[Supras] Dawes and boost richness

[berniek at technicaldevelop.com]

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.