Re: [other] Dyno-Graph (mixture meter)

[brads@mindspring.com (Brad Sheridan)]

>has anyone had an experience using the Dyno-Graph as
>advertised pg 174 of the Dec 1997 EC? I talked to the shop
>extensively and we compared his fuel mixture monitor with others on
>the market,and his sounded by far the best. Also it's not $129.95 as
>advertised, but $99.95 USD. I need some sort of exact measurement as
>I will be adding a dry NO2 nozzle in conjunction with a full throttle
>fuel enrichment module (Autotech). I want to made sure I'm delivering
>the perfect ammout of fuel to no2, or see if I need to go with a
>'wet' NOS setup.
>
>I would also be interested to hear if anyone is using a diff brand.
>Also if anyone is interested in ordering one, you should have one if
>your car is high performance modified, maybe I can get a better price
>if I order say, 5 or 10 at once.

I built one of these for approx $10 in parts.  These things cannot be
accurate, as the signal its getting is from an standard O2 sensor, which is
about as unreliable a source of data as you can get. The sensor CAN
accurately tell you if you're richer or leaner than stoich(14.7:1 air fuel
ratio), but beyond that the data is very questionable. The sensors output
is temp dependent, but I have yet to see one of these meters correct for
temp in the circuit. the output of an O2 sensor is very nonlinear,
relatively flat on either side of stoich, with a sharp slope at stoich.
Most circuits I've seen, including some of these $100+ circuits, are
linear, meaning for 10 leds, you get an led lit up for every 0.1V output of
the sensor. Now to add to all of this, you're wanting to use to it check
your mixture while on the bottle, which would have to affect the sensor
signal. I say just read the plugs. If you want the schematic, I'll mail you
a URL to check out later. At home, I also have a URL showing O2 sensor
output graph, I can add that to the list. If you do buy a meter, please
open it up, and examine the guts. If you can trace it, I can tell you how
it works, and whether or not you're getting your moneys worth. I'd be
willing to bet the main piece there is an LM3914, a $3(at most) chip, with
a few extra resistors.

Brad


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