Caronte

Following a recent thread about the problem of overboost caused by the joint use of a PPP and a downpipe, I was wondering if keeping the OEM DP with cat and instead removing the UpPipe cat would be better off. And if so , does the result in terms of power delivery would be similar?

THX

Caronte

haynesaj

Yeah, this is what I'm interested to know too. Apparently a lot of U.S. owners are doing this with good results.

john banks

The overboost just needs to be sorted it isn't a major issue and should not stop you doing the mods you want.

If you are doing the downpipe, Pete Croney also advises uppipe on MY01 PPP because of safer ignition timing.

I would have THOUGHT that the uppipe would also increase the speed of spool up and might have similar issues? Whatever, it isn't an issue if you sort it out.

Pete Croney

Thanks John, exactly as we advise.

Caronte, first I doubt there is anyone in the world who has fitted an up pipe without changing the downpipe too, especially as it has to be removed to get at the up pipe. So no one is going to have figures. Second, we have fitted more downpipes to PPP 1995-2000 cars and 2001-2002 cars. Not one of these has had a problem with boost control because of the exhaust.

I know of a handful of such cars (less than 5) that have had boost cut problems, all of which had suffered oil contamintion of the pressure sensors/solenoid and were sorted by 15 minutes cleaning.

Boost control is no less accurate on PPP cars and seems very accurate on the latest cars.

dowser

I can confirm what John is saying. I got bad boost fluctuations when changing to a decat downpipe - it was a Scoobysport one, but I imagine any decat pipe will do it. It's not a problem with the pipe, just the crap OE boost control system not being able to react quick enough (imho).

Most noticeable in cold weather - I fitted my d/p in spring last year, and it didn't bother me much until things started getting cooler in autumn.

You can drive around it with a progressive right foot - but if you just WOT it, you get boost variations as the ecu plays catch up.

I should also add I've removed the induction resonator on my car, which also speeds throttle response, adding to the problem. Maybe leaving the resonator in place it wouldn't be such a problem? Certainly refitting the OE backbox tames it. I guess anything that slows spool up helps....

I use larger-bore restrictors to tame it at the moment - but it's an unreliable science...Dawes next, unless someone can shout loud enough to speed up the ecu

Richard

Pieman

Pete,

I notice you say "Not one of these has had a problem with boost control because of the exhaust". Is there an implication that over-boost problems might be related to induction kits etc. rather than free-flowing exhausts? ie. 'air in' related rather than 'air out'.
If so, would you expect a DP on a PPP'd MY00 to be okay only as long as the original OE airbox was retained?

john banks

Mine overboosted with the original airbox and an induction kit just the same!

Pete Croney

Guys

I haven't seen this problem, but I have seen problems from clogged sensors.

Also, on my own 99, I once had a wild fluctuation of boost on a track day. It only happened once and this was after over 30 minutes solid lapping. Accelerating out of a corner, the boost went up to 1.5bar, down to 0.6bar, up to 1.2 bar... until it settled at 1.0bar. Most strange and I cooled down and came in afterwards. No det, no damage, but a strange occurance. I put it down to the turbo overheating and it never happened again.

Is this similar to what you have seen?

I have road tested hundreds of DP'd PPP cars and they are all perfect and huge fun to drive. Hence my thinking it may be another cause.

EvilBevel

Erm ...

Hold on.

The question was about a MY01, right ? Given that the ECU from the MY01 is about as far from an "older" car as that on a Fiat Multipla, could we try to stay on topic more or less ?

I personally heard/believe that a MY01 ECU can and will bring back boost levels to the stock levels, whatever exhaust, induction, manifold etc you throw at it.

Is this information wrong then ?

Isn't is so that, unless you start to interfere in the electronic bits, that a MY01 will adjust down/up to target boost levels *much* better than a MY99/00 (we don't even consider the older models here)?

Inquiring minds want to know.

