Using the in-car controller – GFB Deceptor Pro II Blow-off Valve (part T9503) User Manual
Page 5
The softest spring setting is achieved when the top of the adjustment screw is 3mm above the head of the valve (figure
6). Do not set the screw more than 3mm above the head (an o-ring fitted to the screw head will become visible if the
screw is wound out more than 3mm – the o-ring must remain below the head of the valve).
Set the spring to the softest setting, and set the volume control 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
Look at the piston through the trumpet. If it is hovering open, wind the adjustment screw in the “+” direction
until the piston closes fully. If it is already closed, proceed to the next step
Give the engine a good hard rev and snap the throttle shut quickly. The piston should lift and vent, 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). 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
If the piston stays open too long, and is not closed when the revs drop back to idle, the engine will “stumble”,
or the revs will dip below idle. 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, tighten the spring 1-2 turns
If a loud flutter is heard when lifting off sharply from full boost, 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
A video example of setting up the spring pre-load can be seen at:
NOTE: There is usually a range of around 4-5 turns within which your valve will operate properly, and if it is outside
this range it will be immediately noticeable in the symptoms described above. If you notice none of the symptoms
mentioned above, then simply leave it where it is.
Using the In-Car Controller
When powered up the volume dial rim will glow red, and will brighten for easy reading when you make an
adjustment, then automatically dim 3 seconds later to reduce unnecessary glare. The position of the dial is directly
proportional the venting bias - turning the dial fully anti-clockwise sets the valve to 100% recirc, fully clockwise
results in 100% atmosphere venting, and any proportion is possible between these limits.
The controller also features a program button on the rear of the casing. This can be used to limit the range of the
atmosphere-venting bias of the Deceptor Pro II. For example, if you prefer that the maximum atmosphere venting bias
is 50%, you can program the controller so that full travel on the dial gives you only 50% movement at the valve. This
is particularly useful on cars that through experimentation, find that full atmosphere venting does not agree with them.
To use this feature, set the dial in a position that you want as your maximum atmosphere-venting limit, then press and
hold the program button until the dial flashes. The unit will now record this position as the maximum atmosphere-
venting limit. Now when you turn the dial fully clockwise, the Deceptor Pro II will only open as far as the point
which you have just set. For example, if you pushed the button with the dial set in the middle (50% atmosphere
venting), full travel of the dial will now move the valve from full recirc to 50% atmosphere-venting only.
Every time the button is pushed, the position of the dial will determine the maximum venting bias of your Deceptor
Pro. So to re-set the controller to allow the full range again, simply turn the dial fully clockwise and push the button.