KRIS

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 ??

Lee

I have heard
a) ECU drops boost as redline approaches
b) turbo cant flow enough air at high rpm

takes yer pick

Bob Rawle

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).]

johnfelstead

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

KRIS

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 ???

Sam Elassar

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.

KRIS

I didnt think it would be.......damn !

johnfelstead

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?

KRIS

.....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??