RACEPAK

i found this diy for an air fuel gauge, is it any good?

http://www.geocities.com/Motor...m.htm

how should i read the ratio?

RACEPAK

TTT

-Trinitron-

The actual numeric value of the ratio will not be obtainable from that guage, especially using a regular o2 sensor. That gauge will simply tell you if you are rich, stoich, or lean. If you are using a stock o2 sensor; out of the 5 volts measured, the entire guage span is less than 1 volt. Meaning: don't use it to fine tune.

RACEPAK

thanks for the answer.

sorry for the noob question but what is "stoich"?

legendboy

I made one of thoes back in the day. Not really functional but kind of neat lol. Stoich is 14.7 AFR.

beepy

stoich is an abbreviation for "stoichiometric", a chemistry term that means "balanced mixture". A stoichiometric mixture of air and fuel should theoretically produce only H2O and CO2 as byproducts. True stoich is about 14.7:1 (weight/weight ratio of air to fuel), but most engines run richer than this.

I like the diagram BTW. Unfortunately, most people here are more interested in wideband systems, and wideband gauges have summing amplifiers and other more-complicated components in them.

BTW, if you are interested in building your own WBO2 kit, the full schematics and parts list can be found here:

http://www.diy-wb.com/info.htm

Unofortunately, building the thing yourself is more expensive than buying a used one.


Modified by beepy at 11:26 PM 7/27/2004

beepy

BTW, there is a much easier, although less precise and less accurate way to do the WBO2 gauge.

If you go to the above link, and find the table of O2 sensor voltage output and AFR, then plot this in Excel, you will see that the Honda wideband produces a nearly linear voltage from 10:1 to 14.7:1 AFR (1.4 to 2.45 volts), then another different linear output from 14.7:1 and up.

it is not perfectly linear, but good enough IMO.

With this information, you can take a cheap voltage gauge and alter its "full sweep" to 3.0 volts using a series resistor, then calculate needle locations at the above voltages and make a new gauge face. You don't have to make it complicated, but precise to .25 AFR, then anything above 14:1 will just be red.

It wouldn't datalog, it would only be accurate to at most .05 AFR, but it would work, and it would be damn cheap if you already have a Honda WBO2 or can get one. (making gauge faces, even nice EL ones, is as easy as drafting and using scissors)

I think I will try it. I just need to find one of those O2 sensors.