To all Charlie Smith spring users

[jbtaylor@fcg.net (Jon Taylor)]

Charlie Smith Spring users:

    I've been using my Charlie Spring (no-shim) for about 9 months with the
fuel pump cut-off grounded.  I have never been very satisfied with this
because of the potential dangers in both crash and overboost scenarios.
After digesting the non-remapping ECU modifications discussed extensively
about 2 months ago on the q-list I decided that I did not want to alter the
ECU's circuitry.  About a year earlier the q-list was discussing this issue
and several listers made mention of using an in-line regulator (John S.
Mockery) but with no how-to or subsequent follow-up.
    I decided to experiment with a localized bleeding off of boost to fool
the pressure sensor into thinking it had less boost than it really did;
hopefully retaining the overboost cut-out function and maintaining the
timing at the previous full boost of an indicated 1.4 - 1.5bar.  I mocked
up a boost system with a pressure tank and a very accurate regulator
feeding a length of vacuum line of similar length and dia. to the line
feeding the ECU, at the end of which I had a VDO boost gauge.  I set the
regulator to put out about .7 bar of boost pressure (an indicated 10-11psi
on the gauge) then I put a small aquarium air regulator in-line near the
gauge and by adjusting the pressure dumped by the small regulator I could
make the gauge read whatever I wanted despite a plentiful supply of of .7
bar pressurized air.  This proved to me that it would indeed be easy to
fool the ECU's presure sensor thus having the boost I wanted with the old
timimg at proir max boost (more hp) and the safety of the overboost
cut-out.
    I then installed this small aquarium air regulator about 2" up from the
brass nipple on the ECU.  The regulator output was coupled (using a 1.5"
length of hose I cut off the ECU feeder line) with a vacuum check-valve to
preserve the system's vacuum.  It is important to keep the hose lengths
from the ECU to the regulator to the check-valve as short as possible to
minimize reaction time lag at the pressure sensor.  All fittings were
clamped with small Oetiker hose clamps.  While I adjusted the regulator I
noticed that it hisses (obviously) inside the car under boost, but when I
tucked the regulator and check-valve back under the shower cap and
installed the ECU cover it was not noticeable in the car.
    It only took about 3-4 full-boost runs to adjust the regulator to
prevent fuel pump cutout, I was able to see a steady 1.5 on the dash gauge
when the regulator was dumping just enough boost to be on the very cusp of
cutting out.  I have since backed it off so that it reads a max of 1.4 bar
where I could notice the hp difference allowed by the timing at lower
boost.  I should caution all that I run 93 octane gas in the car and I have
had no problems with detonation with this install, which I have had in
place for about a month, but I would be cautious about using lower octane
gas with high boost and the now adjustable timing.
     Total parts cost was approx. $8.00, the parts I recommend are listed
below.  Try to get the regulator listed as it is cheap and high quality (a
true needle valve - most others seemed to be either all on or all off not a
linear adjustment) and serves the dual functions of a T in the line and of
the regulator, it has a built in clamp which I dremeled off so it would fit
better although this is not necessary.  It should be available at most pet
stores with large aquarium displays.

Whisper air control valve by Second Nature (single) #56001      $3.39
NAPA vacuum check-valve #730-1347                               $3.49
Oetiker 12mm hose clamps 4 @ $.26                               $1.04

I recommend this modification to Charlie Smith spring users running with a
fuel pump ground for the safety aspects alone, with the hp increase as a
side benefit.  This modification should take less than an hour to install
and adjust and is just as easy to remove.



Jon Taylor
'88 TQW


PS - I would recommend the installation of a boost gauge to monitor the
true boost reading because this installation will alter the in-dash gauge's
boost reading, although all vacuum readings are true.