Ok.. a little late to this game, but I spent some time discussing ecus, fuel trims, and the maf mod with cap Years ago.. you are WAY over thinking things… at one point cap(or someone else) ran the stock intake through a flow bench and found that the amount that the stock intake could flow is well above what is required for a stock 1zz, so your calculations of more airflow based on less obstructions, for all in tens I’ve purposes are null and void in this case. The math and theory of it is awesome though!
the part, and magic, that you’re missing is that of the MAF sensor itself. The MAF sensor reads the volumetric airflow based on a “hot wire”. The more airflow running overtop of that wire, the more it is cooled, and the sensor registers this and provides a voltage from 0-5v. The veins in the stock intake direct air over that Hotwire, and the ecu uses that reading And it’s internal calibration to create a short term fuel trim. That short term fuel trim along with an O2 reading is used to create an internal map, or correction to the fuel trims and creates a long term fuel trim.
now, the ecus internal map using rpm and maf voltage to pull fuel trims, ignition timing,vtc, etc out of each “load cell”.
well, what happens if you reduce the maf voltage being sent to the ecu? It will think it’s under less load and will read the data from a lower load cell.. what’s in a lower load cell you ask? Well increased timing because at lower load levels, knock is less of an issue amongst other things.. on the flip side, whats also in lower load areas? Less fuel.
less fuel and increased timing beans the ecu has to compensate for due or throw a cel.. if the fuel trim ends up being greater than X then it can’t fully compensate and it will throw a CEL.
so, we need to counteract the fuel issues, or the fuel trims will be way off. How do we do that? we add larger injectors or increase the fuel pressure, so now the ecu pulls fuel out and creates new fuel trims. The difference is now we’re within the allowed short term fuel trim to create a long term fuel trim..
So now we’re left with a lower voltage maf voltage because our maf is no longer receiving as much airflow on the Hotwire. Out ecu thinks we’re in a lower load cell causing increased timing, but less fuel, so we add more fuel by larger injectors.
hopefully this clears some stuff up….
Oh.. in terms of an aftermarket intake, what I would recommend doing is finding out the surface area of the maf sensor and then subtract that surface area from the area of a slice of the intake pipe…. Calculate the potential flow/voltage registered by the maf based on the area/surface area/flow over the hot wire based on it being in the are/pulled out of the air, etc.. a 2.5” intake vs a 2.6,2.7, etc. will all register different voltages and will cause a different load cel to be read and reflect different timing, fueling, vtc, etc.