07/11/2025
It’s easy to assume that every cylinder on your engine receives the same amount of air during the intake stroke, however that’s rarely the case. Minor differences in port shapes, as well as the intake manifold design, can mean that there’s minor variations in air distribution to each cylinder in the engine. Of course if you’re supplying the same amount of fuel to each cylinder then this in turn means you’ll have different air fuel ratios across the cylinders.
While this isn’t usually a deal breaker on a street engine, as we push the boundaries and specific power levels rise, a single cylinder that’s running a little lean can be potentially dangerous.
The trouble is that when we monitor the air fuel ratio in the collector of the exhaust with a single sensor we are actually seeing the average of all the cylinders air fuel ratios. For the ultimate in per-cylinder tuning, an individual lambda sensor for each exhaust runner is preferred.
This lets you monitor the AFR of each cylinder and trim accordingly. Some ECUs can even allow individual cylinder closed loop fuel control to trim out any differences automatically.
