GFB EX50 50mm External Wastegate (part 7001) - Manual (Page 3)

Spring Selection
The EX50 comes with a 13psi spring, and also available are 7
and 9psi springs, which can be used individually or installed
together to achieve different boost levels. Use the table
opposite to determine the combination of springs required for
your desired base boost level.
Note that this table is only a guide to help your selection – the
actual boost level achieved ultimately depends on a large
number of variables, and may differ from the base boost
pressure shown in the table.
If you are planning on having variable boost through the use of a boost controller, the range you can achieve depends on
your turbo setup. The lowest boost you can achieve is determined by the spring, and you may find that boost becomes
less stable if the difference between the peak boost and the lowest boost is significant. For example, a spring that gives
9psi could be adjusted with a boost controller to give 20psi, but it is likely that boost will not be as stable as it would be
using a 16 or 20psi spring combination.
Changing the Spring
Use a metric 4mm hex key to remove 4 of the cap screws, leaving two opposing screws in place. Care must be taken
during this next step, as the spring force that is restrained by these two screws can exceed 50kg, depending on the
springs used.
Carefully remove the remaining two screws whilst restraining the cap to prevent it popping off. It is a good idea to have
a helper during this step, or better still, use a press to restrain the cap and allow you to remove it slowly.
Change the spring/s as required, and ensure they sit into the corresponding grooves in the cap. When re-installing the
cap, you can do so in any orientation to suit your purposes. Ensure the bead of the diaphragm is sitting into the groove,
then press the cap down and fully screw in two opposing cap screws, followed by the remaining four. Ensure the
screws are nipped up tight.
Boost Control Method
There are many different ways to connect the wastegate boost ports; three of the more common methods are shown
below. Whilst it is possible to use any number of different methods that are not shown here, you should always
remember the following:
•
The lowest boost pressure possible is determined by the spring
•
The lowest possible boost pressure for a given spring combination is achieved when the full boost pressure is
applied to the lower actuator port, and none to the upper port
•
Boost pressure increases when you do one or both of the following:
o Decrease the pressure at the lower port (using a boost controller for example)
o Increase the pressure at the upper port
This is the most basic method, using a pressure hose from
a boost source (often found on the turbo outlet) connected
to the lower actuator port of the wastegate cap.
This configuration results in a boost pressure that is
dictated by the wastegate spring – you must change the
spring to alter the boost level.
The unused upper actuator port should be oriented so that
water and dirt cannot easily enter.
Base Boost
Pressure (psi)
7psi
Inner
9psi
Middle
13psi
Outer
7
•
9
•
13
•
16
• •
20
• •
22
• •
29
• • •