Setting VNT turbo boost pressure?

just had my vnt turbo fitted and its over boosting big time.
Anyone shine me some light on how to reduce the boost? also the actuator operates by vaccum?
is there ment to be a different way of connecting the actuator up?
Thanks

What boost is it hitting?


IS the boost hitting somit like 18psi then coming down to 14psi?

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Originally Posted by Os8472

What boost is it hitting?


IS the boost hitting somit like 18psi then coming down to 14psi?

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on the dash the turbo needle goes off the clock so i back off, not tried to see what it goes up to in case i blow somthing.
how do i bring this down?

you need an actuator that is boost controlled.

you need to put a normal pressure actuator on it instead of a vacuum one, a vacuum one will keep the vanes closed. I have my original t2 actuator and it boosts to about ten psi without the bleed valve

right guys ive put a t2 actuator on and im still getting stupid boost again. i set the actuator arm as long as possible so the vans are max fully open and still getting big boost?
even with the vans fully open it seems to produce big boost?

what do you call big boost?

• What rpm is boost coming in at?
• What is the boost level you are getting?
• Is boost read @ manifold or carb top?
• Do you have an after market boost gauge plummed in? (My T2 boost’s of the OE dash gauge and I am only running 1bar manifold) which is about 18psi carb top.

Actuator
Don’t think the vacuum actuator would cause over-boosting if anything it will have the opposite effect, as they are normally only set to about 2psi ish.



I see that you have put a boost actuator on it now and having the same symptoms,

• Loosen the boost actuator rod so it has minimal pre load on it so it just slides on to the vane control mechanism, (What happens now when you drive?)

Air Leaks




I would check the vacuum pipe from the actuator to the carb has no holes in it (to eliminate I would use new vacuum hosing) causing it to bleed air out this would also create over-boosting.

• Is there an under bonnet bleed valve inline? If so close it up or even better remove it for now.

If the above is fine do the following
Vanes

• Have you tried adjusting the vane grub screw on the side of the VNT (wind it all the way in) this will open the vanes up. (See article section)

If the above is all fine and been done I would then be looking at the VNT vane position within the turbo maybe they are just 2 closed on idle and just not opening enough to create a boost limit/ restriction and need adjusting.

Remember the VNT is a very different turbo to a conventional turbo with the way it brings the boost in.

Try shortening the actuator as short as possible, before you adjust the grub screw what rpm do you get boost@?