zhastaph

History

My STi 5 has been overboosting, peaks at about 18 psi. I assume(d) this is down to the decat downpipe, so I ordered a Dawes Device to control this manually, which arrived eventually.


Problem

I've connected the Dawes and wound it in a bit (just enough so you cant blow through it). She seems to be pulling about 13 PSi, sometimes peaking to a bit more than this (13.8 PSi).

I'm pretty certain that the Dawes isn't wound in enough yet to produce this sort of pressure, I'm expecting to be working almost on the wastegate alone (8 PSi)this is corroborated by the fact that I've just wound it in another full turn and it's exactly the same.

I've got plenty of thread left to wind in yet, from the documentation I'm expecting about 15/16 PSi fully wound in before I start doing stuff like removing the lock nut or padding out the spring, so I wouldn't expect to be anywhere near 13 PSi yet.


Questions

What's the wastegate on an STi 5 rated at, my understanding is that it is about 8 PSi, so I'd expect about 8 PSi of boost, is this correct?

Can the wastegate on an STi 5 be adjusted?

Is it likely to be seized or faulty?

Is it likely to have been changed, it has a blue dot on the top of it if this helps?


Many thanks for your input.

TonyFlow

interested in replies too, as my STi 5 Type R is overboosting to over 1.55bar, and am thinking about a dawes b4 I go to the hassle of porting the wastegate!

The_Judge

Hello mate,

In theory, if the solenoid hose is disconnected and plugged, and the end of the T-piece blocked off, the only thing controlling your boost is the restrictor in the hose just before the T-piece. If you were to remove that, the max boost you should get is whatever pressure the wategate opens at (you say you think it's 8psi...)

With the Dawes, did you use the hose that came with it, or the stock hose (minus the T-piece)?

There's an adjustment that can be done to the wastegate actuator arm, but buggered if I can remember what/how. I think a clip is removed, the arm is twisted a couple of turns, and clip put back on - something like that anyway. John Banks MD is your man for that...

john banks

The STi 5s I've seen don't have adjustable actuators.

Remove the Dawes and put a straight bit of hose in its place. Make sure there are no restrictors. Then see what boost you get.

However, target boost for an STi 5 is 15.7 PSI midrange, 14.6 PSI at high RPM so if you are not going above these substantially is there a problem?

zhastaph

Not as such, and in fact I'm gonna be looking to at least 17 psi with the Dawes anyway, depending upon what my KL will allow me.

My plan is to connect the actuator direct and see what boost I get, but I'm already pretty certain it's gonna be someplace between 12 and 14 psi.

My problem is, is why is it giving this boost? If it is because that's wot's it's set to then fine, it's not a problem. However if it is because the wastegate isn't able to curtail the boost properly then it is a problem, because I'm always going to have to target a much lower boost than I really want to achieve (sorta having to 'premept' the cutoff point).

zhastaph

Hi Judge, I'm sure you post wasn't in there a minute ago

This is what I reckon it should be, does anyone know if 8 psi is right and what I should be seeing.


I've stuck a piece of norprene in there at the moment.

I see you said this on another thread. This might explain a few things if this is the case. I'm guessing winding it in would have the affect of either slowing down the speed at which the wastegate opens (cos the actuator would have further to travel), or even not allowing the wastegate to open far enough. Both of which would cause boost to overshoot where it's supposed to go to. I'll take a look at this, somewhat annoyingly the clip is on the underside of the wastegate arm on the STi, which makes it a tad fiddly

john banks

Connect direct with no T-piece and no Dawes, and no restrictor and see what you get. You are guessing until then.

If you are getting inadequate wastegate flow (boost creep) this usually happens just at high RPM).

The_Judge

Dunno what turbo is fitted to the STi 5, but my experience with MY00 TD04 is quite interesting...

I recently fitted a FCD, started using Millers to keep the Knocklink quiet, and turned the boost pressure up to ~18psi. I kept it like this for a few weeks. Sometimes it was blindingly quick, and other times, "stifled"... I'm guessing this was down to knock correction, and/or reduced ignition advance due to the stupid amounts of heat the TD04 was generating. The KL was reasonably inactive, but in 5th gear at 3.5K revs, greens and ambers. I didn't see this as a problem, seeing as the only time I'm in 5th at those revs is on a motorway, which is very rare.

However, I recently had to go to Stevenage for the company, and on the way noticed the usual activity in 5th at 3.5K revs, so pulled into a service station and turned the GBE down a twist or so. Didn't notice any loss in performance, but significantly less KL activity. When I got to Stevenage, I couldn't find a BP garage that sold Ultimate, or any Shell garage, so ended up putting Sainsbury's SUL in, with a bottle of Millers. To my surprise, no difference in KL activity on the journey back to the Midlands.

I finished that tank, then forgot the Millers at my next Ultimate fill-up, so I turned the boost down again, to about 16psi. And here's the thing - hardly any differenace in performance or KL activity. It was a consistent amount of performance every acceleration. So I'm guessing 16psi is about the best boost the TD04 can produce, without drastic measures like water injection or a FMIC - or maybe NF, which I've never been able to get to try.

So I guess the main point here is boost without ignition advance is about as useful as BHP without torque...

Leslie

I fitted ported headers,H&S up-pipe, and Power Engineering full turbo back 3" exhaust with single free flow cat in the centre pipe. This was on my MY 94 STi. The boost increased to fuel cut at about 17.5-18 psi so I fitted a Dawes to reduce the top boost to 16.2 PSI. This avoids the fuel cut and the Dawes controls the boost very precisely.

Les