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Thinking Man's Engine
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http://www.dawesdevices.com/airfuelmeter.html
http://www.dawesdevices.com/indash.html

This requires splicing into the OE oxygen sensor.

FAQ from the indash one.
What are the differences between this and your standard meters?:
Nothing! Except the new display! Each indicator is mounted in its own bezel on the end of an 18" lead. This allows you to put the indicators almost wherever you want. Only a .25" hole is required to mount each indicator light. The bezels "pop" into the holes for a neat and clean installation.

What does this meter do?: This meter is designed to measure the voltage output of the oxygen sensor. The lights are color coded to values that are generally recognized as safe, where the air/fuel ratio is concerned.

Why don't you use a bargraph like everyone else?: If you don't find it difficult to count segments on a bargraph at wide open throttle, then you need to run more boost. Seriously, when I first installed a competitor's model, I found it a pretty hard to read without taking my eyes off the road. The bars were dim, small, and there was not enough color distinction between the yellow and green indicators. I wanted something easy to read, that I could mount directly in front of me, or read by color out of the corner of my eye. Plus, 70% of the bargraph is supplying useless information. It just distracts you from the important info.

I noticed that your meter only has four lights, but others have 10. Why is that?: Most ten segment air/fuel meters read from 0-1 volts, in approximately .1 volt increments. Since the gauge is only read at wide open throttle, we are primarily concerned with the last 3 segments of the 10 segment display. The other segments are just flashing annoyingly when you are not using them. If you are using the first seven segments during WOT, you're too lean, and in immediate danger of toasting the engine. Our gage shows everything below .90 volts as too lean, by illuminating a red light. So, at a glance, you know "red is bad, lift throttle". From .90 to .94v, a yellow light is illuminated, indicating that you are "in the zone". You will want to think twice about increasing boost without adding fuel. From .94 to .98v, the green light is illuminated, indicating that you are getting enough fuel and are a little on the rich side. Some people prefer to stay there and enjoy an extra margin of safety, but if you want to start increasing boost, the fuel is there. From .98 volts up, the blue light illuminates, indicating that you are very rich, and may want to consider lowering fuel delivery or raising boost for more power. So you see, the resolution is actually improved over the range where you need it most (.04 volts per light vs .1volts per light), while eliminating the distracting flashing lights that you don't use.

The indicators on our meter are calibrated to .04 v increments as shown below:

First light: Red= .78 to .90v

Second light: Yellow= .90 to .94v

Third light: Green= .94 to .98v

Fourth light: Blue= .98v and up
 
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