MAP / MAF whats the difference?

[944turrboo]

Im looking to buy a new MAF sensor but now i hear something about changing to a MAP whats the difference between the 2 and whats better reguarding more power for the buck

[Scott R]

M Mass
A Air
F Flow

M Manifold
A Absolute
P Pressure

Two different was of sensing air flow and pressure. I too would like to know how each differs as it pertains to the 951, I would imagine that both will work excellent. I would bet that it comes down to who has the better software in the end.

Are yopu considering the "Guru" Map kit? I keep trying to find someone that has one that I can drive to compare with.

[ae1969]

The arguments for the use of either is looooooooooooongg.....

In the end you can argue either way on what is better. In theory MAP would have greater potentials but you also run into some tuning issues.....

If you decide to go MAP, danno at Guru's is the only way to go. www.gururacing.net (read the tech info)....

I was dead set on MAP...... but ...things change.

The choice I made was a combination of a number of factors....

The things that made me choose in the end were.....

1. Numbers.... the product has to produce!
2. All in one solution..... (a complete bolt on solution)
3. Pricing... (comptetive pricing.... not a giveaway cause everyone has to make money)
4. Service... (I expect emails to be returned at least within a day or two........not 2 weeks later!)

I was so close on getting Danno's Map 2 kit. He seems like a great guy/tuner and I would be hard pressed to find someone who understands how these cars work better than him.

That being said...... I ended up going with a stage 2 from Vitesse.

I will let you guys know how it goes............

[944turrboo]

Theres so many MAF kits out there.. and i found that the Autothority kit is made by Pro-Flow and its wayy cheaper on there website... but there are so many flase claims out there on HP gains. I was thinking of either a Huntley Racing Kit or a Lindsey Racing MAF. With the MAF kit do i need to upgrade my DME and KLR chips?

[turbohead7]

There are many arguments about these two popular sensors. The thing they have in common is that they both measure engine LOAD. The Manifold Absolute Pressure sensor emits a signal based off of engine vacuum, or pressure. In a NA engine vacuum decreases as RPM increases therefore the engine controller can calculate the fuel requirements across a broad range of circumstances. The true benefit to these sensors is that the incoming air that the engine breathes does not have to flow through it, therefore there is no further restrictions for the charge which can be extremely beneficial to engines which spend the majority of their time above 5,000 RPM. They are much cheaper than MAF sensors, which makes them a first choice for many manufacturers. A more accurate yet restrictive way of measuring engine LOAD is with a Mass Air Flow sensor, also known as a Hot Film sensor. These sensors use a heated element which is situated directly in the air-stream. The incoming air cools this element proportionally depending on how much air flows over it. When the airflow increases, the element temperature decreases and based on this cooling cycle and supply voltage monitoring a signal is generated to the DME. New versions of these sensors even incorporate an Intake Air Temperature sensor integral to the unit. Although accurate, these are the most tempermental sensors ie: dirt, water, etc... Lastly, 944's use a different type of mass airflow sensor---a Vane Airflow sensor. This particular sensor is quite accurate and reliable. Using a potentiometer mounted on a trap door, the sensor changes it's 5v reference depending on the vane's position. More air and the door opens and vice-versa.

[1.2gees]

I will attempt to clarify what's been discussed above:

Manifold Absulute Pressure sensor has it's advantages, such as theoretically near "zero" restriction for measurement purposes, which is ideal. However, the amount of air that the engine is using is calculated, from the measured amount of pressure present @the measurement point (usually very close to the intake valves). This can introduce several (albeit small) problems, such as the varying pressures in the manifold (valve pulses, etc.) or limited resolution. It also has it's advantages such as cost, and the fact that air leaks before the manifold will not effect fuel ratio much.

Mass Air Flow sensors operate very similar to the "Vane" type sensors 944s were equipped from the factory. Their workings are described accurately by turbohead7 except for the fact that the MAF sensors use a "hot wire", the wire is kept at the same temperature, the amount of current used to keep the wire at the same temp. changes depending on air flow, density, and temperature. The amount of current is what's monitored, not the temperature of the wire (as the temp. of the wire is constant). MAF's include a "cleaning" cycle, most after, some before operation where the wire is super heated to burn off any deposits, to remove film or other accumulation. Usually MAFs are very reliable also.

I believe the ultimate solution would be to use both MAF and MAP on the same car, and many manufacturers do this, though it's not very cost effective.
Ahmet

[turbohead7]

Thanks gees. The element or "hot wire" as you call it does cool; as a matter of fact it is constantly heating and cooling---depending on airflow----as I stated. You see gees, as the element heats up, it's resistance increases and the amperage through that element decreases. When more airflow travels through the sensor it carries away heat or COOLS it. reducing the temperature/resistance and increasing the amperage. Therefore, based on this COOLING CYCLE the DME reads this change in current as a change in airflow. So you see gees, if amperage is going to change, then the resistance must also change. And how does the resistance change, gees? By the temperature change of course. Geez gees.

[1.2gees]

Well, we could go into detail...

Basically the hotwire (which is a wire, or more commonly multiple wires BTW I'm not calling it this, it is a wire made of platinum, and this is it's name, "hot wire") is kept at roughly the same temperature (ambiant +~180) as the engine is operated. The principle of hotwire sensors revolve around keeping the "wire" at the same temp. If I recall correctly, earlier mass air flow meters used a thermistor, accompanying the "hot" wire. Obviously the job of the thermistor would be to generate a signal that corresponds to the temperature of the wire. Depending on this signal, the voltage applied to the wire would vary, keeping it @ the same (or if you'd like, "the ambient +~ 180 degrees F) temperature. This all took place within the unit, and only the voltage required to keep the wire at the same temp was relayed back to the engine control unit. Generally a value between 0 and 5 volts, higher corresponding to increased air flow. Since the process of maintaining wire temp took around 3 miliseconds, I did not say that the temp of the wire fluctuates. Good catch there, it actually does.

Your definitions can vary, and that's fine w/me. Anyway, later MAF use more than one wire, and calculate the ressistance across only one, by using the wheatstone bridge principle. A new voltage is applied to the wire, to keep the wire @ operating temp, and thus operating ressistance, which again is 180 degrees F above ambient. Newer MAFs respond, adjust, and produce a signal in about 1.5 miliseconds. 1.5 miliseconds is indeed longer than 0 miliseconds, so you're right, the temps do fluctuate. I'm guessing this definition suits you better?
Ahmet

[turbohead7]

Well--------I thought my first explanation more than suited the questioner's needs, apparently it didn't suit you.
Luke

[1.2gees]

Don't mind me, I get that way sometimes...
Ahmet

[944turrboo]

i think imma go with the MAF.. why not it seems to be working for everyone

[todwic]

MAP sensor systems are more apt to be less accurate the more the engine wears, than AFS/AFM/MAF sensor based systems are. Where I to have to choose which one to use, I would look at a veteran injection system manufacturers. I'd look at Bosch's chronology, since they have thier fingers in everyone's pie, and have pat pends on most of the diff. styles of pies on the market. Thier pulsed injection systems go like this: D jectronic MAP based system. 1960's to late 70's early 80's. They then went to the L-jectronic (L = Luft, german for "air") to replace archaic D. Of course the motronic M.1 is brains behind this operation. It uses the vane type AFM. Engine has to be in "perfect working condition" before service on these systems can take place. Then they evolved to the LH-Jectronic (LH=luft (air) + Hiesse (sp? german for hot. ) These guys have the Motronic M.2 brains came into the scene. Of the two choices, I'd go with the hot wire system, its the newest technology and it's not so dependant upon engine wear.