GFB Deceptor Pro II (part T9504) - Manual (Page 3)

Spring Adjustment
Contrary to popular belief, the spring pre-load DOES NOT need to be adjusted to suit different
boost levels. The valve will stay shut under full throttle conditions regardless of boost pressure or
spring pre-load.
Rather, the spring pre-load affects how easily
the valve opens when you lift the throttle, and
how long it stays open when it vents. Adjusting
the spring is a simple matter of ensuring the
valve opens enough to release the air, but not
long enough to cause idling problems. The guide
below will walk you through the steps involved.
The screw in the centre of the head is the spring
adjuster (shown opposite). Use the supplied
5mm hex key for this screw.
The softest spring setting is achieved when the top of the adjustment screw is 3mm above the head
of the valve. Do not set the screw more than 3mm above the head.

Set the spring to the softest setting, and set the venting bias (via the electronic controller) to
50% atmosphere venting so you can hear the valve vent during setup

Start the car and let it warm up to normal operating temperature. Make sure the A/C is off

Give the engine a good hard rev, and listen to the valve venting. It should blow off
immediately after closing the throttle, and should only be audible for a relatively short
duration. The harder you stab the throttle, the louder the valve will vent (note: it will only
open fully when driving, as the turbo does not generate significant boost until the engine is
under load).

If the piston stays open too long and venting continues as the revs drop back to idle, the
engine will “stumble”, or the idle will be unstable. If this happens, wind the adjustment
screw in the “+” direction one turn at a time until the engine returns smoothly to idle after
revving

For the final fine-tune, take the car for a drive. Watch the tacho as you pull up to a stop - if
the revs dip below idle and then rise again, tighten the spring another 1-2 turns

If a loud flutter is heard when lifting off sharply after accelerating hard above 3500RPM,
wind the adjustment screw in the “-“ direction one turn at a time until the noise disappears.
Note that it is common to hear a slight fluttering at low RPM, particularly if you partially
spool the turbo and lift off slowly. This is a result of the different way in which this valve
operates compared to the factory unit, and is perfectly normal and not detrimental to the
turbo. However, there should be no flutter when lifting off from full boost above 3500RPM.
A video example of setting up the spring pre-load can be seen at:
http://www.youtube.com/watch?v=iqQR5WUF9lc