Of course, we may want to go further and give maximum spool speed (i.e leave the wastegate closed, or 100% bleed via the boost valve) when the engine is below say 3,000 RPM, but as engine RPM, and hence exhaust flow increases, reduce the duty to our example of 60% to keep the engine at 1 Bar (and prevent overboosting during spool up) once the exhaust flow can support it.


To enable this, first set the mode to ‘Open Loop’, and in this example we would fill the open loop table as shown below. Note that this is for our imaginary example, 60% might give 1 Bar of boost in this example, but it may give significantly more (or less) on your engine configuration. We also up the duty slightly towards the end of the RPM band, to allow for more use of the exhaust gas as the turbo leaves its efficiency band.

The open loop table also references throttle position - maybe we want more boost at WOT, but less at 50% throttle and below. We also may want less aggressive spooling when under 50% throttle. The new Open Loop table may look like the below:

Of course you can tune this table to give perfect spool rate and boost holding without any overshoot, and this ‘open loop’ control mode will once again be suitable for 99% of applications. With a switch in-line, you get the high/low boost switch effect as before, also.