Tuning Concepts: DSM Link Airflow
This is the first volume of a three part series that will help explain in depth the three major tuning components of your engine, via DSMLink. I will cover your basic map adjustments and what they mean, allowing you to better utilize the program.
Side Note:
Before we being, don't PM me asking questions like: "what should I log for airflow, or what percent should I use at the 250hz slider?"
These questions are up to you! There is no set answer! Every car is different, so take the knowledge and apply it.
Take the theory, and learn to tune your own car. It'll save you tons of green, and give you a sense of pride and accomplishment in the end. Take the knowledge I provide, it will help you understand what is going on with your car, and give you a better picture of the chemical reaction taking place, that produces the energy.
Okay enough preaching!
The three basic maps I will discuss in detail include Airflow, Fuel, and Timing.
This section will cover Airflow.
Airflow/ MAF Compensation:
In a previous thread I discussed Volumetric Efficiency, so if you were paying attention to that, then you will have a better understanding of what we are talking about when it comes to your car's total mass air flow. If you remember the VE section, Mass Air Flow is defined as the total volume of air entering the engine, for a given period of time under a given engine condition: (Lbs/min in relation to RPM's) Well what does this actually mean? How man pounds of air is consumed per minute of rotation of the engine (RPM) for a given volume of air.
The turbo size will determine how "fast" (CFM; cubic feet/min) and how "much" (lbs/min) can be moved at one time. In other words, CFM it is a unit for measuring the rate of flow of a gas or air volume into or out of a space at a given temperature.
A turbocharger (which I will explain turbochargers in detail in a future article, so just take my word for it, for now) is a device that compresses air above ambient pressure, (1 Bar/ 14.7 psi) and delivers it to the air intake manifold of the engine at higher pressure, resulting in a greater amount of the air entering the cylinder.
In a typical vehicle running a standard Powertrain Control Module (ECU), there is a series of electronic sensors between the path of the air from the compressor (turbo) to the intake valves. These sensors consist of nothing more than voltage and frequency signals that interchange and react to different volumes, (and densities) of air masses that flow through them. If your flowing 500cfm through a mass sensor, the sensor is going to send a certain electronic value (measured in Hz) to the ECU to determine fuel consumption, (along with a number of other values), and as the volume and flow rate of air mass changes, so will the signal.
Now to put this all together, and make use of your DSMLink engine management system!
The following is an excerpt from the DSMLink V2 manual and in now way is credited to me!
The MAF Compensation dialog provides percentage adjustments at convenient intervals to apply to the MAF frequency coming into the ECU. What might not be expected is that this table is index by MAF frequency itself. Modifications to the factory MAS will tend to affect things differently based on the airflow rate through the MAS. Slower moving air has less inertia and as a result will be more likely to change direction. When less restrictive paths become available around the center metering section of the MAS (e.g., hacking or bypass tube), slow moving air will be far more likely to take those alternate paths than will air moving somewhat faster.
The Fake MAF and Use MAP options are both closely related. When Fake MAF is selected, the signal coming from the real MAF is ignored above the entered Switch over point. Instead, a MAF signal is "simulated" by ***extrapolating*** (see explanation below) from the conditions observed at the Switch over point.
If Use MAP is selected, DSMLink will factor in the value it sees on the MDP sensor line as though it were a manifold pressure (boost) signal. On 1Gs, this feature uses the EGR temp input. This assumes, of course, that you have fed an appropriate pressure signal into the appropriate input line to the ECU. If Use Map is not selected, DSMLink just uses a hard-coded value for pressure under the assumption that your boost is holding pretty steady beyond the Switch over point.
Once the Switch over point is exceeded, the MAF sensor is completely ignored until the calculated airflow drops well below the clamp point. So as your revs and estimated airflow continue to increase, DSMLink will continue to ignore the MAF sensor. Once you've let up on the gas, the calculated airflow will drop below the clamp point and DSMLink will switch back to using the real MAF signal.
Side Note for you "caveman knuckle-draggers":
****In mathematics extrapolation is the process of constructing new data points outside a discrete set of known data points.*****
Ref: DSMLink V2 Manual
Okay, now that you have a basic idea of how you're Airflow works, and what DSMLink offers you, what do I do with it?! Well, that question, (though you wish it had an easy answer) is a bit more complicated. Every engine is different, every circumstance varies, and hell I've seen exact same setups react differently on different cars, given similar atmospheric conditions!
Your best start is to determine what kind of airflow metering device you want to, or are running. The two most popular brands right now for 1st and 2nd Gen DSM are the 2G MAS, and a 3"/3.5" GM MAS (with MAF-T). Based upon what you have and what goals you plan to set, the rest is self explanatory. You need to study the theory, and conduct practical application to your car in order to get the results you want to achieve. Happy Tuning!
Thanks for reading!
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