HomeTechnical ReviewsProduct Review: Air/Fuel Gauge with Nitrous Cutoff Switch

Product Review: Air/Fuel Gauge with Nitrous Cutoff Switch

I have been absent for a little while this winter and very busy with a winter re-build project, but enough excuses. Look what I found on the Internet for you techie kind of folks.

From the good people at DynoTune comes a little device for anyone who has ever wondered how rich or lean your motor was running, an Air/Fuel ratio meter in digital format. An Air/Fuel what you say? An Air to Fuel ratio gauge and what is that you ask? Well let me refresh you on the basic principle of the combustion chamber in your motor.

It takes both Air and Fuel in a particular combination under pressure to be ignited by a spark. At a specific time, a spark is made to cause an explosion that drives the piston in a downward fashion. This causes energy transfer to your crankshaft in the motor, which transfers to your rear wheel through your transmission allowing forward movement…in other words, POWER Baby!

That’s the long of it, now what is this A/F ratio gauge I’m talking about? The A/F gauge measures the ratio of air to fuel that is being burned in your combustion chamber, or even simpler put, how lean or rich you are. For you more technical folks, the air-fuel ratio is the weight ratio of air to fuel (gasoline) drawn into the cylinder during engine intake stroke. If you are putting too much fuel into your motor, you are in a rich situation, too little fuel and your running lean. Too little and you burn stuff up, too much and you don’t have the power you want, it smokes, it gurgles, and a host of other things that happen when you’re too rich. The optimum ratio of Air to Fuel is about 13.5 pounds of air to 1 pound fuel. At this point, we have stoiciometry or the point at which the most complete combustion takes place.

AF = (mass of Air) / (mass of Fuel)

Below is a chart in which the Air/Fuel ratio gauge measures your exhaust gases and it’s corresponding voltage signal. Notice that at 14.5:1 the chart shows you’re A/F Switch shutting off your Nitrous when it becomes too lean. I will explain the switch in just a moment.


Meter reading

 Full Throttle


 .00mv    17.0:1
 .10mv    17.0:1 
 .20mv            16.0:1
 .30mv    15.5:1
 .40mv    15.0:1
 .50mv    14.7:1
 .60mv  Dangerously lean  14.6:1
 .70mv  A/F Switch shuts off the Nitrous—Very lean  14.5:1
 .80mv  Max power (Lean) normally aspirated  14.2:1
 .87mv  Max power normally aspirated  13.5:1
 .90mv  Max power (Rich) (NOS, Blower, Turbo)  13.2:1
 1.00v  Very rich  12.5:1

This little baby requires some installation procedures, but nothing that can’t be handled by your qualified bike mechanic with a welder. Yes, I said a welder. There is an O2 (oxygen) sensor that is mounted in the tailpipe after the collector that samples the exhaust gases while the motor is running. That sensor sends it’s information to the A/F ratio gauge where it is displayed in a digital format.



Now here is the best part, if you have the optional Nitrous Cutoff switch installed, this little baby will turn off your Nitrous in the event of a lean condition before you burn your motor up. How’s that for safety. The DynoTune Nitrous Air/Fuel ratio switch is the only A/F switch available. This tiny stand alone device (you need nothing else to make it work other than your O2 sensor) is a Microprocessor controlled Air/Fuel ratio gauge with a built in switch that will shut off the nitrous system if it goes lean during a Nitrous assisted run and best of all, It will work with your existing OEM oxygen sensor!

When a Rich or Lean condition occurs, the Switch will shut down the nitrous system and flash the Red status indicator (mounted below the display) for a short period (20 seconds) to tell the Driver what has happened. The switch will reset and be ready for another run automatically.

A fuel pressure switch is nice but it just does not work well enough, a bad fuel solenoid or clogged fuel jet, and it’s all over. That pressure switch did nothing to help you.

There are only a few wires to hook up and is very simple. Typical installation takes less than 40 minutes (not counting the welding procedure). The Nitrous A/F Switch is a Round 2-1/16″, 100% billet aluminum construction, definitely show quality! Comes in black or silver bezel. This kit comes with everything you need to install.

The Switch monitors your engines Air/Fuel ratio (only when nitrous is activated) based on readings from your Oxygen sensor (o2) output in millivolts.

Vehicles with Carburetors, Fuel injection, Blowers, Turbo’s, Nitrous, and this switch is a must!

This gauge has the same dimensions as their Digital Nitrous pressure gauge and makes a perfect pair in your cockpit. Both of these items can be mounted using their new-chromed gauge brackets (also available from DynoTune) that fits under most any bolt in your triple tree area or handle bars. The gauge bracket is laser cut aluminum and them chromed to perfectly fit any of the 2 1/16” gauges and switch units from DynoTune.

DynoTune Nitrous Air/Fuel ratio Nitrous switches Perform!!!

Can You Afford Not To Run One?

Compare the following features:

  • Microprocessor controlled
  • .01 Volt Resolution
  • Light
  • 12 Volt Operation
  • Fast response
  • Super Low Current Draw
  • Show quality construction

The Air/Fuel switch works with single relay nitrous systems (most systems like NOS and NX, TNT) (Will work with A ZEX kit but you must add a throttle operated micro switch and a relay, both provided with the ZEX A/F switch).

Your oxygen sensor must be in excellent working shape, if it’s over a few years old you really should change it to assure accurate readings. Note: Progressive controllers that pulse the solenoids at a throttle position less than full cannot be utilized with the a/f nitrous switch.

O2 sensor and O2 bung for pipe sold separately.

Visit: http://www.dynotune.org For complete Product listings

Guy Caputo can be reached at GuyCaputo@buckeye-express.com

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