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Throttle response or lack of under boost

markmurfie

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I just noticed something relevant in my cal. They command a high torque number at wot to make sure it’s always demanding more than the engine can produce, which makes sense. However, at high rpm, as you reduce throttle the torque demand backs off, but you have to get to around 60% pedal for torque demand to fall below torque produced at wot. This might be contributing to the delay in torque reduction response.
The throttle body model is a feed forward model for the driver demand torque. Estimated engine torque output and driver demanded torque are in a feedback loop as to keep the movement of the driver pedal relative and prevent what you describe. At WOT this is usually disabled and work in open loop of the driver demand torque value. The engine torque(torque/load tables) and throttle body model just work together. WOT has a start and end value to give this open loop torque control a hysteresis. Usually as soon as you let off the pedal the control loop goes back to closed and if your DD torque values are way above what load to torque model and throttle body is coming up with that demand value quickly lines back up. This is adaptive driver demand. Its mainly for high altitude compensation when there is less airflow and the engines maximum torque is less. That's why WOT start/end is moved out of the way in applications that manifold peak pressure is a target controlled by a waste gate duty cycle and not entirely dependent on barometric pressure.

Most after market tunes lower the WOT start value so even more of the driver demand table is meaning less and the accelerator pedal becomes throttle body model(etc vacuum from SD), torque model, and MAF dependent.
 

engineermike

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@markmurfie thanks for that. It so happens that my cal originally had the wot “start” at 50%. I tried raising this to 83% as many stock cals have it but I didn’t like the feel (too on/off), so I lowered it to 70%. I think this combined with reducing the wot torque demand at 60-100% pedal helped my backout torque reduction delay.
 

Grimreaper

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it seems the bandaid is to boot the DD vs tune it.

cant you tune DD using EBT?
lower the WOT start/stop to 50%, log what the respective pedal % provides for EBT at say 60 or 70% and then 100%, then repopulate DD with a bit if head room on those ranges but based on what the ecu things EBT is. at that point cant the wot start/stop be raised closer to stock to allow the feedforward loop to be used again?

it sounds like the issue is being able to pedal it a bit, not just left off completely.
 

Plimmer

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The throttle body model is a feed forward model for the driver demand torque. Estimated engine torque output and driver demanded torque are in a feedback loop as to keep the movement of the driver pedal relative and prevent what you describe. At WOT this is usually disabled and work in open loop of the driver demand torque value. The engine torque(torque/load tables) and throttle body model just work together. WOT has a start and end value to give this open loop torque control a hysteresis. Usually as soon as you let off the pedal the control loop goes back to closed and if your DD torque values are way above what load to torque model and throttle body is coming up with that demand value quickly lines back up. This is adaptive driver demand. Its mainly for high altitude compensation when there is less airflow and the engines maximum torque is less. That's why WOT start/end is moved out of the way in applications that manifold peak pressure is a target controlled by a waste gate duty cycle and not entirely dependent on barometric pressure.

Most after market tunes lower the WOT start value so even more of the driver demand table is meaning less and the accelerator pedal becomes throttle body model(etc vacuum from SD), torque model, and MAF dependent.
I got lazy and made all my “Borderline” timing tables 4degrees less than my “MBT” tables. Seems to work well with no noticeable lag on shifts and pedaling.
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