Been having a problem in getting a bypass valve to work on my setup. After messing
around with a Bosch valve and then the GFB 9301 valve, I have discovered that neither
of them will work. They are designed for turbo or centrifugal s/c applications, not for
a positive displacement s/c where the throttle is before the s/c.
There are other types of bypass valve that will work, but none of them are easy to fit
with my layout which already has the spigots welded on for the Bosch valve. So to cut a
long story short, I figured a way to use the GFB valve
I took the vacuum tank and solenoid from a TVIS engine and plumbed it up to manifold
pressure and the GFB valve. The solenoid valve allows either vacuum or boost to act on
the GFB valve, depending on whether the solenoid is energised or not.
I have programmed my ECU to switch the solenoid valve at a certain MAP reading. So
the GFB valve is open below that reading to reduce inlet temps at cruise, but closed
above to avoid any loss of boost. Backyard engineering at its best... works great EDIT:
Bit of an update on this mod for the tech heads
After a few weeks of running
with this setup I discovered a flaw. When cruising and using a little bit of boost now and
then, but never actually coming right off the throttle, the valve would not open when the
MAP dropped below my switching setpoint. The vacuum tank only held enough vacuum
for one actuation... after that it needed to be recharged by seeing overrun vacuum.
However, I had recently discovered that with my setup (throttle before s/c) the vacuum
before the s/c was stronger than the vacuum after the s/c. So by way of an experiment
I changed the plumbing to put vacuum from before the s/c on the vacuum tank. Seems to
have worked, as now I can feel that little nudge of acceleration each time the valve opens
when MAP rises past my switching point. Vacuum recharge on the fly