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Jobe 318
01-23-2000, 07:21 PM
What is an air/fuel mix gauge reading good for? Does it help at all with being able to tune your vehicle to the environment? I know that racers use them but for what purpose. I don't know what good one would do unless you had an adjustable fuel regulator. Any insight to the device would be great.

Lee
01-23-2000, 11:24 PM
My 1969 2002 racecar has a programable fuel injection + ignition system. I use an 02 sensor and a fuel mix gauge to monitor how the engine works. In order to get the most power I have to be a bit rich. With the gauge, I am able to know where I stand and if I should modify my injection parameters. This is a must.<p>My Hartge H2.3 also has one. This way I know if I have to adjust the fuel pressure or recalibrate the airflow meter when I make a modification to, letís say, the exhaust line.

Carter
01-24-2000, 01:14 PM
<i>: What is an air/fuel mix gauge reading good for?<p>I used to race a Honda Civic in SCCA's Improved Touring catagory. The car has a carb, not fuel injection. From my experiences.....<p>The carb mixes the fuel and air that is pulled into the engine, via the engine vacuum, to be burned. This air/fuel mixture needs to be mixed at a specific ratio....that is , a certain amount of fuel and a certain amount of air. Ideally for a street car you want a 14:1 ratio, or 14 parts of air for every one part of fuel. This ratio gives the most power with the least emmisions. Generally, more air in the mixture, say 17:1, reduces the emmisions but lowers the power of the engine. This is called a "lean" condition. Some manufacturers have been researching "lean burn" powerplants to increase miles per gallon and to reduce emmisions output. Lean situations also burn the fuel very quickly in the cylinder and you get more of a "pop" burn than a "woosh" burn. This pop burn can cause over heating, pre-combustion, and can burn pistons and valves. This is a bad thing!<p>A "rich" or "fat" condition is when you have more fuel in the air/fuel mixture. Something like 11:1 or 11 parts air to 1 part fuel. This rich mixture tends to make more power, to a point, and burns cooler, thus protecting the internal engine parts. However, with a rich condition, the emmisions go up. This is a bad thing for the general air quality, but not something we really worry about on the race track.<p>That's why a slightly rich condition is good for a race car engine. And a good way to know what your engine's air/fuel ratio is, is to install an air/fuel ratio guage. Other methods of getting this info are to read the plugs and/or to install an exhaust gas temp. meter. Basically, if the plugs are white, the mixture is lean. If the plugs are dark, the mixture is rich. If the exhaust gas temp is high, you are lean, low temps mean rich.<p>Now, your BMW's fuel injection is constantly trying to get to the 14:1 ratio. It does this automatically by receiving info from the oxygen sensor and other sensors on the car.<p>The aftermarket chips usually boost the fuel at wide open throttle to richen the mixture a bit, for more power.<p>If you want to know more about how the power vs. emmisions vs. running temps are affected by plug heat range, ignition timing, compression ratios, and fuel octane etc. e-mail me privately. I've taken enough BW here already.<p>Hope this answers your question.<p>Carter


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