I have an MY99 WRX RA. I recently fitted a boost gauge so I could keep an eye on things. Held boost is currently 14psi. The gauge calibration has been checked and is very accurate throughout the positive pressure range. The problem is, if I give it full throttle in 5th gear from low revs, the gauge rises to 19psi, falls back to 12psi then rises again to the held pressure of 14 psi right through the remainder of the rev range. Is there any way I can improve sluggish response in order to alleviate the overshoot? I was thinking of raising the boost a couple of psi in the future, ensuring fueling is sufficient of course. My worry is I may experience fuel cut with the 5psi overshoot. It seems to hang around the 19psi mark forever but in reality it's probably only about a second. Any recommendations?

Don't know about the RA or Jap specs, but a peak of 5PSI over held is dodgy. If the setup is similar to UK models the problem could be gunk in the solenoid piping which can be cleaned or the restrictor size is too small. Anyway, what you describe is an underdamped boost response. The ideal seems to be under 1 PSI peak in a UK car.

You need to get a restrictor fitted to tone the boost down a little. I had the same with MY00. The dealers should be able to do it for you. Failing that a bleed valve in line should provide a means of toning the boost down.

19 PSi is fair too high :confused: UK MY00 is around 1.1 bar, dropping to 1 bar.

Import are much less!!!

Cheers Phill C

http://www.scoobynet.co.uk/bbs/threa...threadid=56487

John/ Phill,
many thanks for your advice. Not too sure the dealer would be able to help me, the service manager almost laid an egg when he heard me coming and saw that it was a Jap import. :D :D He was out in the forecourt before I could get out of the car!
I've followed the link you supplied John and it looks like a bleed valve and Dawes controller will kill 2 birds with one stone; tone down the overshoot and give me an extra couple of psi held I'm looking for.

Do you have a contact within the UK who can supply the MBC?

Thanks again,

Alan

No. I wouldn't put a Dawes on an import - they run a lot nearer det than UK models - see Martin Stirling's P1 thread - you are also flattening the boost curve and could lean out at the top. UK cars are very different! I would only replace the restrictor with a restrictor (not a bleed) valve.

John,

You know what I mean!!! Fit a bleed valve in the same position as the restrictor, that way he can adjust it until it is right....

Some dealers are Import Friendly ;) I can tell you a few.

Cheers Phill C

I'm not sure I do know what you mean Phill. Are you referring to actually bleeding air out of this line to the atmosphere before the T-piece? The system I was using was an adjustable restrictor which bled no air at all to atmosphere. I don't know if in practice there is a difference, but a bleed valve used in addition to the restrictor already in the pipe would have no method of REDUCING peak boost surely? If used a bleed valve instead of the restrictor surely you would be losing a lot of air to atmosphere which had already been measured by the MAF sensor and lead to overfuelling? These are the reasons I went strictly for a restrictor not a bleeder to replicate the original system but adjust it more precisely. Am I missing something? (not unlikely ;) )

John,

Sorry for the confusion, I added a bleed (one way valve) and turned the it down a little, in line with the existing restrictor. I thought the one way valve was a bleed valve ? It doesn't vent to atmo though!!

Cheers Phill C

PS I'm having a blonde day ;)

I was puzzled way back several weeks over why you'd put a BLEED valve on. Bleed valves do that - they bleed to atmosphere usually through a side port. A flow control valve with only two ports does not. My amateurish knowledge of pneumatics is rapidly increasing - was talking 3/2 and 5/2 solenoid valves with MTBFs and duty cycles with the best of them at the pneumatics shop today the jargon king I am ;) 2 days ago I didn't know what 3/2 or 5/2 meant! Funny, the guy in the pneumatics shop said he'd had over 20 orders from Scooby freaks for these valves! He was getting quizzed on flat spots at 120mph and kept telling people he wasn't a mechanic but just sold pneumatics. Guys were ringing up and discussing my quoted 5.5 turns from open (or whatever it was). There are folk out there even more obsessive and anal than me! Scary!

John,

****, is that my fault ? Sorry for the wrong description, what a wanker :confused: !!!!! :(

Cheers Phill

Not at all Phill. At least I am not puzzled now and know what you are on about ;)

Ok folks, I understand what you meant with the FCV in place of the restrictor. I don't however understand why I can't raise the boost a little if my fueling is fine. From what I understand about det, particularly on turbocharged applications, it doesn't need alot to destroy a piston or big end. The car has done abot 14k miles now, and boost has probably been peaking at 19psi for a large proportion of this time. I know I must get this sorted out ASAP. Held boost is 14psi all the way to the red line. The car is run religiously on SUL+ Millers. I'm sure there are plenty out there with imports running more than 14 psi held. If it's not lean, why not?
The search isn't working and I can't find Martin's post.
I know that some UK cars fuel more than others, so why should the grey imports be any different?

Thanks for your help guys, I value your comments.

Alan

I'm no expert on imports, but given that they are mapped for 100RON fuel then you need to be running SUL + OB to get near that anyway, and always SUL for safety. Adequate richness on boost is some help towards reducing detonation. It provides cooling as well. If you up the boost too much you may fall off the efficiency map of your turbo and produce high intake temperatures and risk detonation if you go too far. The ECU will retard ignition resulting in little extra power but dubious safety.

A UK car seems to be quite happy running 20-30% extra boost - the intercooler seems to manage and the fuelling seems adeqaute to put a boost controller on.

If I had an import or P1 I would go remap every time, and if upping boost much you would benefit from a front mounted intercooler. You can't just put the boost up quite so worry free.

John,

Talking about fuel, I'm certain that my car not only runs better, but is better on fuel when I use NUL. I know that this is strange, but I'm convinced.

Cheers Phill C

You are a strange boy Phill ;) But I do believe you! When are you coming up to Ed in it? You can see how horrible a Dawes makes a car to drive also ;)

Thanks for your thoughts and comments. Are you still saying that it's ok to use a flow regulator in place of the restrictor?
I agree with you John, a remap is the ideal. However, there are problems associated with this. Say I buy a link, who would map it in the NE of Scotland? What happens when perameters change and I need a remap? I might be a little niaive in thinking it's not for me but if there is anyone out there who can persuade me otherwise I'd be delighted.
Anyway, I'm going slightly off topic with this, I might post up another topic on raising of boost level now that you've solved the overshoot problem, (I think!)

Cheers,

Alan

There is no reason why you can't use a Dawes on a 99/00 import - just that UK cars are known to overfuel whereas import cars are not... well, that's not strictly true but there have been a number of well-documented problems with STi5s of a similar vintage.

If you're going to put one on a 99/00 WRX/STi, it is a VERY good idea (i.e. essential ;) ) to get the fuelling checked first on a rolling road with a wide-band air/fuel monitor.

I think it will be a bit of an eye opener - RA gearing and a Dawes - brutal ! ;)

Thanks

Gavin

[Edited by GavinP - 12/21/2001 2:16:28 PM]

I think it would be OK to use the restrictor to turn DOWN the peak boost certainly.

Thanks Gavin, it was my intention to have this done.

John,
when you say it's ok to use a restrictor to turn down the peak boost, did you mean restrictor or 2 port flow contol valve? If you meant restrictor why can't I use an FCV? Following your logic surely it's doing the same job in reducing the peak boost.

Yeah, terminology problem. Restrictor=restrictor valve=flow control valve functionally.

Thanks for clearing that up John.

Alan