| Karl is correct, the MAP is a calculation and the MAF is a actual measurement. The Maf measures the exact amount of air going into the engine, this tells the engine ECU to give the proper amount of fuel to go with the amount of air it reads.
Both have benefits, but for a street car the MAF is more consistent from car to car and it can more easily compensate for modifications your doing to the car.
The Maf is easier to tune and will have less drive-ability issues, as long you do not install a blow off valve.
A Map sensor reads vacuum and boost, this calculates the amount of air as the vacuum goes away and the boost raises. A maf sensor can compensate easier for changes in the system because it reads the air the engine receives.
A map sensor will require more tuning for small changes.
Lets say your running stock cams and your vacuum is 18 inches at idle.......Now you put in JWT cams that run 4 degree advance on the exhaust......Now the engine only pulls 14 inches of vacuum.....This will cause a map sensor to add fuel and cause a rich condition at idle. The MAF will know if more or less air is really going into the engine, so it will not cause a rich condition at idle when you change cams. The plus to a map system is it is much easier to plumb, and you do not need to worry about direct air flow on the air filters and and it is easier to remove restrictions in the intake system.
Blow off valves have no effect on a map system, because it only reads what the motor is doing and is not looking at what is happening in the pipe system. The last thing to touch on is the other way to use a MAF sensor....
The Z32 Maf system sucks air, with this system when air is blown into the filter from wind it gives the MAF wrong information. This system also has issues with blow off valves, because the turbo still sucks air when the blow off valve releases.
The other way to run a MAF is a blow through system, this places the MAF between the turbo and throttle body. With a blow through system you can have a blow off valve after the turbo and before the MAF and the blow off valve will not effect the MAF readings. Also air flow on the filter will not effect the readings in the blow through system.
The biggest reason this is not common on a Z32 is because of space, and the fact that the stock system works very well and there really is not a need to change it in most cases.
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