GFB Mach 1 Blow-off Valve (part 1001) - Manual (Page 3)

3) Depending on the configuration you choose to set up your GFB valve (vent-to-atmosphere or plumb back), ensure the
factory recirc hose that returns vented air to the intake is either plugged, or connected to your GFB valve’s outlet – do NOT
leave it open to the atmosphere. Various sized plugs and plumb back outlets are also available if required.
4) Connect the vacuum nipple on the top of the GFB valve to the inlet manifold AFTER the throttle body (see schematic
engine diagram). For best performance, where possible keep the hose run as short as possible and ensure that there are no
other accessories connected to this hose (such as fuel pressure regulator, brake booster, boost controller or boost gauge).
If you must connect other devices or increase the length of the hose, ensure that you use tee joins and vacuum hose with and
internal diameter of at least 4mm. Small diameter tee joins/hose or too many additional devices can slow the response of the
valve, or cause erratic performance.
Adjusting the spring pre-load
Contrary to popular belief, the spring DOES NOT need to be adjusted to hold different boost levels. The valve will stay shut
regardless of boost pressure or spring pre-load as long as the vacuum hose at the top receives the same full-throttle boost
pressure as the intercooler pipes. Rather, the spring adjustment changes how easily the valve opens when you close the
throttle, and how long it stays open when it vents. It is also used to accommodate variations in manifold vacuum levels on
different cars.
When the plumb back configuration is chosen, or your car does NOT have an airflow meter, the spring adjustment is not
critical and you can adjust it to suit your own preference. If your car does have an airflow meter AND you have chosen the
vent-to-atmosphere configuration, you will need to ensure the spring is set correctly, as follows:
Start by first loosening the locknut on the vacuum nipple (see second diagram on previous page) to allow it to turn easily. Set
the spring to the softest setting by turning the vacuum nipple anti-clockwise until you feel the turning resistance release. With
the car running at normal operating temperature, watch the piston through the venting outlet (not too closely!) as you stab the
throttle sharply and then release it. The piston should lift quickly and vent as you release the throttle, then close smoothly. It
should be completely closed by the time the engine drops back to idle.
If you notice any of the following symptoms, turn the nipple clockwise one turn at a time until the problem disappears:
•
The piston is open at idle
•
The valve continues to vent too long, causing the engine to “stumble” as it returns to idle speed (the revs may drop
below idle and then come back up again, or it may “hunt” for a stable idle RPM)
•
When driving, the car stalls as you pull up to a stop
•
When driving you notice a hesitation between gears or loud/excessive backfiring from the exhaust
If when driving a significant fluttering noise is heard (at full throttle or high RPM), turn the nipple anti-clockwise a few turns.
A little flutter can sometimes occur at lower RPM under certain conditions (or certain turbo systems), this is quite normal.
Note that the venting characteristics and sound of the valve can change in the first week or so, this is because the valve is
assembled using a protective grease which can slow the movement of the piston slightly during initial use.
Troubleshooting
Problem:
The valve does not vent or blow off at all.
•
Check the vacuum hose as described in section 4. Ensure that the hose you are using is indeed a vacuum source,
putting your finger over the end of it whilst the engine is running will tell you if it is or not.
•
Check the orientation of the valve. Boost MUST enter the bottom of the valve, and dump through the side. This is
particularly important to check on Audi/VW engines, and any others that use plastic Bosch-style factory valves.
•
Move the piston by hand to ensure it is not physically jammed or damaged.
•
Set the spring to its softest setting.
Problem:
The valve is leaking boost.
There are many symptoms that are often incorrectly interpreted to be a leaking valve. The design of the valve is such that
regardless of the boost pressure, if the car is at full throttle the pressure in the manifold should be the same as the pressure in
the intercooler piping. This means there is equal and opposite pressure pushing on the piston, which effectively cancels itself
out. So unless there is less pressure reaching the top of the valve via the vacuum connection, it will NOT open under boost.
Still got problems? For a comprehensive blow-off valve ‘Troubleshooting’ guide, visit our website (www.gfb.com.au) or
contact GFB directly on +612 9534 0099 or at
[email protected] .