MAF meters and open-loop

[Daniel Houlton]

Jason_Leone at amat.com wrote:
>
> 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).


I've waffled back and forth on the rising rate FPR.  Seems people either
like em or hate em.  I'd prefer not to plumb in an injector or two
although I guess I should be able to do that and make it still look
somewhat clean.

I like the dual pot to modify the MAF signal a lot and will try that after
I upgrade the injectors.

>
>> <<> 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)

snip

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

Yeah I know about the simple boost controllers, but they can't *lower* your
boost.  Then can only raise and/or accellerate the rise in boost by
restricting the pressure from the compressor outlet from reaching the
wastegate actuator.  i.e.  If it takes 8 lbs of pressure to open the waste
gate, then your boost is limited to 8 lbs.  Bleed off some of the signal
though (say 2 lbs) and you'll be making 10 lbs boost before the wastegate
actuator gets it's 8 lbs and opens.

To lower my boost, I'd need to add to the boost signal.  i.e., add say 2
lbs to the actuator so that at 6 lbs boost, the actuator would see 8 lbs
and open.  A spring is the only way I know of doing this without changing
to a new actuator.


>
> 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?

Yep, it's a 10 LED display.  I'm assuming it's set up in the standard way
that each LED represents .1v and maybe buffered a little bit to give a
smoother reading.  My O2 sensor is a 3-wire.  Power, ground and signal.
The A/F meter (called Intellitronix now BTW) has 3 wires.  12v power, ground
and signal.  Power and ground come from the fuse box under the dash and the
signal I've tapped into the wiring harness where it plugs into the ECM behind
the driver's kick panel.

>
>> <<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

I've heard that, and I've also heard that it's no problem.  It really depends
on who I talk to so I don't know what to believe.  I would prefer though, not
to use pressures this high.


> 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

Yeah, but they will flow like a 31 lb/hr injector at about 67 psi.  The stock
20 lb/hr only flow 30 lb/hr at 90 psi, thus my intention of using the rising
rate FPR and slightly larger injectors to reduce how high I have to raise the
fuel pressure.

> 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

I've read that most ECM can handle a 10% change in injector flow.  That would
allow me to use 22 lb/hr no problem.  Maybe 24 lb/hr if I reduce the idle fuel
pressure from 35 psi to 28 - 30 psi.  I've also read 25 psi is about the lowest
you dare go before you loose good fuel atomization.


> 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!

This is kinda what I'm leaning towards now.  Like you, I'd prefer not to raise
fuel pressure too high, but others seem to think it's OK so i thought I'd try
it.


>
> 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.

How would I do this?  I see Kenne Bell has something to do this.  It will
provide up to 16v I think to the pump to boost flow?  Cost a couple hundred $$
though I think.  Is there a circuit diagram you know of that'll show how to
build one?


Thanks for the continued response.  I'm learning more by the hour...  :)

--Dan