Air temperature also plays into detonation resistance too though, a hot charge won't take as much timing as a cold charge at the same AFR. I'm honestly not sure of the specifics as to how a MAF generates it's signal, and how temperature compensation takes place.pmbrunelle wrote: ↑Mon Jun 08, 2020 10:10 pm Air temperature is used in speed-density to correct for the air density variation with temperature. If you're using a MAF, you don't really need an air temperature sensor anymore, as you're taking a direct mass flow measurement.
Be careful with air temperature sensors placed after a turbocompressor. When gas is compressed, its temperature rises (immediately). This means that at the moment we hit full boost, the compressor discharge air is hot right away! When you shift and you're no longer boosting, the discharge temp goes right back down.
If you're running speed-density, this means that your temperature sensor must be fast enough to react to the temperature swings. If your sensor doesn't react fast enough, the speed-density algorithm is working off the wrong data.
I tested my open-element sensor by dunking it into a pot of boiling water. It took seconds for its resistance to stabilise after the dunk. I have about 0.3 seconds of turbo lag between WOT and full boost. So forget it, a post-compressor sensor would never keep up.
On my Fiero (which is running speed-density), I placed the temperature sensor in the intake duct just behind the intake scoop. It's basically reading the ambient air temperature. The air density reduction due to the temperature rise of the compressor ends up being baked into my VE(RPM, MAP) table. It seems to work well enough, but I usually hang around the same altitude (which happens to be near sea level). I think if I drove my car to a different altitude, the compressor would be working at a different pressure ratio for a given MAP, so the mass flow estimation would be off.
With an intercooler, temperature estimation gets complicated (since the sensors are slow), so MAF starts to sound like a good idea...
the sensor lag time is also part of the reason we tune our cars, as we can see the response of the whole system, and calibrate accordingly. I am curious about the response time of my card MAF's IAT sensor, but I'm not really sure of a way to perform a repeatable test without destroying it. I was also considering using the water discharge temperature from the intercooler to adjust timing, as there should be a linear correlation between charge temperature and water outlet, but it adds an additional variable that isn't as predictable without adding at least 1 additional water inlet temp sensor.
I don't think is objective was ultimate power, it was more of a test to show the effectiveness of the two different methods of charge cooling, power output being the factor that changes the most. I would like to see a comparison with a system more like yours, which directly supply's the mixture to each cylinder, which was the major pitfall of water/meth on an LSx like in the video, the front cylinders get the juice, and the rear run dry, which means you reach a limit on some cylinders, while you still have room to go on others. He talks about it quite a bit around the 15 minute mark. Richard does a ton of test videos and claims to tune each setup to the best achievable output that he can, while i would love to write it off as marketing, I've seen him test stuff that costs nothing, which to me, lends some credibility to his work.pmbrunelle wrote: ↑Mon Jun 08, 2020 10:10 pm Some comments on the video
The dude missed the point of the water/meth injection. Water/meth isn't a power adder on its own. What it can do is stave off detonation, which allows you to run more boost without detonation.
The video shows an air temperature reduction (in the compressed air piping) with the water/meth, as cool as with the intercooler... I'd call BS on that result. If the air temperature was the same as with the intercooler, the air density would be the same, and then the power would be the same.
However, power on water/meth was the same as with the non-intercooled non-injected configuration, so I reason that the air density (and thus temperature) was the same as with the non-intercooled non-injected configuration.
My bet is that the water/meth droplets were hitting the temperature sensor and cooling it, giving a false temperature reading!
The BOV isn't really a problem unless you install it after the MAF, pre-MAF and you don't have to recirculate it as the air is exhausted prior to the air getting to the MAF.pmbrunelle wrote: ↑Mon Jun 08, 2020 10:10 pm I think that if you can package an intercooler, it's a good thing to have. However, depending on its own temperature, it may not always cool the compressed air the same amount, which introduces another variable that can lead to inconsistency with the tune. However, if you have a MAF, the tune problem is largely solved.
The MAF is just a bit more tricky in that you have to install the MAF itself, and you have to recirculate your BOV flow. So it's more fabrication / packaging work.
pmbrunelle wrote: ↑Tue Jun 09, 2020 6:33 pmThe input capture unit of a typical microcontroller is 16-bit. (for frequency measurement)The Dark Side of Will wrote: ↑Tue Jun 09, 2020 2:15 pm GM's decision to relate MAF to frequency vs. Bosch's decision to use 0-5V definitely gave the GM sensors at least one and maybe two significant digits of precision, though.
The ADC of a typical microcontroller is typically 12-bit. (for analog voltage measurement)
The increased accuracy, from what i remember reading, was more related to the fact that by outputting a frequency instead of a voltage, resulted in the reading of the MAF not losing accuracy based on parameters related to wire length and ground resistance.
as far as the "air door" style "MAFs" go, I've only heard them referred to as "air flow meters" not MAF, they are a truly garbage design in my opinion.
Hopefully my new MS3 arrives tomorrow and I can continue with the setup and initial debugging of the rest of the electrical systems over the weekend, if it doesn't, I'll start working on fuel system plumbing and try and get everything else ready to roll as soon as it gets here. Maybe I'll pull the engine back out so I can paint the cradle and install the flywheel/clutch and have it ready to roll.
