Drop In Boost Pressure

[icedog13]

Excuse my "noob-i-ness" here on this topic as I am on my first scoob.

53 STi UK PPP

I have had bother with the car when sitting on the motorway around 60ish and then putting the foot flat down (5th or 6th gear); the car would feel like it initially wants to take off, but then it pulses and backs off a little - still pulls like crazy, but for that initial split second it feels like it could have given a hell of a lot more.

I fitted a Prosport boost gauge last week and I can now see what is happening - when I stick the foot flat down the gauge goes right round to 1.5 bar and the car begins to pull, the pressure then drops off to 1.2 bar (the pulse feeling I mentioned) and maintains that pressure.

I don't know if this is meant to happen???

Surely if it can maintain 1.2 bar why can it not maintain the 1.5 bar??

Someone has already told me to lash the Bailey dump valve and go back to standard. If the dump valve was passing would it not be audible?

Any help would be appreciated,

Cheers in advance,

Craig.

[trackhound]

Excuse my "noob-i-ness" here on this topic as I am on my first scoob.

53 STi UK PPP

I have had bother with the car when sitting on the motorway around 60ish and then putting the foot flat down (5th or 6th gear); the car would feel like it initially wants to take off, but then it pulses and backs off a little - still pulls like crazy, but for that initial split second it feels like it could have given a hell of a lot more.

I fitted a Prosport boost gauge last week and I can now see what is happening - when I stick the foot flat down the gauge goes right round to 1.5 bar and the car begins to pull, the pressure then drops off to 1.2 bar (the pulse feeling I mentioned) and maintains that pressure.

I don't know if this is meant to happen???

Surely if it can maintain 1.2 bar why can it not maintain the 1.5 bar??

Someone has already told me to lash the Bailey dump valve and go back to standard. If the dump valve was passing would it not be audible?

Any help would be appreciated,

Cheers in advance,

Craig.

You may find that the car was mapped by prodrive to prevent over-boost in a high load/high gear/mid range condition causing a drop off in boost target and waste gate duty cycle. I assume the boost also tapers to 1.2 bar at the redline?

Cheers

Alistair

Edited December 11, 2009 by Trackhound

[Big 'D']

I would dump the Bailey and get a Forge DV setup to suit your car mate, to put it politely the Bailey DVs are rubbish and always cause issues with sticking and leaking.

Are you still using the OEM boost control?

Cheers Iain

[dipsy]

I would stick the standard dump valve back on

[trackhound]

Excuse my "noob-i-ness" here on this topic as I am on my first scoob.

53 STi UK PPP

I have had bother with the car when sitting on the motorway around 60ish and then putting the foot flat down (5th or 6th gear); the car would feel like it initially wants to take off, but then it pulses and backs off a little - still pulls like crazy, but for that initial split second it feels like it could have given a hell of a lot more.

I fitted a Prosport boost gauge last week and I can now see what is happening - when I stick the foot flat down the gauge goes right round to 1.5 bar and the car begins to pull, the pressure then drops off to 1.2 bar (the pulse feeling I mentioned) and maintains that pressure.

I don't know if this is meant to happen???

Surely if it can maintain 1.2 bar why can it not maintain the 1.5 bar??

Someone has already told me to lash the Bailey dump valve and go back to standard. If the dump valve was passing would it not be audible?

Any help would be appreciated,

Cheers in advance,

Craig.

Craig did you get this sorted just out of curiousity?

Alistair

[icedog13]

Craig did you get this sorted just out of curiousity?

Alistair

No, not yet. Just too busy right now and I don't have a garage to work in at night. Plus it's brass ootside!

Looks like going back to the original dump valve will be the obvious option to begin with -will take it from there and see what happens.

I will post back on the outcome - thanks for the advice guys.

[colin_ross]

Without wanting to state the obvious - what boost is the car mapped to?

If it's mapped to 1.2 then the 1.5 bar is the problem not the other way around. If it's overboosting them you have to find out why.

If it is mapped to 1.5 then there could be a number of possible causes. A boost leak, wastegate or dump valve could be the problem but it would be unusual for hem to hold up to 1.5 and then quickly reduce the pressure. I'd be more inclined to look at the boost controller or solenoid as it sounds like there is a slow response to the quickly increasing boost pressure when you floor it.

[dynamix]

I presume it has been decatted.

That would cause the overboost.

[P1_Paul]

I could have a look at this for you, let me know. I'm in Dunfermline.