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Under hood Air Flow Effects on MAF Calibration

EFI Tuning Fundamentals

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I run a 2011 STi that had a motor rebuild and pro tune by Antspec in LA. I recently added hood side louvers to help keep coolant temps on the track under control. Would this change in airflow and pressure in the engine bay warrant a recalibration of the MAF sensor?

The video would seem to suggest not, but does not directly address this scenario.

Not normally.

Not sure about Subaru MAF ( I would think they are no different to MMC) but Mitsubishi MAF got inbuilt temperature and baro sensors so they would automatically adjusts MAF readings to ECU...

Good question. It really depends on the intake system used. When I worked on the COBB Redline intake, for example, I tested it with the hood down, hood up, we blasted air into the hood scoop, then the front end inlet duct with a leaf blower, we blasted air around the engine bay with the leaf blower and more. This was all after flow bench and standard dyno testing, and it led to a system that's really robust in maintaining proper airflow measurement as airflow around the intake system changed.

Other intakes which aren't as well shrouded and sealed from what's happening in the engine bay do not fare as well. To some extent you can tweak MAF scaling for this, but if the reading is impacted by underhood airflow, generally it's not predictable or consistent, so it is not something you can tune out in the calibration.

Thanks for the reply’s! Great info. I went down some rabbit wholes and had Yimisport check the car out. Came to the conclusion that best guess is I got a little water in the intake on that track session, because it was wet. Though unlikely with the SF intake box, I believe the rain had a good chance to get in there through the vents prior to getting out on track. This likely caused the misfire and spark plug fouling. Then i started monitoring the knock for the first time so closely and started obsessing over it. Which it has too much knock to not address it, but also not a catastrophe. When Yimisport took a look at it, they also verified that the tune on the car, though a professional job, isn’t suited for how I use it. The target AFR under full load is never lower than 11.1. Which for extended track use he said was too lean.

im taking it back to them for a retune and installation of a air temp sensor in the intercooler to have better management under heat soak conditions (running TMIC). He felt confident that if I just stuck to 101 Octane I could keep running it as is, but I’m just waiting till the retune.

anyway, that’s way more info than anyone wanted to know. Thanks again for the reply’s and info! I’m going to keep at getting educated and maybe I can get to fixing my own tune issues one day.

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