GFB Deceptor Pro II (part T9520) - 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 move the noise adjusting ring to at least 50%
atmosphere venting so you can see the piston through the trumpet

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 watch the piston - WARNING: Keep your face away
from the trumpet opening when revving the engine. View the piston from an angle away
from the blast of air. The piston should lift and vent with a “whoosh”, then close slowly and
smoothly. The harder you stab the throttle, the further the piston will open (note: it will only
open fully when driving, as the turbo does not generate boost until the engine is under load).

If the piston stays open too long, and does not close before the revs drop back to idle, the
engine will “stumble”. 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 not uncommon 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
A video example of setting up the spring pre-load can be seen at:
http://www.youtube.com/watch?v=iqQR5WUF9lc