MAF vs MAP , my notes

[Bruce]

Both accomplice the same thing.

MAF:
Uses a heated wire, or foil that is maintained at a constant temp., the
amount of current used is an indicator of how much air is flowing past it.

MAP:
Uses a diapham, mounted as a strain guage in a Whetstone bridge, to generate
a signal referenced to a vacuum. So any variance in pressure generates a
variable voltage, as referenced to an absolute.

Both, with only compensate to limited degee for any programming errors.
There is no better of the two for those errors, they both have a fixed range
of BLMs.



The MAF system *tends* to be a little more forgiving in some mild
applications because the sensor is remotely mounted, and hence mechanically
dampened. Whereas the MAP is plumbed right to the plenum, so it sees any
modifications with less dampening. The lack of dampening also means, more
responsive, you'll never get the absolute throttle response of a MAP system
with a MAF.

There will ALLOWS be some lag time when using a MAF sensor, because of the
thermal lag in the actual sensing wire/foil. You can shrink the size of the
sensor, like in the newer ones like the LT1 / LS1 but you can't eliminate
it.

In a steady state condition the MAF will develope a better average signal
then MAP. Again, it's about dampening.

Since the MAF is pre TB, air filter ducting changes affect how it responds.
Also, if major can throw off the MAF tables. removing the screens, does
nothing but induce errors into the system. Sometimes they might help,
sometimes might hurt. Sometimes help in one place and hurt in another. Best
way to eliminate guessing what is going on is to leave them alone. If you
look into a LT1/LS1 MAF you'll note two (well actually 3) sensors. 2 are
mounted on opposite sides of an airflow, to help eliminate any sensing
errors, these two are averaged. Now these are the state of the art ones, and
GM has taken the time to make them this complex, might think about how much
money that cost, all in an effort to get the sensing right.

MAF Math:
Grams/sec=CFM*.5663
1.3 CFM per 1 HP
.75 Grams/sec = 1 SAE HP

The stock MAF is rated at 255 (early v8 TPIs) grams/sec. If your engine
consumes more air then that, your out of calibration resolution, not a good
thing.
What you and others can do, is set the fuel for WOT, and then just run rich
till you get to peak airflow. As a last resort, it's even a poor idea. I
will grant that there are 9 sec GNs doing that, but I still don't see why
folks do that when there are options available.

The ecm only knows what you tell it, and then uses that info to generate
answers. You have to figure out the MAF scalers, or figure out the VE table.
Personally the VE style of calibrations are a ton easier for me. The
accuracy of any tune is how the fuel and timing are done in these areas.
Both take time to get right.

Accleration enrichments.
Depends on calibration code, but the one huge difference is that the MAP
system has a MAP correction for Accleration, meaning the code handles AE,
and for the MAP systems corrects for actual LOAD. You just can't do that
with MAF since it has that lag from the sensor. They both have a coolant
temp, and TPS correction.

MAF sensors are always alot more expensive then MAP ones

Both can be fooled into errored readings from reversion. At lower throttle
openings the MAF is just a tad better for not being in error as the MAPs.

Remember 20% throttle opening is exposing 70% of the air flow thru the TB.
This explains why large Butterflies seem to be better (at part throttle), by
the buttometer, and can actually cost performance. It's just at the lower
openings they are flowing more air at the same opening so they seem
**peppier**

Using the LT1 VE tables are a good starting point for many MAP systems,
YMMV.

The only way to find out what the engine wants is testing, testing, testing
testing testing. Information about what is really going on and how it
applies take hours of work. Sometimes it's easier to build an ecm bench to
get a grasp of what's going on.

Which is better?.
It all depends.
For response and WOT performance the MAP will win, when done right. If for
no other reason then the restriction of the MAF sensor itself. MAP systems
don't care about engine flow, so aren't displacement sensitive.
Just to confuse things thou, some newer systems use both, which can give the
best of both worlds.
Final Answer
Final Answer
Bruce



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