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Old 01-16-2012, 03:22 PM   #5
Scooby Specialist
Member#: 243992
Join Date: Apr 2010
Chapter/Region: MWSOC
Location: Morton Grove, Illinois
2006 WRX TR


YES, finally!!! time to call up clark turner

only downside i can find so far of straight SD.

Any SD calculation, including COBB SD, requires an input for cylinder charge temperature, which is critical to the
determination of accurate airflow via SD. The estimation of cylinder change temperature is accomplished for COBB SD
via the IAT sensor input. Generally, when the IAT sensor is in the recommended location (post-IC), the vehicle is
moving and the driver is on the throttle, the IAT input can be a fairly reliable representation of actual cylinder charge
temp. However, when the vehicle is sitting still (or at low speeds) and the driver is off the throttle (or low throttle), or
the vehicle has been sitting with the engine off and a hot engine bay for a period of time, there is the potential for the
IAT sensor to become heat soaked. That is, the sensor now reads higher than the actual intake air temp. When SD is
active, this would cause the calculated SD airflow (as well as load) to be lower than it should be, causing the car to run
lean (and with generally more timing advance). This effect may subside after the vehicle gets moving and throttle (as
well as MAP) increases, but it will generally not be an instantaneous improvement. As such, it is critical that the
owner/driver of the car understands the specific scenarios in which a heat soaked IAT sensor can potentially occur and
to avoid putting the car under high load when these scenarios are present (and for a period shortly after). This is
another reason why a wideband o2 sensor and gauge should be installed in the car and that the driver instructed on
how to determine when fueling is incorrect.

• The owner of the car also needs to understand that practically any engine mod that impacts airflow in any way
may require a re-tune or tweaking of the VE table for cars running SD. This is important as even seemingly
minor mods that a MAF sensor-based tune would have no problem accounting for, might cause a significant
enough change in VE that there could be fueling and load issues for SD.
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Last edited by WhatTurboLag?; 01-16-2012 at 03:46 PM.
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