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136(?) | How Altitude Affects your Tune

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I missed the live webinar, but was one of the people interested in this topic when it cropped up recently. I was just wondering:

- do you (Andre, or anyone) have any reason to think that IMAP/EMAP isn't the best way to lookup VE when using speed density? I'm definitely onboard with it being so (engine is an air pump, etc), but can't shake a concern that there are some situations at a given rpm where pressure ratio is the same but load different and also VE might be different. Now MAP can account for the load difference, but could VE be different too?

- totally related to the above, how does the 86 go with the new axis? Does experience match theory yet?

- I assume there is no other use for IMAP/EMAP? - it's not appropriate for lambda target or ignition

- to make sure I have this the right way around in my head, a good fault value for the EMAP sensor (which can be prone to failure - its a tough life) would be 101kpa, yes? For a typical engine under boost, I think in a fault situation this would give a higher PR and hence likely to be failing richer?

I've got a Link and am some way away from it running, and hoping Link will introduce this before I need it (or even better - a couple of maths channels - I naively assume either is easy). If not I think I can loop a GP output back in as an input with frequency representing IMAP/EMAP, if I am keen to give it a go. Link lets you use a DI as the fuel table axis.

I can't personally say whether IMAP/EMAP is the ultimate way of defining engine load for the VE lookup table. Certainly it makes sense to me but so far I haven't been able to do sufficient testing. There are also some issues with the injector calibration on the 86 which are potentially affecting the shape of the VE table currently and hence the accuracy. Consider this a work in progress. What I can say so far is that the engine tunes just as well using PR as it does using TPS or MAP as the load axis. It also drives just as well using all three.

No IMAP/EMAP is not suitable for ignition or lambda target. The ultimate way of defining the load axis for ignition (IMHO) is to use the calculated mass airflow. This is the typical load axis in a OE ECU that uses a MAF. It will normally be represented as g/cyl or g/rev. The problem here is that this mass airflow is derived from the ideal gas law which takes VE into account so if you change the VE then it affects where in the ignition table you end up.

A fault value of 100 kpa for the EMAP is probably as good as you can hope for. At least it should get you home in an emergency. Ultimately any fault value is going to result in an inaccuracy somewhere but as you say, this 'should' be the safest option.

Thanks - I appreciate the detailed reply as I was disappointed to miss the webinar live.