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Decreasing Boost @ High Revs....cure?

Old 14 January 2000, 09:43 AM
  #1  
KRIS
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On my UK `98 The boost seems to diminish as the revs rise. At the red line the boost has dropped to about 12 -13 psi. I have a bleed valve and peak boost is about 16.5 briefly. I understand ( i think ) why this happens but my question is....... IS an ecu re-map the only way to stop boost decreasing as revs rise ??
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Old 14 January 2000, 03:24 PM
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Lee
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I have heard
a) ECU drops boost as redline approaches
b) turbo cant flow enough air at high rpm

takes yer pick
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Old 14 January 2000, 04:34 PM
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Bob Rawle
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No, its not the only answer, you could use a separate boost controller with a fuel cut defender but you would need to make very sure that the car was not knocking and that the fueling was ok etc.
Not a very "safe" solution but can be achieved with great care.

12-13 psi is standard boost.

Bob

[This message has been edited by Bob Rawle (edited 14-01-2000).]
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Old 14 January 2000, 05:16 PM
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johnfelstead
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on most production cars, boost drops at high revs as the turbo isn't big enough to keep max boost.

It may be just that in your case, i think the earlier turbos were bigger but am no skooby expert.

on my cossie i had a hybrid T3/T04 that would provide 28PSI at 7000RPM, but that was much bigger than a standard turbo.

speak to a scoob tuning company for confirmation that this is what is happening in your case

cheers

john
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Old 14 January 2000, 06:10 PM
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KRIS
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Someone has e mailed me direct , I forget who. But the reply was quite simply a new free flowing exhaust. This would allow gases to be expelled and not `back up` in the system hence causing turbo to `slow down`. Could it be that simple ???
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Old 14 January 2000, 07:03 PM
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Sam Elassar
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NO
I have the bleed valve setup and a downpipe and the boost still drops the higher the RPM goes until 6-7000 where it reaches 12-13psi. it peakes at 16-17psi intially, holds 14-15 until 5000 and then it goes to 12-13. the only car i have heard of holding 17psi all the way was bill youngs car and he had a chip as Rob pointed.
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Old 15 January 2000, 10:33 AM
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KRIS
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I didnt think it would be.......damn !
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Old 15 January 2000, 01:43 PM
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johnfelstead
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im pretty sure its just the capacity of the turbo, as mentioned above.

the 1997 models on had a smaller turbo fitted which gave more response but would be more limiting at high revs, is yours one of these?
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Old 15 January 2000, 05:21 PM
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KRIS
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.....Yes John it is, its a `98. If it involves changing the turbo then forget it. If it can be re-mapped to fuel more therefore increase the boost at high revs then that has to be the way to go,less grief. Bob, can the possum do anything like this??
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