Quote:
Originally Posted by Nixlimited
This is no doubt an important achievement for the monster HP cars out there. Technically speaking, though, is there ever a way to get stock-type resolution with a MAF that still has the same voltage range and resolution (i.e. 0-5V in .01V increments)? Seems to me that no matter what, if you are pushing more air over the same range, then every increment (e.g. .01 volt) is going to represent a larger amount of incremental airflow such that your resolution is lower between those increments, right? My guess is that this is all academic, but it's always something I have been curious about. Is speed density / MAP metering any better when you get into these high HP applications?
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The relationship between voltage and airflow is not linear. Therefore, at low air flow you can still have good resolution. These MAF sensors are calibrated to have still a good resolution at low voltage 0-3V where most of the drivability and normal driving happens. In comparison to the factory ECU, it's not much different. The compromise in the resolution is only in the upper limit of the sensor. Besides, when you are at WOT, the resolution is not as critical as long as you are not maxing out the MAF's or Load Tables.
FYI, the 370Z system has a very sophisticated logic which depends on the two MAF sensors as well as the two MAP sensors. So yes the 370Z does have two MAP sensors in addition to the two MAF sensors. One is used mainly for atmospheric pressure compensation and the other is used as a switch between VVEL engine rpm control and throttle body engine rpm control. In the event that the MAP sensor for the brake booster goes below a certain threshold, it will switch to the throttle body control to make sure that there is sufficient manifold vacuum so that the brake booster can do its job.
We're very fortunate that the 370Z has dual MAF sensors so we are not completely compromising driveability and I'll bet if you take that 1000bhp Z on a test drive and test out the driveability, you'll think it was stock. I hope that all makes sense.
For the speed density vs. MAF, MAF tuning is always more precise and accurate since we're tuning based on how many grams per second of air is going into the engine. At lower altitude, you get more air, and at high altitude you get less air. The key is to have the right MAF curve that translates the amount of air going into the engine to the ECU. With speed density/MAP tuning, it's almost impossible to do on the 370Z because the VE changes so dramatically due to VVEL.
I was able to tune the G37 via a speed density system with an F-Con Vpro, but it was more of a workaround than a true tuning solution. Really it took me almost 80hrs just to get a good starting point for the car to even run. This was back in the days when there was no UpRev option and the VQ37VHR wasn't even available to the general public yet. It was an absolute nightmare, but I had no choice and got through it. It really makes me appreciate MAF tuning so much more.