Theo

DrEvil

From what I've seen with my '01, the ECU will try to control/adjust on overboost back to stock levels, usually misses and thus over corrects.. then within about 1000rpm corrects the boost level to what it should be (stock). This was confirmed with a dyno run, and my boost gauge on separate occassions.

Rgds, Alex

PS. running a third party decat centre section and backbox at the time and ITG panel filter. oh and Optimax..


[Edited by DrEvil - 2/6/2002 5:41:34 PM]

Pete Croney

Well said Theo, we are indeed talking 01-02 here.

Boost levels... With my full system, the car holds between 14 and 14.9psi (graphed from Select Monitor), depnding on atmospherics.

The standard car holds 12-13psi, just as the book says it should.

My car has not changed with time.

You are quite right to point out the differences with the new ECU, it is a propper unit, that has been adapted to work in the Impreza. This is obvious by the way that certain functions are labelled and by the way that there are lots of functions which aren't enabled (mostly diagnostics).

Boost on the car is rock solid with virtually no overshoot.

Nathan L

Pete

What boost would a PPP + Full decat on the MY01 produce then? Would it be similar or higher ?

Nathan..

john banks

Alex's findings suggest the new ECU controls boost similar to the old one - ie closed loop AFTER spool up? The old ECU will also attempt to stabilise boost whatever you do to it as it IS also closed loop - after a fashion.

Whatever, all I am saying is if it does overboost and the solenoid is clean then it can be easily sorted MY01 or not. From what Alex is saying it sounds like the MY01 could be susceptible as well with no closed loop control during spool up, it seems odd that Pete hasn't seen this often on any MY - my solenoid is pristine clear (and works fine with my EBC even without closed loop control) and I overboost to 20PSI on the 1.2mm restrictor with PPP and DP and need 1.35mm to cure it. I don't know if the restrictor is usually changed when PPP is installed - my car needed a 1.3mm one, and then overboosted again with a DP. All this was fixed with the right orifice and the car was consistently fun to drive - it wasn't the sort of issue that you described Pete where is just happened occasionally - it was consistent and repeatable and crap unless you sorted the orifice size.

The principles of the orifice, the solenoid and duty cycles are at least partially applicable to MY01?

Theo, at least I am now stating routinely in posts what MY I am talking about, but since Pete contributed about 95-00 PPP & DP I thought I would continue the discussion. Perhaps this required another thread, but it is on the same issue and surely pertinent to MY01 owners also? Sorry if I caused any offence or confusion I am only trying to contribute my thoughts, along with limited knowledge and a fair bit of experience at working with boost control on a MY00 PPP and not. I really hope I am not running threads off topic. Sorry again if this is so.

I am genuinely interested in Pete's thoughts on this. If I and Dowser and others are finding DP boost control issues he has not had then there needs to be some more discussion to work out what is going on I believe?

Perhaps when PPP was fitted at Prodrive (Dowser fitted his own IIRC and I got mine done at a dealer) the restrictor is changed and it is conservative enough to still not overboost with a DP? Perhaps that is why I thought my PPP was quite good as I ran higher boost than most PPPs several of which show 16 PSI on RR plots, where mine was 17+ PSI.

From what Pete says about his car holding 2 PSI more with a full system the new ECU patently is not a proper closed loop system - it has all the hallmarks of the old one to me?

[Edited by john banks - 2/6/2002 5:42:51 PM]

Caronte

The PPP involves changing the restrictor as well.

Caronte

Anyway, I thought that to make the MAP sensor read a lower pressure the restrictor should have been bigger (that is the hole smaller)

john banks

The restrictor is not in the MAP line but in the line to the wastegate diaphragm - so the larger the hole, the more air hence more opening of wastegate = less boost. (unless you put a restrictor off a bleed when the opposite is true - like some earlier models I believe?)

dowser

Sorry - perhaps my post should have specifically mentioned mine was a my00 PPP. Pete - my boost issues are also repeatable, not intermittent (& my backbox sounds great, thanks!).

