There may be no definitive answer but it can be stated that you won't be able to run 20+ PSI on standard internals for very long no matter how you manage to defeat the built in safety fuel cut, it will be one very expensive mistake.

What you may be able to do with care and some common sense is use a Dawes Device or such like to slightly raise boost above stock and without hitting the saftey fuel cut. There is loads of material in Drivetrain just go back a few days, there is a post by John Banks listing most of the threads on this very topic.

Harry

[Edited by HarryBoy - 2/1/2002 8:52:36 PM]

 

Hi all,

Does anyone know the safe limit of boost pressure a MY99 whilst using a simple device like a bleed valve. Unfortunatley the search isnt working at the moment so i apologise if this thread has been done before which im sure it will of been. Someone told me:

The standard pressure is 0.9 bar (with 1.0 bar peak).
Increase it up to 1.35 bar can be done easily without any serious
modifications and reliability problems.
Going behind (1.5 and more) require serious care.

Translated:

The standard pressure is 13.05 psi (with 14.50 psi peak).
Increase it up to 19.57 psi can be done easily without any serious
modifications and reliability problems.
Going behind (21.75 and more) require serious care.

According to that then, you can go nearly 20 psi without problems.....Seems alot to me....

Cheers guys

 

Yeah come on people advise us as i want to turn my boost up but a bit nervous, some say its ok some say you should not?

anyone no anything about this????

scottscooby

 

fuel cut is at about 17.5 psi,but set it at no more than 16.5 or you might get overboost while overtaking a bus

 

should add that a Dawes valve(see drivetrain)is a great bit of kit.peak and held become almost the same.also some people say that a PPP ECU is a standard ECU with the fuel cut raised 2psi.I would not remove fuel cut though.

 

You may want to take a look in Drivetrain.

There is about 6 hours of reading fun about this exact topic (including datalogging etc etc) on the last 3 pages.

 

I asked my dealer Lancaster in sevenoaks to turn the boost up on my 98 turbo---They absolutly refused to do it

 

Thanks for the replies, but we still have no definitive answer anyone else got an idea??

 

You won't get a definative answer because there isn't one. Lots of people say that around 16-17 psi is still safe, but that's for their car, not yours. You have do decide for yourself but you need to get fueling etc checked out to make a proper judgement on how far you can go, or should I say, how greedy you can get!

I'd be very surprised if you get a definative answer, the standard boost level is where it is for good reason after all.

 

Realistically the failure rate for your turbo and major engine parts will increase as you increase boost. Every part of your car will be more stressed.

Common wisdom seems to be to stick to below 17.5-18 PSI, but as pointed out you can't do this on a standard ECU because of fuel cut.

If you go higher you make a load of heat and no extra power, although you might make extra torque for a while.

There is no "right" answer to this question as anyone with any scientific or engineering background would tell you. You have to decide to weight longevity against performance.

As you go too high, I don't expect the failure rate would rise in a linear fashion, but probably much worse.

Bear in mind a PPP runs up to 17 PSI in the midrange and the engines seem to last as long as anyone would expect. I personally think my engine would easily do 100000 miles at 17-18 PSI without major worries, but that is an opinion only and I won't have the car that long!

A bleed valve is IMHO a rather primitive way to raise boost. Dawes with a bleed is much better.

Even if you don't want to go up to fuel cut, raising the held boost on a MY99/00 will require you to disconnect the wastegate solenoid as with a bleed valve or similar all you will get otherwise is an increase in peak boost not held unless you trick the MAP sensor.

The long and the short of it is there is no free lunch, but 1 PSI below your fuel cut seems sensible to most folk.

 

Thanks for all the replies. It all sounds far too tricky for me. When does the fuel cut on a Standard MY99 ECU.

 

T-uk's reply at the top gives you the answer. It is not tricky at all. I did not know what a wastegate was six months ago and now I am making electronic boost controllers. It is not rocket science I promise you!