Stephen Max

iTrader: (59)

I have a question concerning hot wire maf sensor operation.

DAVE Sz

iTrader: (2)

Are you thinking that maybe the heat from the engine changes it's resistance and the readings it sends to the ECU?

Stephen Max

iTrader: (59)

No, I'm wondering if a pound of pressurized air has the same heat transfer characteristics as a pound of air at atmospheric pressure.

I'm thinking the answer is yes (meaning that it doesn't matter if you put the maf before or after the blower), within the temperature and pressure ranges boosted cars run at, but it would be interesting to hear from someone who is knowledgeable on the subject.

Jeff92se

iTrader: (82)

LOL!

xsnowpig

iTrader: (1)

its been 15 years since my thermodynamics, heat transfer, and other such classes, but i'll give it a shot.
assume air is liquid that's just less dense. if you pressurize liquid, you distinctly change the thermodynamic properties of that liquid - think pressure cookers- change in boiling points, etc.
when you pressurize gas, you are stuffing more mass in a isovolumetric space (whoa, that's a $0.50 word!). many things happen there.
it heats up.(when you fill a rigid steel container with compressed air it gets REALLY hot!)
it also gives more mass to transfer heat around (think about dropping an icecube in a cup of boiling coffee vs. dropping it in a pot of boiling water - which melts faster?)
how does this apply to the MAF location? i don't know. The key question is what property is the MAF is actually measuring. volume/time? mass/time? mass/volume/time? mass/volume (pressure)?
if somebody else can come up with what the MAF actually measures, we can go from there.
school's out!

Quicksilver

iTrader: (1)

Yeah..a fun question! Let me think about what exactly you're asking, first...

By heat transfer characteristics, do you mean if the air (pressurized vs regular 14.7 PSi atmosphere) can depart more heat to another conductive material by flowing past/around it? Or just by "sitting" around said material? Maybe I just don't understand what you're asking at all...

hotshtsr20

doesnt matter if you put the MAF before or after as long as the system is sealed.

since pressure and temperature (and heat transfer) curves are linear (or close enough), it would affect the hot wire proportionally to its actual air MASS, regardless of its pressure.

so, to answer your question: no.

the only $hitty thing about putting the MAF after the compressor (whether turbo or supercharger) is you expose it to much harsher conditions than it would experience at low pressure. on turbos especially, as they tend to blow a constant stream of oil (albeit small amounts) into the air stream.