MAF meters and open-loop

[Jason_Leone at amat.com]

Dan,

Looks like you had some time on your hands there. For a low buck approach, why
don't you use the dual-pot method to dial in the A/F ratio w/ oversize injectors
(or a high buck shelf part like:
http://www.splitsec.com/products/arc1/arc1ds.htm ). Or, just use the proven
Hobbs switch/cold start injector methos made famous by early A1 VW turbo kits
(Callaway, etc.). I like the former method. Run 92 pump gas, and you'll be fine.
Add an intercooler for piece of mind. Your engine has really low static
compression to start with, and I think that's saving your ass right now (after
all, you are runing 87 gas and non-intercooled w/ 7psi+ boost).

<<> 4) Try lowering your boost

I'd rather not.  I'm not sure how I could either.  It's set up do deliver
full boost pressure to the wastegate actuator.  I could restrict it for
more boost, but how would I get lower boost?  Change the actuator or
hook a spring to it to help it open the wastegate?>>

You asked how to lower boost. I'm assuming your turbo unit has an integral
wastegate, right? External? Anyway, you can do it mechanically ($$), or
electronically ($$$). The mechanical method is known as a Variablle Boost
Controller (VBC), and you can make onw from common materials and off-the-shelf
parts for about $15-$20. Tuners sell these for ~$50. Basically consists of some
pressure tubing, check valve, etc. (most parts can be purchased at any
aquarium/fish shop). The length of the hose (from wastegate to the cab)
determines response time. VBCs are prone to boost spikes though (which can make
life very bad for the engine, and your wallet). The electronic method is much
better, but WAY more expensive. I like three units in particular. The Greddy
Profec A, A'PEXi Super A-VCR, and the HKS EVC IV '98. Most employ fuzzy logic,
and uses stepper motors. VERY reliable and VERY fast response time (fuzzy logic
will know the calibrated boost curve, so it will open the wastegate prior to the
set point as the boost rises...so the actual max boost level will match your
programmed setting). Prices are between $519-$600. Ouch. A MUST for medium-high
boost applications (8psi-25psi+)!

Both of the above boost control methods are totally stand-alone. No factory ECU
involvement.

That Cyberdyne A/F gauge, that's the one w/ the LEDs going vertically (lean on
the bottom, and rich on the top), right? Are you using a 4-wire EGO? I'm asuming
the A/F gauge just runs switched power to the heater, ground to the heater
ground, a tap to the EGO output signal, a tap to the EGO common signal, and
maybe a tap to the dash light circuit? Sound right? Do you know the MV range
values (giving you Lambda scale value and A/F ratio) for every LED on the A/F
gauge?

<<Stock my engine is rated at 120 hp and it uses 4, 20 lbs/hr
injectors (at 40 psi).  I have on order a rising rate FPR from cartech.net
which I'm hoping will raise pressure enough for those brief visits to 7 or
8 lbs boost which seems to be the limit without restricting the signal to
the wastegate actuator.  BTW, this will have to hit quite a high fuel
pressure.  Like 80 psi or so for brief periods.  My fuel hoses use spring
clamps.  Should I be replacing these with a more positive worm or screw
type clamp?>>

Errr, I don't like rising rate FPRs at all. Not good. They can spike the fuel
pressure w/ dangerous levels. That Cartech unit is one of them. You have to have
a ballpark idea of your hp output to choose the correct fuel components. Other
wise, it's trial and error. 80psi system pressure is ridiculous. Way to high,
even for brief periods. It's enough to blow off you little spring hose clamps at
the injectors. I think the K.I.S.S. theory applies here. Or, go w/ a VW cold
start injector and Hobbs switch. Old school, but it works. I did the
calculations, and your factory injectors are good for about 128hp (at rated
pressure, 80% duty cycle, .50 B.S.F.C.). The 24 lb/hr ones you're considering
are only good for about 140hp (at rated pressure, 80% duty cycle, .55 turbo
B.S.F.C.). That doesn't soleve the whole fuel supply problem, but helps. The
Hitachi ECU can probably handle the change, but you'll still need more fuel at
8psi (I'm assuming the engine is making ~180hp at full boost). For 180hp, you'll
need about 31 lb/hr injectors (at rated pressure, 80% duty cycle, .55 turbo
B.S.F.C.). You could use 320 cc/min injectors and raise the fuel pressure a
couple of psi above their rated pressure. Then dial in the A/F ratio with the
dual-pot method. Viola!

Ah, but we don't know what your fuel pump is capable of. You have to measure a
baseline volumetric flow (timed) and measure the pump voltage. Measure system
fuel pressure at the rail too. Once you know all that, the calculations can be
quickly made to predict the pump flow at the new system pressure. If it's higher
than the injector needs, you in the clear. If the flow is below your needs by
5%-40%, you can simply variably increase voltage to the pump until it's output
is your target fuel delivery.

Jason
'93 SLC