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Boost control cheap!
I was finally successful (to a point) in finding more boost without
spending a mint. Don't get me wrong, I am sure that Ned's IA mods are certainly
the preferred way to go. I just wanted to see what I could do without IA first.
I also can't justify $799.00 to my wife just yet.
I installed a pressure regulator between the intake and the topside of
the wastegate, eliminating the boost control solenoid entirely (more on that
later.) I bought a Wilkerson 0-30 psi pressure regulator (self-relieving) from
Fauver Company thinking that it would have an appropriate range for boost
control. The idea here is that the regulator can be adjusted to provide, for
example, 8 psi as a maximum, to the top of the wastegate. Since the bottom of
the wastegate has a supply of intake pressure, if the intake pressure rises
above (8psi + spring pressure) then the wastegate will open. The regulator will
allow any pressure in the intake, but since the wastegate will open when the
boost reaches ~8psi, then we have effective boost control.
In practise, I found that the regulator could not cope with such a low
pressure supply. It is designed for a 70-100psi supply from an air compressor.
To fix this, I dismantled the regulator, and bought a weaker spring than the
stock one. Its range is probably 0-20psi now, but it handles the low pressure
supply very well now. I can dial in any boost from 0-8.5 psi (which is where I
have it set now.) I haven't gone any higher than 8.5 since I haven't figured
out how to deal with the fuel cutoff. I think that I will be able, also, to
install the regulator in the cockpit, allowing boost control from the driver's
My next step is to put the solenoid back into the loop and see if the
computer will allow the higher boost at all. If I can make that work, then I
will have the stock safety measures back in place.
Realistically, this produces pretty good power, and is certianly adequate
for a family hauler. I'll continue tweeking however, since there is _never_
enough power <VBG> I want to get a compressor bypass valve next. I'll go see
my friend the Mazda dealer about that MX-6/Probe piece.
Graydon D. Stuckey