Quote:
Originally Posted by roy'sz
What people are not considering is the size of piping and air flow. Even though you put a bigger/better exhaust on your car, hfc's and a intake doesn't mean that your car will adjust to those parts. It will max out on its default settings because obd2 was designed to compensate for variations such as temp, altitude, timing, air flow. It has basic pre set settings that are determined by size of stock exhaust tubing, intake design, stock cat cels, etc. If you throw your parts on and don't tune it (as stated before) you aren't getting the performance (not peak hp but rather full band increase in performance) that you paid for. The pre-determined settings are going to be maxed out, which is why a tune helps because it sets new parameters for air flow issues with hfc's or temp issues with cold air intakes. Feel free to chime in if I am wrong, but that is the way that I understand how the uprev helps.
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In closed loop the ECU adjusts on the fly based on MAF and O2 sensor readings. It still reads off a target table, and initially starts at that value but then relies on feedback from sensors to make the corrections necessary to hit optimal AFR. The ECU can also log and report how far off the target it was, and how much correction it's making to hit optimal. Tuning the base table allows the ECU to not have to make as large of a correction.
How that affects performance is really up in the air. Supposedly the ECU can learn the correction factor over time, and if that's truly the case, then closed loop tuning is just a matter of driving long enough to have the ECU learn the partial load curves. In this case, tuning the target table would just speed up the process. If it's making the corrections on-the-fly every time, and not "learning", then theoretically at least, there's an associated latency to the correction which could potentially effect part throttle behavior; a tune could be used to clean all this up.
Open loop, or WOT, reads straight from the fuel table based on MAF and load values and doesn't rely on a feedback loop.
The beauty of the MAF sensor is that it alone can pretty much compensate for air temperature and density (altitude). The downside is that it's calibrated for a specific housing diameter. It calculates the flow rate over a very small area that covers the sensor itself, then extrapolates based on the known diameter of the housing to get the amount of air flow.
The O2 doesn't care what the flow rate is, only the oxygen content, and as such can pretty much sample the exhaust in any diameter, just so long as it's relatively close to the exhaust stream.