Tuning a forced induction engine on a dyno can be a daunting task. Trying to tune an engine that will make lots of boost and a ton of power can be even more challenging. These engines tend to make so much power when they come on to the boost that they often will rip right through the RPM ranges you are trying to tune. This can be very frustrating to a novice tuner.
Here’s something that may help: disconnect the tubes that lead from the turbocharger to the intake manifold. This will prevent any boost from reaching the engine, so that you can tune it as you would a naturally aspirated engine. Just operate the dyno so that it will hold you at a constant engine speed while you adjust the load with movement of the throttle and tune all the sites as best you can.
Once you have tuned all the sites for wide-open throttle in a naturally aspirated form, you can connect the boost tubes again and begin tuning the boost sites. If you have an adjustable waste-gate or boost regulator, turn it down as low as it will go and tune the lower boost sites first and gradually work your way up.
If your turbocharger has the ability to use a compressor speed sensor you can pay attention to the speeds reached during the run to make sure you are not exceeding the manufacturer’s recommended maximums. This is rare, but it could happen and it’s worth taking a look to avoid premature turbocharger failure.
When done properly, the shape of the fuel curve under boost should closely match that of the engine while naturally aspirated. It will simply use more fuel, or higher numbers in the map. The reason for this is because the engine’s volumetric efficiency for any given engine speed is determined by the combination of cylinder head, camshaft, displacement, etc.
Some ECUs use different values to represent fuel quantities in their base fuel tables, so always be sure to follow the recommended procedure for your particular system but as a general rule of thumb, the more intake pressure you run, the more fuel the engine will consume; so the larger the numbers in your fuel tables will need to be.
Ben Strader
EFI University,
Lake Havasu City, AZ
