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6.7L Cummins Air Flow Adjustment

Practical Diesel Tuning

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When outfitted with an additional turbo charger (s475 over stock) and other airflow upgrades what is the proper way to tune boost with the air flow compounded but controlled by a single vgt turbo. Pusher claims you need to adjust the scaling for the intake (this really wakes the truck back up down low) and opening the vanes earlier. How does one account for the second turbo in airflow calculations for the cummins airflow maps / vane position. Is adding more fuel throughout the entire map to compensate the airflow going to allow the vanes to operate as they should or should the ecu be looking for less vane position to help the spool of the larger turbo? not sure how to modify ecu airflow when ive physically done so or if fueling is what should be focused on.


The basics of the situation remain the same. Higher vane position still results in more boost and lower vane position generally the opposite (except at high RPM and in choke scenarios). You do not need to add any fuel to the mid-range after the intake is scaled correctly.

First, make sure the airflow you're measuring is metered correctly by the MAF. Scale the MAF to by the ratio of the cross-sectional area of the flow path. This is really the most important element for drive-ability, doing this correctly will keep the truck responsive and clean, assuming your fuel scaling is accurate.

The second big part of turbo tuning for compounds is allowing the small charger turbine section to flow as much as possible at high loads. Nothing raises EGTs and drive pressure more than having non-zero values in the high RPM/high Load section of the minimum vane position map. Make sure the small turbo vane position is zero when boost is approaching 40 (verify in data logs).

Hope this is useful,


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