Re: To all Charlie Smith spring users

[jbtaylor@fcg.net (Jon Taylor)]

Jeff,

     I believe you are correct on most accounts. This system bleeds off a
variable percentage initially then reaches a point where it becomes a fixed
percentage that will change in direct proportion to the amount of boost:
this is what allows the computer to "see" an overboost situation and shut
off the fuel pump.  Like I said in the original post I did this mod mainly
for the safety aspects of not permanently grounding the overboost fuel pump
shutdown.  It is my understanding that with a charlie spring and overboost
shutoff ground one should have about 200 hp (with which I would see 1.7 -
1.8 bar boost)  with the computer retarding the ignition as it was
programed to do; with the air bleed mod and only the Charlie spring  the hp
would be upped to 215-220 because of the computer being faked into allowing
greater timing advance, I could be wrong about this assumption.  If you are
getting more boost using shims or an adjustable wastegate or other, I think
that there could be problems of detonation and overheating associated with
a lean fuel condition.

    You posted a while ago that you had "obtained" some adjustable pressure
switches, I think that with these  and a bank of five aquarium valves (set
to bleed .05 bar, .1 bar, .2 bar, .3 bar & .4 bar respectively) each
connected to a 12V solenoid valve (Edmund Scientific - Phone 609.547.8880,
PN B42,533, $2.28 ea.; 1/8" nipple in and out) and in turn connected to the
NAPA vacuum check-valve you should be able obtain any amount of timing at
any particular amount of boost you choose.  This, of course, would require
you ground the fuel pump cutoff. This could act like an electro-pneumatic
timing map with as many "points" as pressure switches you have connected to
the boost  presssure.  This could get somewhat complex as some pressure
switches would have to be "shut off" as other activate and each presssure
switch would have to open anywhere between 1 and 5 bleeder solenoids
depending on the amount of pressure needed to be bled (.05 bar to 1.05 bar
in .05 bar increments).
    This is all purely theoretical and my understanding of the boost
control system is definitely not as deep as others here on the list.  It
would probably be best to try about 3 pressure switches controlling 3
solenoid activated boost bleeders.   This is all purely speculative, and
remember you asked for suggestions.


Jon Taylor
'88 TQW