I got one of these thinking that it might come in handy one day...



The pic shows the top of the servo. As I had never seen one without the sticker
on top, I was interested to see that there is a socket head screw threaded down in
the hole on top of the servo. Presumeably this is an adjustment screw used by
the factory to trim the preset boost limit for the GZE ?

Has anyone ever experimented with this screw to see what (if any) affect it has
on the boost limit ? I am aware that HKS at one time offered a reworked ABV that
was fitted with a new top to the servo and incorporated an adjustment screw. But
there does not seem to be any info on the web as to what the factory screw does.

Nor have I been able to find any technical data, cutaway drawing or diagram that
explains exactly how this valve works.. and I'd like to know what's inside

Cheers... jondee86

Wow, that would be really cool if it was an adjustment screw..... not too many GZE's running around from what I've seen, those hunting for some extra psi from the SC12 have likely optted for the ABV mod as well. If you find out any additional information please post it back up here, I'd be very curious to see. I may even be tempted to try it myself if I get my GZE setup put into my new (old) car soon!

good find jondee..

Here's the Cusco ABV I have fitted to my engine

Never did find out exactly what is inside the OEM bypass valve. Boost pressure
goes up the bent tube and sits on top of the valve disc. When it goes higher than
around 8psi the pressure on the disc overcomes the spring and boost leaks back
into the intake side of the blower.

Vacuum on the small tube poking out the side pulls the diaphragm down and opens
the valve, bypassing the blower when the engine is off boost. Easy enough to
understand :0 But how the heck the screw on the top works is a mystery !!!

The Cusco modified valve is designed to work with the ABV mod which puts boost
pressure under the diaphragm to stop it opening. The valve will still open when
there is vacuum in the manifold. Assuming that the factory spring is under the
diaphragm, the only way that the adjusting screw could have any effect is if
there is a second spring on top of the diaphragm. Then, by pressing down on
the top spring you would change the point at which the valve gets sucked open
by vacuum.

This adjustment would effect the point at which the valve closes when getting on
the throttle, so that boost comes in earlier or later. That is the best theory that
I can come up with

Cheers... jondee86