV is not leaking as I have changed it. Restrictive intake and pressure drop across the intercooler at high revs may also not help.

 

The car has a twin dump (3") downpipe fitted, of course the design of the downpipe will change flow through the wastegate, but I don´t think in such a huge amount. We can´t try easily another downpipe, because for that we have to change the complete exhaust system. By the way, my own MY99 VF23 Impreza has exactly the same exhaust system without these problems. (in fact with that car I had to use a 1 bar actuator to acchieve the desired boost at high revs!)

I tested the wategate actuator by hand and it´s moving nice and smooth. (and the opening angle is not restricted!)

Closing the boost solenoid means 0% dutycycle that means the wastegate actuator is directly coupled to the compressor outlet.

Mark.

[Edited by EMS - 8/24/2002 12:55:24 PM]

 

Mark

If its not the twin dump exhaust and the standard car doesn't do it, I'm interested to know what you think it is.

 

Mark (EMS), while the car was totally standard you have stated that it didn't showed this problem .....

Did the problem start as soon as you fitted the 3 inch catless exhaust system ?????, or after you modified/changed the ECU ?????

Because if you have connected the turbo outlet directly to the wastegate, and still it overboosted at high rpm's ..... then it is possible that the boost control system relies on a restriction on the exhaust system (cat. or the std. restricitve downpipe ). And now that you have fitted a 3 inch cat-less downpipe (twin dump design) it is possible that the wastegate is not upto the job.

Like Mark A. said it would be a good idea to disconnect the actuator arm to the wastegate and see what happens.

Carlos H.

 

First of all I want to tell that my goal for this topic is to give a warning to STi7 owners, because I think you can see this behaviour at every car which has an exhaust system with less back pressure. I know the car REALY likes an exhaust mod, the difference in spool up time is HUGE, but if the boost is uncontrollable rising at high loads and high revs I think you should look out very carefully for that!

I would like to hear expieriences from other STi7 owners.

Pete,

How do you think about the massive reduction in backpressure because of the lack of cats? This makes the turbo FAR more effective and to achieve the same boostpressure as standard there has to be a lot more exhaust gas flow through the wastegate. If this wastegate has a (too) small area, problems are there.

Carlos,

I am thinking exactly the same way! The wastegate capacity is hardly enough for the std. setup, if you reduce the backpressure thing are getting wrong.

Mark.

 

Ive mentioned it before, and Ive seen exactly the same problem occuring on early TD05 cars ( mine included, which was the strangest of all. My car had run for approx 2 years, perfectly with full DIY exhaust and BLitz SBC boost controller. It held 14psi all the time no probs. As the boost controller was not mine, I had to give it up eventually, after it was removed, above 5000rpm the boost would climb uncontrollably to around 20psi at 7000rpm. I have no idea why this only happened, and even leaving the wastegate completely open ( no rod attached to it ), the same overboosting occured at high revs, albeit with virtually no boost up to 5000rpm. The car had always been perfect so it really did happen out of the blue, the only thing I did was remove the blitz, and change to a pneumatic valve to control the boost )
A similar thing also happend to a friends car, after replacing his std system with a Magnex+ Scoobysport downpipe. We phoned Scoobysport ( Pete ) at the time, and he claimed he had never seen anything like that happen, they had sold hundreds of them. He would phone back if he could help. Well, with the service we got from him, we may as well went down to Kwik fit with the problem, they would have been as helpful. Thanks Pete. NOT
I have seen it happen on several cars, and the only thing we could think of is the std wastegate is too restricitve. I took the turbo off, and ported the wastegate exit on the turbocharger. On the TD05, it make a very tight 90deg turn to get to the wastegate flap. I simply smoothed out this turn, to make a good radius, and slightly enlarged the wastegate hole ( dont think that was relly necessary though. Ive since just went for the smoothing the exit, and afterwards boost control has been regained. It seems like a lot of hassle for a relatively simple problem, which doesnt happen on all cars ( WHY??? ) but it cured mine, and other people who had lost an engine due to overboosting.
It is not just the twin dumps that cause this, it seems to happen almost at random. my exhaust was just a crappy 2.5" downpipe with 3 " system completely home made thing. Mates was Scoobysport downpipe, another was Mongoose. Dont blame the exhaust.

 

Stevie, the Blitz SBC boost controller has it's own solenoid but controls the same wastegate ..... so why should the boost control work correctly with the Blitz SBC and not with a pneumatic valve ?????, also if you left the wastegate completely open (no rod attached) and still experienced overboost then even if you re-installed the Blitz SBC, the wastegate will not be upto the job.
Could it be that after some time/use carbon starts building up on the wastegate hole decreasing it's diameter ??????

BTW do the larger IHI/Garret hybrids have a larger/ported wastegate, to avoid this problem ?????

Carlos H.

 

I think your wastegate is broken...
Are you sure it's not stuck partly open? That might explain your very low boost at 4000rpm, and the boost building uncontrollably at higher revs.

 

Had an JDM STI 7 with full decat system (HKS backbox and centre section, Apexi downpipe, custom uppipe and Cusco exhaust manifold). Noticed boost spikes up to 1.5bar on 4th gear after 4.000rpm. Cured the problem by installing an EBC (Blitz SBC DC). No boost spikes. The only problem is that the car starts detting at 1.3bar, but that's on sh***y 98RON that we have here in Russia.
Looks like a simple EBC can coupe with boost spikes if you're running above 1.0bar boost pressure. Didn't try setting the boost to <1.0bar.

Hope that helps

Nick

 

I'm sorry to say this again, but have you tried disconnecting the actuator, to wastegate arm.

Or shimming the actuator bracket to reduce the pre-load.

The actuator pre-load, and ecu boost control will be set up to spool the turbo, taking into account the restrictive, catted exhaust.

Just for reference, the P20 exhaust housing uses a 25mm wastegate.

Mark.

 

I don't think this is a D/P design issue. If it were, all the tuned cars running a twin dump d/p, would suffer the same problem, and they don't.

I also know that it's happening with various d/p designs.

Mark.

 

Mark, don't the P20 and P18 housings have the same wastegate diameter ? ..... and also if the pre-load is reduced won't this have a negative effect on the spooling time, since the actuator is already on the low side (8psi IIRC).

Carlos H.

[Edited by carlos_hiraoka - 8/26/2002 4:08:30 PM]

 

Carlos,

I'm pretty certain they do, but I only have a standard P20/TD05 here. They both have 25mm WG's.

Mark.