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Why modern cars use MAF sensor instead of speed density?

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almost every car I've worked on, owned, are MAF based.

from JDM to European and Ferraris..... the only OE I can remember that uses speed density is Honda.

but the standalone ECU tuning industry mostly favor speed density. why is that?

MAF is more tolerant of changes which would require retune on speed density or damage states.

For example, collapse a factory catalyst on a speed density, it will run pig rich if not miss in the top end, MAF, it will still run albeit with muxh less power.

Fit various bolt ons, within reason and MAF tune will self compensate, it picks up the changed mass flow at the "same" speed density tune point.

Likewise the difference between a "good" and "bad" factory engine (manifold castings/gasket alignment, port volumes etc) could likely require significantly different speed density tune (not allowing for long term trims or knock control) where MAF will be very close to target AFR and required ignition as you are in the general vicinity on the mass/rpm map curve even if they are a bit different.

A blown intake pipe on a suck through MAF is the foil however. Then again most modern ecus still have MAP/TPS backup.

However, setting up a MAF sensor can require more care, and before some of the relatively modern wide range options there were limitations on factory sensors. Speed density as a cheap and cheerful aftermarket alternative is far more flexible if you are selling a fairly generic wire in or patch loom or even multi-compatible pug in ecu in terms of cost and flexibility of installation arrangements. Stepping up to IMP:EMP recovers some of the tolerance/adaptability of MAF tune models without the MAF limitations.

well explained.

i guess another benefit of MAF is the ability to account for elevation change? since it calculates actual "mass" instead of volume

I visit mountain area in the 2700-3000meter elevation frequently and would like to drive my GTR, is there any practical way of compensating elevation change for speed density tune?

Yes, intake and exhaust manifold pressure sensors or intake manifold and barometric pressure sensor.

Using intake to exhaust pressure ratio vs rpm as main VE table with afr target based on boost vs rpm is fairly common.