Okay i have been around cars and racing them for awhile so i am not new to the whole "engine" thing, BUT i always see people talk about 3.5 Bar Map or bar map...i have a general idea what it does and where its located(on top of IM).

BUT can someone please explain in details how it really works, and whats the difference between the JDM ones and USDM ones or whats the difference between 3bar and 5 bar. Thanx

 

its just referring to how high it can read. The JDM or evox map sensor is a 3bar. The USDM evo 8-9 come with a 1 bar map sensor.
Map(manifold absolute pressure)
1 bar = 14.5037738 psi

 

that makes sense, BUT what does it actually do?? Is it how much the IM can flow per certain time??

 

Manifold absolute pressure. Map sensor reads the amount of pressure in the intake manifd I.e. Boost. 14.7 psi is = to 1 bar. When you start messing with your car and turning up the boost you need to be able to read more than that. Aem makes a 3, 3.5, and 5 bar. 5 bar generally works for anyone in the Evo community since we tend to run alot of boost. The lower the bar though the more exact it is.

For speed density you need ait and map. Air intake temp and pressure reading(map sensor). Both are used together to calculate the amount of fuel needed for air fuel ratio.

If that doesn't answer I will try and explain more later but I'm on iPhone and it's a pita.

 

It's simply a sensor to measure the pressure of the air in your intake manifold. The answer to your question depends on how much boost you intend to run.

 

so if you are running lets say 35 psi, then you need to change the bar map?? whats the max boost that you can run on the stock ones??

 

To log boost of up to 35 PSI you need at least a 4-bar sensor.

"One" bar indicated one unit of atmosphereic pressure and it works out to about 14.5 PSI.
Since you are measuring the ABSOLUTE pressure inside the manifold that is already under at least ONE bar of pressure all the time(at least on earth) it is actually mearsuring from a negative(vaccum) of 14.5 PSI.
In a sense, a 1-bar sensor (like the USDM evo8/9) basically is only used to activate the EGR system so it's pretty much useless once you start modifying/removing the EGR. It is not used to log boost (possitive number you see on your boost gauge).

To record the boost of upto 14.5 PSI (on the boost gauge) you will need at least a 2-bar sensor. Upto 29PSI you will need a 3-bar and up to 43.5 PSI you would need a 4-bar sensor.

 

sooo if iam running 21psi and the boost gauge says 21 psi (even right now with the stock 1 bar map), do i still need to change it to a 2 bar map??? btw i get the whole atmospheric pressure thing and what 1 bar eqauls to, im just trying to understand the whole bar map thing and if its worth changing it unless i am making crazy power

 

Not necessarily, the factory map sensor is only good to 1 bar as has been stated. 1st off we are talking about a 0-5v sensor. So the ecu sends 5 volts to the sensor, as pressure in the intake mani increases so does the resistance of the sensor. Its not always exactly this way but the important thing to understand is its a linear relationship. This is why operating range is important, since no matter the size it is a 0-5v sensor you loose clarity and response as you go larger. You want enough to be able to read the amount of boost you want to run, but not so much as you only use half the sensors range.

What most people overlook is vacuum. The map sensor reads that too, so with the car turned off and the key to run the map sensor should be reading 1 bar. So given that 1 bar is about 14.7 psi a 3 bar map sensor has a range of 44.1 psi, but now subtract the portion of the sensor range that is for below atmospheric pressure and you get 29.3 psi which theoretically is all this sensor is capable of registering.

So now you might be wondering how the heck the factory 1 bar is reading boost, answer is simple... it isnt. If you log it with evoscan you will see it gets too about 1-2 psi and flatlines. The reason this is no big deal is because the evo ecu is metering the air via the MAF sensor. The factory MAP sensor is mostly their to take a barometric pressure reading the moment you start the car, this helps with fuel trims as the ecu has a better idea of elevation and air density.



There are two types of fuel injection, mass air flow and speed density. Mass air meassures the amount of air entering the intake and speed density estimates the airflow based on a few key sensors. This is why I prefer the MAF, even though it is an intake retriction.

 

you would only need to change it if you want to convert to speed density and elimnate the maf or you would like to log boost instead of eyeballing the gauge.

 

perfect sense now thats more clear...thanx