EMS

In the past there was a discussion if a different uppipe could cure the boost creep problems with the STi7. I can immagine that because of the small diameter of the standard uppipe, the high velocity of the exhaust gasses makes it difficult to flow through the wastegate. Did anyone tested the difference?

We have now seen a couple of STi7, ALL (!) with the boost creep problem! With completely standard exhaust it is O.K. but with downpipe and rear silencer the problem start in 6th gear above 6.000 RPM.

I would like to find a solution for this in a very short time, as I am sure engines will blow the first trip to Germany!

In my opinion it can only have two reasons, because the "older" turbo didnīt had this problem (with exactly the same exhaust system after the turbo):

- The turbo design is not good (restriction in wastegate flow compared to the efficiency of the turbine) I donīt think that is the case, as the wastegate looks 100% the same as in the VF23 and I use these for years on the older Imprezaīs.

- The uppipe is causing the problem

We tested with a more restrictive 2,5" exhaust in stead of a 3" system, the max. boost reduced a little but it was still uncontrolable rising at (very) high loads.

Mark.

EMS

Anyone?

carlos_hiraoka

Have u tried porting the WG, that may help.

chg.

EMS

Carlos,

I am looking for an "easy to do" modification. Fitting an uppipe is (much!) more easy than porting the wastegate.

Mark.

Ederijke

I'm certainly no expert, but,

If the flow through the wastegate is limited, would you not have the following options;
- restrict the diameter of the uppipe to reduce gasflow (but loose power at high revs) ?
- try to fit a bigger uppipe to reduce gas-speed ?
- can you reduce turbulence in the uppipe to smoothen airflow ?
- try to dampen out the peaks (highs and lows) in the gasflow, by trying an equal length manifold ? Maybe it's the peak flow that overload the wastegate ?
- try an external (bigger) wastegate ?

Just some thoughts.

Eric

john banks

I would say port the wastegate - even though the turbo has to come off which it doesn't to do the uppipe.

EMS

Yesterday I mapped a MY99 with VF23 and SS uppipe, the car needed quite a lot more Wastegate DC at high revs compared to cars with std. uppipe. As it seems the standard uppipe from the STi has yet a smaller diameter, I think I am going to test the uppipe first.

Mark.

GDBSTi

Mark

Interesting that this problem which I had/have is becoming more prominent.

I had my turbo(VF35) off before X- mas and the wastegate design from the inside is very poor for flow. The wastegate exit is perfectly round and is completely flush with the pipe going up to the turbine blades. Compared to a TD04 which has at least a landing for the exhaust gasses to bounce back through the wastegate. I do not have a VF23 for comparison. There was even evidence (flaking of the casting and small hairline crack)developing of extreme heat on the turbine side of the wastegate exit where the exhaust gases would have been
hitting the edge. I ported the opposite side so that the wastegate exit was not flush and exhaust gases could be more easily diverted through the wastegate.

Unfortunately have have not had a chance to test whether the porting was successful yet as I have been waiting for 8 weeks for a 5th gear selector from Japan and still have to wait another 4
weeks!!!! Another issue I have experienced earlier than others!! 5th gear is weak on the STi7.

Steve Coates of AVO Turboworld in Australia has had exactly the same problems and is porting there VF35 right now. Perhaps they have some results.

Contact him at

Steve Coates
steve@avoturbo.com
AVOturboworld
Web: http://www.avoturbo.com

carlos_hiraoka

This may be a problem of the newer IHI VF turbos, both the IHI VF35 and VF30 users when changing uppipe / downpipe have reported boost creep problems. The earlier VF 22,23,24,28 and 29 never reported such problems. Hopefully this will not only mean that the wg inside design is poor, but that the new exhaust housings are better flowing too and that this requires a little bit of porting to regain boost control.

