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Optimising Tune With MAP/SD

Practical Reflash Tuning

Relevant Module: The 6 Step Process > Step 5: Optimising the Tune

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Discussion and questions related to the course Practical Reflash Tuning

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The Optimising Tune lesson only focused on MAF, but what about hybrid systems like LS engines where the MAF is not used under load? Should optimising the tune with SD be covered also?

One common method of tuning both systems used on GM engines, also applicable to the Mitsu Evo X actually, is temporarily failing one of the two systems at a time, so you can tune each independently. After tuning each system one at a time, you confirm they both calculate similar load/air mass under similar conditions, then enable both systems, and execute final small tweaks. If they aren't calculating similar load/air mass under similar conditions, then there's likely an error which you'll want to resolve before re-enabling both systems.

To temporarily tune SD only, you can set the max value for MAF failure to 0 Hz in the diagnostics section. To temporarily tune MAF only, you can set the max RPM for the dynamic airflow system to 0 RPM.

In terms of tuning each system, the operating principles section MAF then SD tuning are described, then MAF and SD tuning are discussed again in the Advanced Tuning portion of the course, and in the worked examples section there are a few GM HP Tuners examples which include MAF and SD tuning.

Info across the internet on this topic is a bit dodgy, and the MAF is actually used under load. Generally speaking the MAF is used in more stable conditions, but that can inlude the middle of a full throttle pull, while the SD system is used mostly in transients where there's a big swing in load/air mass from a large change in throttle position for example at the start of a pull. The portion of airflow calculated from each system isn't always easy to predict or monitor, so tuning the systems independently, then re-joining them, helps simplify the process, remove variables/confusion, and improves the result. I hope this helps clear things up!

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