While some people find reason to moan about the relentless march of technology, those of us that are always looking for more performance cannot wait for the next improvement. This story began in the 1980s, when auto manufacturers started using oxygen sensors to provide feedback for their electronic fuel injection (EFI) systems.
When it comes to burning gasoline in an engine, there is an ideal ratio of air to fuel that results in the complete combustion of the fuel. You’ve probably heard the name before. It is the Stoichiometric Ratio and its value is 14.7:1. That is 14.7 parts of air to one part of fuel. When combustion occurs at this ratio, all of the oxygen in the air is consumed and the signal from an oxygen sensor will be at a minimum.
That’s great for car manufacturers, who are heavily interested in maximizing fuel economy and minimizing emissions, both of which are achieved by burning the fuel as completely as possible. Unfortunately, the 14.7:1 ratio is not where maximum power output occurs. For older cars, say prior to the nineties, the ideal ratio to produce maximum power is around the 12.5:1 mark. The excess of fuel acts to cool the air fuel mixture due to latent heat and heat capacity changes, if at the cost of fuel consumption and hydrocarbon emissions.
Early oxygen sensors weren’t able to discriminate across a broad range of conditions, acting like a gas gauge that shows the tank as being full, half or empty. In the past few years, wide band oxygen sensors have become available and these offer an improved detection range.
OK, so you want to know what all this has to do with non-EFI cars. Engines are just as demanding whether they are fuel injected or carbureted. The key is that getting diagnostic information to help you make needed adjustments is a lot easier with a wide band oxygen sensor and meter, such as the current hand held LM-2 Kit from Innovate Motorsports. After welding a bung (threaded port) into the exhaust system, you thread the included Bosch sensor into the exhaust, make a couple of cable connections and you’re ready to go.
Here’s a diagnostic case that was relatively simple to resolve with an Innovate product, that could have been far more challenging without. A 1967 Shelby Mustang was going through a restoration and some engine work had been done. The engine was running well, except at higher revs and especially at wide open throttle, when it would run quite roughly.
With an Innovate LM-1 attached, the air fuel ratio was monitored as the engine ran. They found air fuel ratios ranging from 13.2:1 at idle to 12.5:1 at 3000 rpm. However, when they mashed the pedal and the carburetor’s secondaries opened up, the AFR went hugely lean, into the 19+ range. Rejetting the secondaries resolved the problem without further issues.
Whether you’re running EFI or carbs, the ability to watch or even datalog your engine’s AFR is important in keeping the engine healthy and avoiding lean conditions that may damage parts. Innovate Motorsports has a range of products to help with this, along with extensive diagnostic help and additional information on their web site. Check it out!