GFB Deceptor Pro II Blow-off Valve (part T9505) - Manual (Page 4)

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 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 a little 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 significant 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- this is normal and not detrimental to the turbo
Technical Support
If you experience any issues during installation or use of your GFB Deceptor Pro II that are not
answered in these instructions, please contact the GFB tech support team on +612 9534 0099, or email
[email protected] .
This product is intended for racing use only, and it is the owner’s responsibility to be aware of the legalities of fitting this product in his or
her state/territory regarding noise, emissions and vehicle modifications.
GFB products are engineered for best performance, however incorrect use or modification of factory systems may cause damage to or reduce
the longevity of the engine/drive-train components.
GFB recommends that only qualified motor engineers fit this product. Warranty is for the period of one year from the date of purchase and
is limited only to the repair or replacement of GFB products provided they are used as intended and in accordance with all appropriate
warnings and limitations. No other warranty is expressed or implied.