hi guys i realize our cars use a MAF sensor (Karman vortex) for load reference but i see thats its mounted on the inllet of the turbo.. how does the ecu know its into Boost when the MAF is before the turbo???? doesnt there have to be MAP sensor somewhere?

thanks

 

it "sees" how much air passes through... and makes the appropriate calculations for fuel. it doens't matter what boost you're at... it matters how much air goes into the engine... on a hot day you could be at 20psi but you'll not be seeing half the air as on a cold day at 17 psi... (that was just an analogy not real calculations).

 

so every MAF car has to have a MAP sensor somewhere, correct?

 

Nope, it can just have a MAF sensor.

 

I believe there is a MAP sensor on our car but it's only rated at 1 bar. Someone correct me if Im wrong.

 

Here is a brief description of how a MAF sensor works....

MAF Sensors
Mass Air Flow (MAF) Sensor is used by the engine control unit (ECU) to determine

the weight of the air going into the engine. To do this, Subaru uses a cylinder

shaped sensor mounted securely to the stock air cleaner box behind the

passenger side headlight assembly. Inside the sensor there is a special wire or

film which is kept heated to a certain temperature. As air passes through the

sensor, this wire or film is cooled and the sensor determines how much electricity

is required to keep the wire up to temperature. This enables the sensor to d

determinehow much air (in weight) is passing through the sensor at any given

moment. This signal is then sent to the ECU which it compares to a

preprogrammed map to deliver fuel and ignition spark, taking into account other

engine inputs such as engine RPM and temperature

 

thats how a hot wire works but the maf in a evo is a honey comb

 

do you have a picture of what the inside of the sensor looks like?

 

Karman sensors count how many waves pass through it. We have a Barometric Pressure Sensor, but it has nothing to do with boost. Less pressure it sees, less air in the waves the Karman sensor is counting, the less fuel the ECU injects.

The honeycolms kinda look like this 2g's (but we only have one main chamber);
http://www.roadraceengineering.com/e...wbackedout.jpg

 

why it alters maf signal when u put open air filter? not on stock air box with lid open?
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let me rephrase that: Every Turbo MAF car must have a MAP to read boost! ???


thanks!

 

it alters it because the maf reads vortexes... or waves int eh form of vortices... so when you create turbulance, better known as non laminar flow, it messes up the readings.

 

the answer is still no, ours does not have one, and hence does not need one.

 

Boost that we talk about in turbo land is really just a pressure difference that exists between the outlet of the compressor and the intake of the motor versus ambiet air pressure.

Think of it like a baloon ... if you take a volume of air in the baloon, and the baloon is say like 3psi above ambiet, the baloon is a certain size.

You take and squeeze the baloon and the psi inside the baloon goes up to say 5psi. But the same amount of air molecules are in the baloon.

The same thing happens in our EVOs. X-volume of air goes through the MAF and gets registered as X-volume of air. When it gets compressed, the computer really doesn't care other than the MAF just saw X-volume of air and it will mix the appropriate fuel with it.

Of course the bigger the MAF signal, the more volume of air the EVO is sucking down, which really means that you're producing more boost.

Hope that helps,

jcnel.

 

We do have a mdp sensor tho