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# Baro boost compensation tables

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How we can calculate the % of compensation on wastegate duty in order to avoid overboost at sea level. We are tuning at 6000 ft, we got 18.5 psi but we want the car to have 19 psi at sea level and noto overboost. We donĀ“t know the VE at the rpm range son its a bit difficult to calculate CFM at a certain RPM to calculate difference in turbine rpm to compensate.

I don't have an advisory for proposed table values for you to use, however, I do believe that starting with barometric pressure sensor data logged relative to the incorrect boost levels should give enough insight to build a rough compensation table you can refine.

I suppose you can also devise a much nicer closed loop control strategy but I got the idea that you were using an open loop strategy? Depending on the difference in barometric pressure the PID vales may not behave well enough.

I almost forgot to ask, will the car be driven from 6000 ft to sea level in competition, or is it a case where the car has been calibrated to work at 6000ft but it will be competing in a different event at sea level? Transitioning from one level to the next might need some clever thought, while the second scenario of competing at two separate altitudes might lend itself to two separate boost calibration tables. I am not sure if the ECU you are using has this feature or not but it could be worth your while to consider it.

I hope I have explained myself well enough to help you rather than confuse you. Cheers!

Thanks for the info!

Unfortunately I don't have an easy answer for you. I'm not sure you could confidently calculate the required change in wastegate duty cycle to compensate for the change in air density - I believe it would vary from installation to installation and will depend on the turbocharger and the compressor efficiency at both air densities as effectively by maintaining the same manifold pressure at two different altitudes you're operating the turbo at two different pressure ratios.

My approach would be to add a baro sensor and then log and configure your open loop duty cycle at both your desired altitudes. You could then use the baro input as an axis on your wasetgate duty cycle table to get you closer to the boost target before any closed loop control is applied. Of course depending how good your closed loop control is, this may not be necessary. You may find the closed loop control does an adequate job without needing to modify the base duty table.