[Supras] Dawes and boost richness

[Jeff Mohler]

The Lex/550 mod works, but it lives within a very wide grey-band of
incompleteness.

I would not personally do this without an S-AFC, a true wideband setup, and
the occasional sanity check with an EGT guage...plus some dyno time to tweak
it in.


It seems that every Lex/500 setup is different from another.  Vf isnt very
useful to tune against.

On 11/5/07, berniek at technicaldevelop.com <berniek at technicaldevelop.com>
wrote:
>
> Joe and group:
>
> I still need to measure Af at the diagnostic connector, and purposely went
> the 550cc-Lex route to avoid complexity and the need for tuning with a
> laptop.  Right now I will have some time this coming weekend or next to
> trim up the fuel pressure and the Lex bypass, but everything now seems
> right, just like stock, but with about twice the push in the back above
> 3000 RPM (due to 57 turbo and bigger exhaust).  Maybe I'll have time next
> summer to get into laptop S-AFC tuning, but for now, I'll live with the
> same top-end richness as Toyota built into the engine in the first place.
> Getting the engine together from scratch, installing and commissioning it
> took quite a bit of free time durign the summer to the point where it had
> begun causing spouse problems.  We live about 75 minutes from the Jersey
> shore, and had gotten into the ocean 30 minutes this past summer.  So,
> next summer will offer a bit more time.  Working in defense engineering is
> all-consuming, not the "glamor" job it was 50 years ago.
>
> Bernie
>
> > By adding the Lexus AFM you've basically added a non-adjustable S-AFC.
> > Maybe a bit of a simplification, but it's essentially the same. They are
> > both lying to the ECU about the amount of air. You happen to be
> offsetting
> > that because you have larger injectors. That makes it seem more "pure"
> of
> > a mod but it's the same thing. In order to get the best (by that I mean
> > safest and most reliable) power from the car you need to be able to tune
> > it at different points. I hope that helps a bit... I don't know if you
> > have a choice but to get into the piggy-back or standalone world. :-\
> >
> > -Joe
> >
> >> Joe:
> >>
> >>     The Dawes is a relatively simple A/F ratio indicator that works
> from
> >> the last fractional volt of output from the stock O2 sensor.  I know
> >> others using them and they have been reliable.  Before installing it I
> >> did a "propane torch" test of the sensor, described elsewhere (I can
> get
> >> the link for you) and corroborated it with bench tests with a precision
> >> voltmeter.  I don't recall the exact numbers, but the Dawes does the
> >> following using a National Semiconductor analog voltage to LED driver
> >> chip:
> >>
> >> .95 to 1V:  Excessively rich, about 9:1.  Illuminates blue LED.
> >>
> >> .90 to .95V:  Just about right, about 11:1.  Illuminates green LED.
> >>
> >> .87 to .90V:  Illuminates amber LED, leaner than 11:1.
> >>
> >> Less than .85V:  Illuminates red LED, too lean for safe operation under
> >> boost.
> >>
> >>     Dawes is now known as 3 bar racing.  Although I work in defense
> >> electronics development, I have somewhat of an aversion to adding
> >> additional electronics to the car unless it is really needed.  Right
> >> now, the car behaves like stock from a fuel mixture and other
> >> operational standpoint, but with about twice the push in the back as
> >> compared with stock (above 3000 RPM).  About the only additional
> >> electronics I will add will be a 0-30 PSIG pressure sensor, with an
> >> attenuation resistor network to make the stock gauge read about 20 PSIG
> >> full scale (not interested in the meaningless vacuum reading of the
> >> stock gauge).  It is a Sensym item bought from Digi-Key for about $30.
> >> Needs a perfboard and box to replace the stock sensor (now with
> >> attenuated output to read up to about 14 PSI on the stock gauge before
> >> pinning it).  The stock sensor will saturate at about 14 PSI.
> >>
> >>     Right now the car feels as if it will beat almost anything on the
> >> road, at least up to the end of second gear (breaks the 275/40/17
> >> Bridgestones loose at about 4K-5K RPM in second).  Mods are as follows:
> >>
> >>
> >>
> >> 550cc Greddy (ND) injectors.
> >> Walbro pump.
> >> Lexus AFM, stock screw about 1/2 way in.
> >> Free flow dry AEM air filter.
> >> 3" exhaust overall and Lipp elbow, with one high flow Random Technology
> >> cat.
> >> 57 trim CT26 turbo.
> >> Radiused inlets on 3000 pipe and turbo discharge 45 degree elbow
> casting
> >> (hard pipes to come).
> >> Dawes A/F meter (reads very rich end of stock O2 sensor, and presently
> >> indicates about 9:1 AFR at full boost.
> >> Dawes boost controller set to 15 PSI, sometimes spikes to 17 PSI for
> >> less than one second.
> >> Valve bowls cleaned up with die grinder.
> >> Valve springs shimmed to about .025" less than stock height.
> >> Cometic 2.2 mm HG (block was decked twice due to rollover on floor).
> >> ARP studs torqued to 85 lb-ft (80% of yield).
> >> Modified stock FPR (works fine) set to about 38 PSI (measured with no
> >> vacuum on spring side).
> >> '89 hard captive urethane engine mounts.
> >> Moved oil pickup 3-1/2" further back in pan.
> >> Lightly cleaned up stock exhaust manifold, and Helicoiled head tappings
> >> for exhaust studs.
> >> I can feel that the stock cams make it run out of power at about 5700
> >> RPM.  But...  They will remain in place until NJ removes the inspection
> >> station dynos, now that most cars are OBD2.
> >>
> >>
> >>         Bernie.
> >>
> >>
> >>
> >>
> >
> >
> >
>
>
>
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