Boost dropping off at 5000+rpm
#1
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Boost dropping off at 5000+rpm
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
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
Last edited by Shark Man; 16 December 2004 at 10:59 AM.
#2
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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.
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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! )
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! )
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Originally Posted by john banks
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.
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