MoTeC Global Forum

Two related questions, arising from considering changing the tune on my BMW S54/M190 from MAP-based to alpha-n:

First, when selecting throttle position as engine load normalized mode and estimate as the inlet manifold pressure mode in the GPR package (as you recommend for engines running ITBs), why doesn't the fuel table utilize engine load normalized on the Y-axis rather than an estimate of inlet manifold pressure? Put differently, it would seem to make more sense when using these settings for ITBs to have a percentage value of engine load normalized (i.e., throttle position) rather than estimated inlet manifold pressure on the Y-axis. This, of course, is how the ignition table is setup, viz., with a percentage value for engine load normalized (i.e., throttle position) on the Y-axis and RPM on the X-axis.

Second, what impact if any is there on the fuel table from changing engine load normalized mode itself? There would seem to be none, and that the principal determinants of how the fuel table works are engine efficiency mode and inlet manifold pressure mode.

Please disabuse where appropriate. Thanks.

--Peter

Nevermind! As further evidence of encroaching insanity, I'll answer my own question!

When setting inlet manifold pressure mode to "estimate" then deactivating the RPM axis in the inlet manifold pressure main estimate table, one can establish a one-to-one relationship between percentage of inlet manifold position to throttle position, making the percentages in the fuel table throttle position percentages. I suppose if one really wanted to make this clear, one could change the name of the axis in M1 Build, but taking these steps effectively allows one to use throttle position percentage as the Y-axis in the fuel table a/k/a the efficiency table.

--Peter

Since creating this thread, I became aware of the ITB tuning methodology for M1 Tune in the following document:

https://www.motec.com.au/filedownload.p ... docid=5973

Essentially, this technique takes the approach of zeroing out the engine efficiency table and tuning fuel via the manifold pressure estimate table rather than zeroing out (or inserting plug numbers in) the manifold pressure estimate table and tuning the engine efficiency table with throttle angle on the Y-axis in lieu of manifold pressure (which is the method called for in the M1 Tune setup menu). It further calls for (i) Engine Normalized Mode to be set to "Normal" rather than "Throttle Angle", (ii) set Manifold Pressure Estimate Mode to "Airbox Pressure Relative", (iii) set injector location to before throttles regardless of where actually located, and (iv) set Fuel Timing with End of Injection earlier than 380 degrees BTDC for light to medium loads and with no guidance for higher loads.

I would appreciate someone explaining the advantage of this method over the method called for in the M1 Tune setup menu.

--Peter

I really want to know more about this also. Can’t see any logic. But I guess motec knows what’s best…

I can’t see why I can’t use tps with a boost compensation. Or can you?

To the top! Anyone at Motec care to weigh in? I can tell you from working with multiple club racers running ITB BMW engines and M1 ECUs that there is a LOT of confusion about this.

--Peter

Herrubermensch wrote:To the top! Anyone at Motec care to weigh in? I can tell you from working with multiple club racers running ITB BMW engines and M1 ECUs that there is a LOT of confusion about this.

--Peter

+1

There is alot of confusion. Im confused lol. A base map with this configured with guideline/general values would be awesome.

Or release an ITB turbo designed package for us with this setup.

I will cover off the main points asked in a bit of a dot point form:

- The prime advantage of using the method described in the tech document CTN0036 is that the fuel film has a more accurate representation of the manifold pressure to work with.

When you set the manifold estimate table as a 1:1 for the throttle position, the fuel film needs to be recalibrated to suit this artificial relationship. When the efficiency main table is set to 100, and the estimate table is populated, the fuel film references these estimated manifold pressure values for fuel film calculations. As the fuel film is tied to a manifold pressure value that responds instantly (as it is tied to throttle position), some combinations will require less fast part in the fuel film compared to if it was calculated off a real manifold pressure sensor reading.

- The fuel injector location influences how the fuel injector differential pressure is calculated. It will take in the fuel pressure estimate and regulator type, or in the case of a fuel pressure sensor being present the fuel pressure value for the pressure behind the injector. With before throttle Airbox referenced selected, it uses airbox pressure in place of inlet manifold pressure estimate (for a naturally aspirated setup with ambient pressure as a fallback) or use the boost pressure sensor for above ambient pressure for the pressure at the outlet of the injector.

- When Inlet manifold pressure mode is set to estimate, you gain two efficiency compensations - Engine efficiency airbox pressure compensation and Engine efficiency boost pressure compensation. It should be noted that the airbox pressure compensation should be used for the change in engine pumping efficiency from the airbox pressure - this is not used for changes in ambient pressure. Ambient pressure changes are calculated for automatically with the ambient pressure reading, or ambient pressure estimate on power up.


When the system is setup in accordance with CTN0036, the fuel table is relative to throttle position.


Your Engine load normalised challenge will greatly influence the behaviour of things such as your ignition timing. If it is relative to throttle position, it fixes the behaviour of the ignition timing to the throttle. Using normal for engine load normalised, it is closer to a representation of the behaviour of engine load normalised when a manifold pressure sensor is fitted. Setting to throttle also has no provision for you to adjust the ignition timing into boost, as the engine load normalised tops out at 100% with the throttle, and there is no clean way to accommodate the need for less timing under boost. When it is set to normal, this will allow the engine load normalised to track above 100% into boost.

I'm currently working on a base setup for a turbo charged ITB equipped engine, I have to sanitise it first (it's off a file supplied by an external tuner) and then validate it, but I am planning on having it available shortly.

SDean wrote:I'm currently working on a base setup for a turbo charged ITB equipped engine, I have to sanitise it first (it's off a file supplied by an external tuner) and then validate it, but I am planning on having it available shortly.

Did you get anywhere with this Stephen?

I had been working on it, and then my laptop failed it's hard drive so I'm still rebuilding my files from that. I'll get back into this shortly.