Tuning an engine can be both frustrating, and very rewarding. Sometimes, both of these can happen at the same time.

What a lot of people don’t know is that it is no longer ultra-expensive to have the tuning tools to be able to at least run your engine in a safe and near optimal manner.

The two most important issues facing engine turner are getting the correct air/fuel ratio and ignition timing for maximum power and torque, and ensuring that the engine is not going to knock (detonate, ping, pink, rattle) while you are doing this.

There are cost effective tools now days to allow you to make informed decisions while you tune your engine. These are a knock detection device, and an air/fuel ratio (lambda) device. We will go into knock detection in a future article, but in this article we will talk about monitoring the air/fuel ratio.

Determining what air/fuel ratio (AFR) you want to run on your specific engine is way outside the scope of this article, but I will go into some general AFR values that will give you an understanding of the type of measurements you will be looking for.

Stoichiometric (Stoic) – is the chemically correct AFR if you want to burn all of the fuel in the cylinder with just the right amount of oxygen. In terms of petrol, stoic (Lambda 1.0) the AFR value is 14.7:1. At Lambda 1, there should be (theoretically) the lowest emissions possible from an engine. That being said, there are still gases that are emitted from the engine even at this “perfect” 14.7:1 AFR.

The other part of the equation is that even though this appears to be best for burning all of the fuel in the combustion chamber, it is not the best for engine power, nor is it best for engine life. At Lambda 1, most engines will more easily have detonation which can lead to engine damage, and they will not produce anywhere near their real maximum power potential.

So, what do we do?

To gain maximum power, the engine must be run richer than Lambda 1 (14.7:1 AFR). In Lambda and AFR, the lower the numbers go, the richer the mixture is.

In a naturally aspirated engine (that is one without any type of forced induction), maximum power is said to be around 12.8:1 AFR, although this number will vary depending on the type of combustion chamber and many other factors to do with the design of the engine in the intake and exhaust system. So, this number is not set in stone, but it shows you that 14.7:1 is not the AFR you want for maximum power.

In terms of lowest fuel consumption, you can run an engine leaner than 14.7:1 under very light load conditions and on overrun (where you are decelerating) without causing misfires.

Where can this be used to advantage? If you are racing and the race is 2 hours long, reducing your fuel consumption may mean you have 1 less fuel stop to make saving a huge amount of time. It also means you could carry a lighter fuel load than if you had not optimized your tuning for low fuel consumption.

There are many devices you can use to measure the AFR (Lambda) of your engine, and now days they are generally all of high quality and relatively low cost. Even if you are not actively tuning, many people like to be able to see the AFR while they are driving.