Caronte

Re. the PPP including a restrictor change - are you talking my01-> only? Is this info from your dealer, or Prodrive?

I didn't get a replacement restrictor with a my00 PPP that came direct from Prodrive.

Richard

EMS

The boost in a std. MY01 is very stable!

You can fit a free flow exhaust and the boost is still the same. (or very nearly the same) The first 3 - 4 times there is a little overshoot and after that the ECU "learned" the new situation.

I measured at about 6 different cars (with very different exhaust systems!) until now and all cars gave the same reaction.

The PPP is using a smaller restrictor, because there is a limit in max. duty-cycle the ECU uses to the boost solenoid. By using a smaller restrictor this maximum is not reached anymore after increasing the boost pressure, by altering the MAP signal.

Please note: all this only for MY01 and MY02!

Mark Verhoeven.

Pieman

Perhaps Mike Wood could confirm if restictors are changed when PPP is fitted at Prodrive?

Caronte

On WRX 01 the restrictor is fitted at dealer's place.

Pete Croney

I confirm that the 01 PPP includes a restrictor change, but it is as Mark says.

The 01 PPP runs 1.2 bar and is very solid.

01 boost is interesting. In certain circumstances, it sticks at 0.6 bar for a moment and then continues climbing. Normally happens on 90%'ish TPS.

john banks

VERY PUZZLED - the boost according to Mark is very stable between exhaust setups, but Pete gets 2 PSI more with a full system.

What does that mean? Is it full closed loop or not?

Caronte

But I also find strange another issue.

When accelerating at full throttle the power delivery is smooth and constantly progressive ( except a slight increase over 4000). However when accelerating at 60-80% of throttle the car pushes and releases slightly all along the rev range, like if the boost is jumping between two different values. It's not so evident but still can be felt on the back.

I remind you I have installed a PPP on a WRX 01

dowser

Caronte - do you have a boost guage? What's it doing? Could just be you're at the wastegate open/close boost pressure at this throttle postion - sounds strange though, I'd expect the solenoid to compensate.

Ultimately, take it back to the dealer if theres a problem!

Richard

john banks

Pete I am not sure I am reading you right if not forgive me, but on MY99/00 PPP changing the downpipe (at least not Scoobysport ones) seems notorious in the presence of clean pipework for causing boost control problems although not fuel cut. When I had a Magnex DP fitted (and there may be issues with twin dump as discuseed) the spool up speed was increased and as a result the boost peaked higher and the ECU dropped the solenoid duty cycle giving an underdamped response and a very disappointing almost jerky spool up which worsened when it was cold. I gathered from Dowser that he had very similar issues. The old PPP seemed to run about 17PSI held with a downpipe, but there was very little room for a peak boost above that before the boost would fluctuate. The problem was that if you enlarged the orifice to cure the overboost, the held boost sometimes would be 16-16.5PSI which was disappointing! Eventually I cured it with a needle valve which allowed much finer control than 0.1mm with drills and the brass restrictor, and then I junked the ECU boost control with Dawes and now developing a PID controlled EBC which works best of all.

Any insights welcome Pete. I gather the old ECU uses a static duty cycle map based on TPS and RPM during spool up and then homes in on target boost after a short delay hence poor compensation for breathing mods which really need a lower duty cycle to compensate or a proper PID boost control algorithm rather than the ECU's half baked one!

[Edited by john banks - 2/5/2002 2:12:52 PM]

john banks

http://www.autospeed.com/A_1054/P_4/article.html

Theo was discussing with me a link that refers to the above - I have referenced the dyno page where is shows very little gain from a full system AT THE TOP END on a MY01 which seems to contradict UK experience, and part two suggests that there is some "unlocking" of performance parts on their MY01 by remapping. I thought the UK results on a full exhaust on a MY01 were much better than this. Interesting reading anyway.

Oh I love dynos they are so precise. Not

[Edited by john banks - 2/6/2002 7:18:57 PM]