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Schrappnel Knobben Longterm Test Report
LONG TERM TEST REPORT: SCHRAPPNEL KNOBBEN_tm
Due to popular demand, (well, one guy) I wrote along term
report on my experiences with the gas fed wastegate controller /
zener diode approach to increasing max boost pressure.
In short, I summarize by saying it has proven effective,
consistant, and safe, if used as directed. I have not explored
the outer reaches of the boost regime, and have no intention of
doing so without having a knock and O2 sensor installed in the system.
I can run 15-16 psia boost (2.0-2.1) bar of boost with little
problem on 91 octane gas in my 1982 TQC. This seems quite
conserative and has no undesirable effects. Compared to the IA
approach that changes ingition timing, this approach is less
wonderful. It should give idential results to some of the lesser
tuners modifications (TAP = $400). The responce at less than 1.7 bar
is the same as stock. If you take the time to spool all the was up
beyond the stock boost, you get more torque. In my stock TQC, you can
only get it only at substantial rpm's (>3500). The power band is only
between about 3500 and 5000, but when there, it will strain your neck
it pulls so strong. The region between 5000-6000 still seems like
a waste of time, although a bit less so. I'd say 220 hp is pretty
realistic guess for peak power. It dropped 1.0 second out of my 30-70 time.
A bit abour design. The problem of overboost has been much talked
about. The zener diode/resistor approach keeps the ECU from ever
shutting down do to overboost. It is possible for a stuck wastegate
or an overambitous knob adjuster to give you more than that.
I cannot eliminate that possiblity, but I can reduce the likelyhood.
I can however keep my pressure regulator from causing the problem.
Firstly, the regulators have a push lock feature to eliminates the
chance of having the knob vibrate to a new setting. Secondly, a gas
pressure saftey valve is installed between the regulator and the
wastegate, preventing it from malfunctioning in a harmful manner.
I feel this is sufficient risk reduction to allow me to run safely.
Application of this technique to other models, (5K/200) is rather
staight forward. But it has not been done. I don't own such a car.
To do the adjustment, I run the car with the ECU lid open and a
pump attached to the pressure transducer. Then I check at what
pressure and voltage the ECU cuts out. The sizing of the resistor
and diode is done to prevent the signal from exceeding that value.
It would also be possible to do a voltage dividor network which
would move the ECU cutoff upwards. I have not implimented that
approach, yet. The advantages are that you have ECU overpressure
cutoff, yet higher boost is allowed, and the boost - ignition
advance curve is modified to more advance. I.E. the boost retard
is scaled back proportionally to the voltage divider. So at low boost,
stock timing, at stock boost you have more advance, and at max boost
you get full stock retard. This may be phase two.
In the mean time, I kitted up about 5 ov these things that are
scaled for TQC's with MAC-02's. All I need to do is ship them
to anyone interested. And maybe build the little transducer
harness circuits. If you gotta soldering iron, you can do it
yourself, (and probably do a better job). I have Stevebob, Bobbob,
and Richardbob on my list for shipping. Anyone else want one?
In case you haven't figured it out, I'm not making any money on this.
I put the kits togetherfor about $20.00 each.
The kit comes with the electircals, a regulator, guage, safety vent,
fittings, clamps, and hoses, if I am feeling generous. Most everything
is surplus, which is how I get by so cheaply. I can predial them in
for a specific boost, but you can verify the actual results on your
own car since it has a guage. Remember, above 275 hp, the TQC starts
to lean out, and you could hole a piston, so don't go crazy just cause
you got a tank full of racing gas. Gotta have a O2 sensor running to make
sure your not on the hairy edge. This applies to guys with more flow
than I have. I have not installed my S4 turbo yet, but don't think
that will make a difference, since flow isn't much above stock.
Ho Ho Ho! Santa com'n to town on turbo charged sled so be good!
paul t-