GFB Deceptor Pro II (part T9507) - Manual (Page 4)

Contrary to popular belief, the spring pre-load DOES NOT need to be adjusted to suit
different boost pressure. The Deceptor Pro II 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 screw in the centre of the head is the spring adjuster. Use the supplied 5mm hex key to
make adjustments. It is easiest to do this from above the valve by removing the intake air
snorkel at the front of the engine bay, so you can reach down to adjust it.
The softest spring setting is achieved when
the top of the adjustment screw is 3mm above
the head of the valve (figure 4). 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 hear
when the valve vents
? Start the car and let it warm up. Make sure the A/C is off
? Give the engine a good hard rev. The valve should blow off, then close before the revs drop
back down to idle.
? If the valve stays open and blows off for too long, and is still open when 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 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 under certain conditions. This is
a result of the different way in which this valve operates compared to the factory unit, and is
perfectly normal and is 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
Do not be afraid to experiment with the spring pre-load adjustment, you can’t cause any
damage by doing so, and getting the setting right to suit your car can help to optimise throttle
response. What you are looking for is a setting somewhere in between too soft (which can
cause bogging, poor idle, or backfiring), and too hard (which will cause significant fluttering).
Adjusting the sPRING PRELOAD