New for 0.2.8 (05/2025)

Extended turbo options.

engine.ini:

[HEADER]
TURBO_VERSION=1 ;0 is AC, 1 is v1 CSP

[TURBO_0]                   ; This can be used for any of the turbos
FLOW_ON_CUT=0.6             ; How much exhaust energy remains on an ignition cut (vs throttle cut). Linearly interpolated to based on cut amount (100% cut yields this flow rate).

An issue with the original KS code was how electronic throttle cuts were handled. AC treated fuel/ignition cuts in the same way as throttle body movement. That meant that on cuts for gears (and for TC), it would act as though the throttle was slammed closed, reducing exhaust flow to ~0, thus letting the the turbo unspool rapidly. In reality, the throttle stays open and there is still significant airflow on ignition cuts (or timing retardation etc, anything that cuts power and isn't the throttle), allowing the turbo to maintain RPM quite well. The net exhaust energy is of course lower, as fuel is not being burned, but the airflow does certainly not go to zero. CPHYS turbo was written to correct this behavior (in a simple, easy to use manner). In short, it stops the boost dropping large amounts on electronic gear shift cuts and TC cuts like in vanilla code, allowing for the use of more realistic lag down and up times.

New in 2019

Patch adds new options for turbo, only available with extended physics: LUT for gas pedal and spin delay.

[TURBO_0]
LAG_DN=0.985
LAG_UP=0.9965
MAX_BOOST=1.0
WASTEGATE=0.58
DISPLAY_MAX_BOOST=0.58
REFERENCE_RPM=2500
GAMMA=4
COCKPIT_ADJUSTABLE=0
EXT_GAS_CURVE=(|0=0|0.3=0|1=1|)
EXT_SPIN_DELAY=0.2

Generally, gas pedal is used as a multiplier for turbo activation. With EXT_GAS_CURVE (which could also be a file name instead of inline LUT), you can remap that multiplier value, for example, stopping turbo from activating until pedal is pressed to at least 30% of its range. Somewhat similar effect could be achieved with controller with INPUT=GAS, but LUT allows to alter value before gamma is applied. Default value (for original physics) is EXT_GAS_CURVE=(|0=0|1=1|).

As for EXT_SPIN_DELAY, it adds some sort of negative turbo pressure, extending boost range. Engine would act as naturally aspirated until turbo would spin beyond zero point. With EXT_SPIN_DELAY=1, if original turbo boost would equal 0.5, after altering, it’ll drop to 0, and would climb from there. With EXT_SPIN_DELAY=0.5, it would be 0.33. Default value (for original physics) is EXT_SPIN_DELAY=0.

Thanks to dj_amur for the suggestion of adding it.