VKL723

Just read the topic of upipipes on STi 7's and I will shortly have a WRX with SS downpipe, SS up-pipe and SS centre section along with a Prodrive WRS back box will this be OK or will I see some problems.

What is over boosting and boost spikes, could someone explain these for a technical retard (trouser @ tsl's words)

Thanks for any help

Paul

elgordano

I've seen a few articles that people with the PPP who then add the full decat get overboost problems.

Is overboost still a problem with normall ECU with full decat?

G.

BugEyed

Paul

The issues of the "uppipes" on New Age STi's are many and mainly different to those on the "standard" WRX.

Firstly though a quick answer to your quesions. "Over boosting" means different things to different people, and is used to describe many issues. Simply put, it means that the turbo is producing more boost than the target set by Subaru. Limited increases in boost do not cause a problem, but too much on the MY01+ causes the ECU to retard the ignition and overfuel reducing power. In extremes you will hit the "fuel cut" where and the ECU literally cuts the fuel to the engine for a split second (and your nose hits the windscreen). "Boost spikes" are where the turbo raises boost (say at spool up) and overshoots the target boost before dropping back towards the target.

Fitting a de-cat exhaust improves the gas flow through the engine (which is why you do it), but this allows the turbo to produce more boost. On the MY01+ "standard" WRX this is not too much of a problem as it doesn't get to the point of causing a problem. If you want to you can get back to the target by changing the restrictor or fitting a boost controller (such as a Dawes or an EBC). On the STi people are seeing the boost rise higher than they like and seeing major spikes which they are worried might cause engine problems. I suppose if I had just spent £25K+ on a new toy I too would be worried about breaking it!

A number of after-market uppipes do not fit properly as the flanges are not perfectly aligned. This, particularly with the higher exhaust temperatures in the STi, can cause problems with the gaskets burning. The uppipe on the STi is of a better design than on the "standard" WRX and contains a flexible joint which is not present on the replacement uppipes that I have seen.

With an SS downpipe, SS up-pipe and SS centre section along with a Prodrive WRS back box you will this be OK on a "standard" WRX.

Hope that helps.

Duncan

Dave T-S

Duncan

Carolyn's STi7 burnt its (replacement) up pipe lower gasket through in less than 2500 miles. This is a three layer laminated steel gasket

I know of at least one MY01 WRX that has also done this. I expect there to be more.

The theory so far appears to be warped flanges on the replacement up pipes as you say. I didn't check this out accurately on Carolyn's for the simple reason that I took it off and left it off as it was contributing to the boost spikes, and put the original back on.

The expansion joint is also there for a reason.....

BugEyed

Dave

I too know of a WRX that burnt a gasket, and it is probably not the same one you are thinking of. When I first got my uppipe, I had to send it back as the angle that the flange was welded on at was incorrect. The supplier initially wriggled saying "that I should just loosen the other exhaust manifold connections and let that take up the angle". No way - that would have just saved the problem for later. The second one I got had warped flanges, but there was enough meat on the flange for me to grind it flat. Still, not exactly quality stuff.

I think that the idea of an expansion joint in the uppipe is excellent given the temperatures involved and the amount they change and frequency at which they change.

Duncan

PS The supplier of the uppipe was not a certain firm that seems to get a lot of D T-S's money.

PPS Changing the uppipe took me about 4 hours, so it is not something I would want to do on a regular basis. Having to reject the first one meant I had to refit the standard cat one, then I had to grind the second one whilst the car was in pieces. Suffice to say I will not be using that supplier again.

slippyr4

Ok, Hijacking this thread somewhat (sorry!), what are the risks of full decatting the PPP'd MY01. I'm currently under the impression that PPP raised the fuel cut, so this shouldn't be a problem. It is OK or a no go?

VKL723

Thanks alot guys for your info.
Should have said that I also have a Blitz Induction kit and I feel that the car hits the rev limiter very quickly without me noticing it, I did have a dawes but removed it safety measures, but thinking of a Turbo XS twin soleniod boost control item, been in a old model with this and was inpressed by its ease of power, anyone used one?

Thanks
Paul

Dave T-S

Slippyr4

You need to talk to RB5Scott. He's fully decatted and PPP'd his UK300 (but a few other tweaks needed too).

Mad Dog

Would a burnt gasket explain an 'orrible smell for the first 20 min after starting a MY01 WRX with SS BB, new SS downpipe and centre decat? The downpipe gasket was a little leaky at fitting but I was assured the "exhaust paste and carbon" would fix it...........

RRH

this is quite normal. i kept checking under the bonnet for the first few miles as i thought it was on fire!

it's probably down to the WD40 (or whatever) used to release the old exhaust burning off. Also the new exhausts are not degreased so they too carry oils etc that will burn off in the first few miles.

simon

Mad Dog

I had the DP fitted three weeks ago - should it still smell????

RRH

have you checked for small barbequed (is that how you spell it) animals?

BugEyed

Mad Dog

No, it shouldn't still smell after all that time, unless you only use the car once a week. Seriously, check out the joints for leaks (or as suggested, small furry animals nesting under your bonnet).

Slippery4

You can de-cat the PPP, but you will need some form of boost control. Beware of doing this without care and experience - as you say the PPP has a form of boost clamp already fitted so you can run lots of boost without the standard safegaurds.

Duncan

Dave T-S

Mad Dog

You probably have a warped downpipe mounting flange.

The one lying in my garage is also warped (I put an engineers steel rule across it to check, but it's obvious it's warped from the carbon blowby between two stud holes).