So far there has already been a quite impresive 335hp with the usual exhaust mods using it's stock IHI VF35 (UK STi) which has the smallest P15 exhaust housing, and there is also the factory S202, the STi car based on the Spec C which makes out of the factory (using two cats) 320hp with conservative boost levels. The best I have heard before out of a STi V, VI or P1 car with it's stock VF 28 turbo (older P18 housing) ~ 320hp.

GDBSTi

Steve from AVOturboworld in Aussie had this to say about porting the wastegate on VF35:

Hi Rupert...

YES!! The porting seems to have cured the problem. No creep even at
full
throttle 6000RPM in 5th!!!

Now I have extractors, large up-pipe, open air filter and the car is
NICE!!


Regards,
Steve Coates
AVOturboworld
Web: http://www.avoturbo.com
Ph: +613 9584-4499
Fax: +613 9584-4008

Callum Ferguson

iTrader: (1)

Can anyone please post before & after pictures of the WG porting and/or some 'how to' instructions. Apologies if this is a basic question which has been answered before.
Many thanks for any help provided.
callum

EMS

I want an "easy" to do modification, beginning of next week we are going to test a different uppipe and a open neck downpipe. I will post the results.

We saw no problems in 5th gear, so it doesnīt tell the whole story that Steve Coates only tested in 5th gear. I know in some countries it is illegal to go to topspeed (or you need very long private roads ), but we saw cars with no problems except in 6th gear.

I would like the boost can be held to standard values in top gear (without going to 0% duty cycle on the boostcontrol), than you have some headroom for higher loads and lower temperatures.

@Carlos,

I do not agree that this problem also is the case for the VF30. I mapped a MY99 with VF30 and I could use maximum dutycycle from 5.500 RPM and the boost didnīt go above 1.1 bar. I heard about the same story from another guy with a VF30 on his MY98.

Mark.

dowser

Hi Mark,

I've noticed similar when d/p is decatted; 6th will see a brief climb through the mid-range (currently mapped for 1.3, will hit 1.35 in 6th - strangely though, mapped for 1.2 it also hits 1.3 ).

Let us know results of up-pipe test, will save me around 4 hours

Richard

EMS

We did some testing:

The standard uppipe is almost the same as the MY99 one, so if I knew that from the beginning I hadnīt change that one!

We fitted an uppipe and a 3" open neck DP tapering to 2,5", std. mid section and a 2,5" rear silencer. Result: dissapointing! The same problem as before! In 6th gear after 5.500 RPM the boost is rising to about 1.4 bars, then we lifted the throttle.

Conclusion: The wastegate of the turbo needs to be ported after fitting a free flow exhaust, if you donīt want the boost going to over 1.4 bars at + 6.000 RPM in 6th gear!

Mark.

dowser

Thanks Mark - I'll check it out.

Richard

JIM THEO

This is what Michael (http://www.users.bigpond.net.au/msgofast/exhaustsystems.html) answers to my question on MRT forum:

quote:
--------------------------------------------------------------------------------
Originally posted by JIM THEO

I have heard that bellmouth design downpipes are better than twin dump regarding low down torque/boost control but what about splitter on open mouth Michael?
Usually new MY STIs have the tendency to overboost badly or give boost spikes at high rpm/gears with any catless downpipe, are prone to these symptoms new WRXs?
JIM

Michael by the way do you service overseas customers, I mean if I buy a downpipe from Australia could you modify it and send it to me?

--------------------------------------------------------------------------------



You lost me here a bit, the bell or open mouth are the same thing and what i would use and fit a splitter to, the 02 sti with exhaust mods over boosts with the std boost controler without mods, a few guys have run turbo XS and the boost is rock solid or remap the OEM boost control and all good.

The reason it can over boosts with catless system is the waste gate doesn't flow enough and the valve is fully open, you can drill new hole in the lever arm closer to the pivot point to give the valve more travel, i have found some V5/6's sti like this with catless systems and this has fixed them.

ye si can ship OS, i have done many right around the world.

Michael

[Edited by JIM THEO - 1/27/2003 9:50:36 AM]