Inlet Manifold Pressure Using Estimate Table

[Herrubermensch]

I am running a supercharged BMW S62 with an M190 and *may* choose to do so using alpha n as a proxy for load rather than a MAP sensor, based on erratic MAP readings at cruise levels from the individual throttle bodies. Two questions about doing so.

First, when I fill out the manifold pressure estimate table in the engine setup workbook, it uses a percentage for manifold pressure, not kPa. What is this percentage of? Percentage of maximum kPa as set in the efficiency table? Why is this not an absolute value so that I can populate a typical rpm vs. throttle percentage vs. kPa table? The properties don't seem capable of being changed to an absolute kPa value.

Second, assuming I select "estimate" as the basis for computing inlet manifold pressure, is that going to use the same value for computing differential fuel pressure? Blown S62s historical use alpha n for the fueling table, but will rely on a post-throttle body vacuum reference for the fuel pressure regulator. M1 Tune does not appear to permit this: either inlet manifold pressure is determined by sensor or by estimate table and cannot be determined by sensor for computing differential fuel pressure and by estimate table for fueling. Only solution appears to be using a differential fuel pressure sensor.

Advice and direction appreciated.

--Peter

[Stephen Dean]

Having a percentage value for that table is correct, as it is an estimate of how full the manifold is, in comparison to the reference pressure that you have used when setting up the Inlet Manifold Pressure Estimate Mode. If you have used Ambient, then it is the percentage of the Ambient Pressure that is being used. As an example, if we have a Ambient Pressure of 101.325kPa, and the Inlet Manifold Pressure Estimate Table has a value for the load cell that you are in of 44%, then the calculated value will be 101.325 * 0.44 = 44.583kPa, however, if your Ambient drops to 95kPa as you have driven up a mountain, then the calculated value will be 95 * 0.44 = 41.8kPa.

If you use 100kPa Relative for the Mode, then the calculated value will always be calculated against 100kPa, so a value of 44 in the table will always be 44kPa, with no adjustment for changes in Ambient conditions. If you are using a ITB engine, with no Manifold Pressure Sensor, then this is the recommended mode to use, if you have an AIrbox or Ambient Pressure sensor, then use Ambient Pressure Relative to get a better result.

With the Fuel Pressure, if you have the M1 setup to use 100kPa Relative as the mode (recommended for ITB's) and a MAP sensors as well, then the M1 will use the MAP sensor value to calculate the Differential Pressure on the injectors.

[Herrubermensch]

Thanks, Stephen. That makes sense.

My package--a highly modified version of the GPR--lacks "100 kPa Relative" mode. I have as options under "Inlet Manifold Pressure Mode" only "Automatic," "Sensor" and "Estimate." Under "Engine Efficiency Mode," I have manifold and ambient as pressure reference options. I do not have an option labeled "Inlet Manifold Pressure Estimate Mode." My M190 has a development license, however, so I am sure I can add these options. Any guidance on how best to do so? I will ping my developer/Motec dealer as well. Thanks again.

--Peter

PS: One follow up question. Obviously, with an engine running forced induction, the max kPa will be in excess of 100 kPa, in my case between 240 kPa and 250 kPa. Thus, the percentage in the Inlet Manifold Pressure Estimate table will need to exceed 100%, but the range appears to be limited to 100%.

[Ben-S]

You should consider using inlet manifold pressure mode and setting up the map sensor to "fail" under a certain voltage. That will cause the system to switch to the inlet manifold estimate table during low load conditions but still use speed density for high load and RPM.

You could do this a lot cleaner in Build without having to set a false failure point in the sensor setup but the end result will be the same.

[Herrubermensch]

You should consider using inlet manifold pressure mode and setting up the map sensor to "fail" under a certain voltage. That will cause the system to switch to the inlet manifold estimate table during low load conditions but still use speed density for high load and RPM.

You could do this a lot cleaner in Build without having to set a false failure point in the sensor setup but the end result will be the same.

That is an excellent idea! I will try my hand at some code in Build this weekend. Call it "hybrid" mode, with a simple "if then" logic that kicks inlet manifold pressure mode from "estimate" to "sensor" after kPA, as measured by the MAP sensor, hits a set point, probably just a few ticks above atmospheric pressure. So whenever in any material amount of boost, MAP sensor governs; below that, the estimate table governs. But you are right: setting the sensor to "fail" at the voltage below the set point would accomplish the same goal. A really great idea that accomplishes the same thing as a 4D table, but much simpler. Thanks, Ben.

--Peter

[Herrubermensch]

Thanks, Stephen. That makes sense.

My package--a highly modified version of the GPR--lacks "100 kPa Relative" mode. I have as options under "Inlet Manifold Pressure Mode" only "Automatic," "Sensor" and "Estimate." Under "Engine Efficiency Mode," I have manifold and ambient as pressure reference options. I do not have an option labeled "Inlet Manifold Pressure Estimate Mode." My M190 has a development license, however, so I am sure I can add these options. Any guidance on how best to do so? I will ping my developer/Motec dealer as well. Thanks again.

--Peter

PS: One follow up question. Obviously, with an engine running forced induction, the max kPa will be in excess of 100 kPa, in my case between 240 kPa and 250 kPa. Thus, the percentage in the Inlet Manifold Pressure Estimate table will need to exceed 100%, but the range appears to be limited to 100%.

Just to respond to my own inquiry here for the benefit of others on the forum, "Inlet Manifold Pressure Estimate Mode" is part of the updated GPR package. If you don't have it, you need to update to the latest GPR package, which has greater functionality and is much easier to use. As for the range, I just adjusted it in properties.

--Peter