Hi, I have bit of a niggle with my scooby (MY97 UK Turbo - Full decat and K&N, otherwise standard)

Under normal driving, boost comes in fully at 2700ish rpm, peaks at 1.1 to 1.2 bar and settles at 0.9bar. As it should

But when the revs goes past 5000rpm, in pretty much any gear (haven't tried 5th ) I notice a drop in boost pressure, falling down to a shade above 0.7bar

So two questions really:

Firstly, is this normal or not?

And secondly, what is causing it?


From my powers of deduction I figured it's either one or a combination of the following:

ECU closing the wastegate purge solonoid valve for longer duty cycles (if so, why?),
Wastegate creep, or over-sensitive wastegate actuator
TD04 running out puff (surely not)
Leaky dump valve (although would this lower the overall boost below 5000rpm too?)
Leak somewhere else (nothing obvious upon checking, but fueling seems to be ok, so I suspect there are no leaks).

Any help is appreciated thanks

SM

 

Normal, it is mapped like that. Think of airflow rather than boost. Consider charge temperature, exhaust back pressure. Turbo sizing for midrange driveability rather than power.

 

Thanks John,

Glad it's normal then

So, a remap would probably be the best course of future action then?

 

Partly, but that eats into the safety margin that has been left by not maxxing the turbo out. So increased monitoring is the order of the day. More fussy on fuel octane etc.

 

OK then - I'm just thinking about my next course of action

I'm not too bothered about trying to get extra boost at high rpms, or big BHP. I would rather have more low down response and more mid range poke...but as you know, one mod leads to another which leads to another etc. Which would probably make a JDM Sti v4/5 a better alternative (well, that's my excuse! )

 

At some point you'd still end up looking to modify...!

 

Is this the same on newage cars, i'm seeing the same but above 6000rpm