Datalogging is the keystone to high performance engine tuning.
From the factory, there is only one practical way to datalog information from the ECU; via OBDII. Unfortunately, from a tuning standpoint, OBDII is woefully inadequate at datalogging. Due to the communication overhead involved in the OBDII protocol, only a meager 3 parameters at less than 2 samples a second can be collected. There is so much lag between the collection of each parameter that they often don’t align with each other, rendering the collected data effectively useless. Furthermore, the amount of parameters that can be logged is quite sparse.
For those interested in a more technical description: The standard Volvo OBDII protocol in use for both M4.3 and M4.4 is ISO 9141-2. ISO 9141-2 is a serial, bi-directional, single wire communication protocol, meaning that communication occurs on a single wire, in two directions. On a single wire serial line, communication can only occur in one direction at a time. Therefore, both devices must be in communication on which is receiving or listening. Furthermore, each ‘packet’ of relevant information must be wrapped in a descriptor, detailing the information proceeding it.
The keystone of VAST tuning is datalogging. The base for every VAST tune is a European spec ‘R’ tune, modified at the software level with a custom datalogging routine. This datalogging routine uses the same serial line as the OBDII interface, but does away with all the unnecessary code overhead present in ISO 9141-2. The VAST datalogging routine is a single sided communication protocol with no packet descriptor. This means that information from the ECU can be sent to a logging device as quickly as the serial interface will allow, with almost zero overhead.
What this means is that any parameter inside the ECU can be datalogged at a blazing 25-30 samples a second. This allows for a complete picture of how the engine is running at all times.