Subaru Maf scale

I ran into the MAF issue with a 03 USDM WRX. I also have an 02 that has a lot less mods. I've pulled the tunes for both cars and compared the MAF scales. The 03 has a lower maf scaling than my 02, which I believe has stock scaling. The 03 is currently way outrunning the MAF and I'm just looking for some input as to why someone would have scaled the maf down?

Running into the airflow limit happens with mild modifications on the ECU so it's common practice on the 02-05 WRX to scale the MAF down to avoid the 300g/sec limit if you aren't using a custom operating system to overcome this. Sometimes called half MAFing the tune, if you half all MAF cal values and double the injector scalar (or half the injector flow rate depending on the software you're using), you get a net zero change in fueling, but double the actual airflow before you hit the hard airflow limit. Keep in mind this massively impacts calculated load, so all tables and values relating to load must also be rescaled to suit for this to work properly, and some software does not have all the impacted tables exposed, so be careful.

If you only need a little headroom you can do the same thing, but with smaller changes such as taking 20% out of the MAF cal and load axes values, making the inverse change to the injector scaling.

This makes sense. I haven't completed the entire reflash course yet, but I'm working it now. When we got the car it was not running and somewhat apart. The tune I pulled had 750cc injectors, and I didn't know about halfing the MAF scale yet, so I put DW 750cc's in it, but I do not know what injectors were previously in there. It would make sense to me that it was rescaled for that reason. Do you recommend that I go back to stock injectors for now, or keep the 750s? I am not having any AFR issues, but was having a boost creep problem prior to installing a 4 bar MAP. I don't feel like I need much more from the MAF, I don't hit the high circuit issue until 19-20psi.

If you’re flowing enough air to max the airflow system out, you generally would be needing injectors that flow more than stock.l so 750 sounds reasonable.

In terms of figuring maf scaling out, you are working with less variables when injectors and injector data are stock.

if you have time, I would run stock injectors at low boost, with stock injector data, get the maf scaled as far as you can on stock injectors, then switch to the larger injectors. The reason for this is the 750s don’t come with data that allows for proper injector characterization, so that complicates and throws off MAF scaling. This way at least you know what MAF scaling should be, before throwing the variable of the injectors in.

You can certainly skip this step and still get the car running, but if the goal is learning, it’s the order I would do things in.

Thank you for the help. My goal is definitely to learn and keep the tune safe right now. Since I don't know what was in there before, I think I'll try this and get a good starting point before going back to the larger injectors.

Awesome. You're very welcome. Happy tuning.