Put it this way, it is unlikely to unwarp itself.....

Dave T-S

Mad Dog

It might be better to discuss this offline - if you want to, please email me as per my profile.

Dave

Pete Croney

There have never been any over boost problems with the WRX.

The standard set up on the STi lets you grow a beard whilst waiting for it to come onto boost. A good downpipe design will dramatically change this. As boost is generated much more quickly than the ECU is expecting it, it is slow to do anything about controlling it and it can momentarily over shoot its target. The fix is a simple adjustment to one of the restrictors that determine the rate of control. Again... this is not needed on a WRX.

This only occured on a few 97/98 UK/EU spec cars and was cured in almost all cases by cleaning out an already clogged manifold pressure sensor/wastegate solenoid. The vast majority of PPP uses had nothing but perfect running.

Not on the WRX. Incidentally, all cars after 98 have had a soft cut for overboost and not the sudden, violent cut that the early cars had.

The STi up pipe is exactly the same as the up pipe fitted to all pre 01 Imprezas. The WRX up pipe is only different, as it includes a cat. These pipes need to have an expansion joint, as they are a mixture of cast iron and mild steel. Without it, they would crack instantly. This is not the case with anealed stainless, which is a much softer/more flexible material.

Flanges should be flat, no question. Gaskets are there to take up manufacturing tolerances between flanges but there is a limit to what they can fill.

Scott added a fuel controller at PE's suggestion. I know of over 20 similar set ups, none using a fuel controller, all running perfectly and with large safety margins, at well over 280bhp.

If you get a smell after 100 miles of use then this should be checked. The smell you first get is WD40 and greasy fingerprints being burnt off.

Yes Mad Dog. If it hasn't sealed properly we will investigate and correct it as necessary.

We have noticed a problem with the 01 turbo. Subaru haven't changed the gasket shape for the turbo exit since 1992, but the housing shape of the TD04 fitted to the 01 is different. One of the bottom corners of the housing completely misses the bead on the gasket by about 2mm, the gasket effectively being too small for the turbo. There is enough flex in the downpipe flange to take this up and the heat of the pipe in use will mean that the flange takes up the new shape. This may explain why Dave has noticed his one is now warped.

In answer to the original question, the full system is fantastic and problem free on your WRX

[Edited by Pete Croney - 4/16/2002 1:34:17 PM]

RB5SCOTT

My car was running slightly lean at the top ( 6%) but i have an APS induction kit and ported headers. As Pete says a full de-cat with ITG will not run lean

Scott

BugEyed

To clarify further, 6% is not lean (it is about the limit), but if you have other things beyond a PPP and a Scoobysport fully Decat exhaust (uppipe, downpipe, mid and backbox) you might run lean. This is more due to the injectos approaching their max duty cycle.

Duncan

rich a

Thanks to Pete for responding to this as i was getting a bit twitchy cos i've just booked my uk300 ppp in for full ss system so i hope there will be no probs

Rich

Pete Croney

Duncan

There's plenty more in the injectors.

If there wasn't, the fuel controller wouldn't do anything

Mike Tuckwood

When you allow the car to breathe better, it starts to pick up faster than it has been taught/programmed to deal with.

With that in mind and to give some clarity if you imagine on a scale from 1 to 100, the acceleration rate that the car is expecting to produce boost pressure, (given the known/designed restrictions and back pressure within the exhaust system).

Then normally the car will produce boost at an acceleration rate of say 40.
The control equipment, wastegate control particularly and it's contol mechanisms are geared up for boost building at that speed.

If you free up the 'breathing' (Any/all exhaust pipes including up-pipes, headers, and induction), of the car the reduction in back pressure will allow boost to build up markedly faster to an acceleration rate of (with a full decat) say 80. (and it can be that much).

Then obviously boost can build up much faster than the control equipment has been taught to/can deal with.

This usually results in "overboost cutout" where the pre programmed safety valve (not a physical item) realises that boost is too high and puts a complete stop on everything by cutting the fuel (or ignition on some cars), at a pre-determined point (thus allowing the boost to drop immediately).

The more you 'open up' the system, the more likely you are to arrive at 'overboost' so in essence the faster you want your car to go, the more likely you are to encounter overboost by improving the breathing.

Boost peak/spike is simply the highest boost pressure level achieved.

Control methods are various depending on the type and severity of the particular problem experienced. The use of different restrictors simply allows less boost to build by allowing more (when there is more) pressure to bleed off and start to open the wastegate earlier, thus controlling the boost ramp (boost acceleration rate).

There are specific boost controllers (EBC's) which serve the sole purpose of controlling boost to levels which are 'user dictated.'

All quite simple really. I wrote this in one go, so don't be surprised to see multiple edits as I correct errors made.


Mike.

[Edited by Mike Tuckwood - 4/10/2002 10:24:22 AM]

Dave T-S

(edited as misread post)



[Edited by Dave T-S - 4/11/2002 9:04:30 AM]

Mad Dog

I've checked, no obvious furry animals / turds etc to be seen.

I use the car every day with a good couple of hours' driving.

I've also checked for oil leaks and had the dealership check for them too on its service last week - found nothing. They did, however, find that two bolts were missing from the downpipe, which they replaced.

Dave, you're starting to lose me with all this talk of warped mounting flanges. How do I check for leaks from the exhaust system?

Should I take it back to Scoobysport????

Thanks.


[Edited by Mad Dog - 4/12/2002 5:44:33 PM]