Quote: Originally Posted by TJ1376
And hey, the MAP SENSOR doesn't measure the volume of air going into the engine, the NGC calculates that based off the amount of pressure the sensor reports AND a table based off the amount of air the turbo can flow at given pressure.
Thats why ported and clipped stock turbo's are so neat... You can leave them setup on stock controlled boost lines, and the NGC has no idea you are FLOWING more air, because your pressure never increases.
Super close. Technically it could care less what turbo you have bolted to it. It's going to provide a certain response/output for certain inputs, and that response/output (timing and fuel) may be tailored for the stock turbo, but it doesn't directly look up somewhere in its programming a stored value of what the stock turbo flows. Instead it calculates it.
The NGC should just be using the the pressure, IAT, rpm's, and engine displacement along with factors like the pre-programmed volumetric efficiency. The intake air charge is a gas and things like density (mass/volume) are affected by pressure, volume, and temperature (since the gas itself molecularly isn't changing). So the PCM knows the temperature (IAT) and it knows pressure (MAP), so it can calculate volume. And if it knows volume and the mass of normal air (which is a constant), it can compute density. So it has ways to figure out just about anything it needs to. How it goes about this is currently unknown to the general public until it gets hacked and we can see the equations and tables it uses together. (And it
shouldn't use table-
only look-up and cell comparison like older cars, but some tables still
should be there to use in equations and algorithms to calculate fueling and timing requirements under specific conditions.)
If you port and clip a stock turbo the compressor side isn't really changing and it's moving the same amount (mass) of air per shaft revolution. What has changed is the exhaust side. You've removed restriction which should increase volumetric efficiency. So you could think of the turbo trying to push air in but now the exhaust side is flowing better so exhaust gasses can get out to the tail pipe easier. If the exhaust gasses flow better the burned intake charge can flow out easier to take place of the exiting exhaust. Now if this slows down the turbine then the compressor would also correspondingly slow down (i.e. perceived lag/delayed boost) but also may not choke it up top and allow the compressor to pump more air though at higher rpm's
For the most part at higher boost levels on a stock turbo compared to the same boost on a bigger aftermarket turbo, the big turbo willl be more efficient at compressing the intake charge (efficient = cooler = denser = more oxygen molecules to burn) and the exhaust side will be more efficient so overall efficiency and power will increase.
There was another long thread where I was discussing this with someone else already. I'll just say that the NGC should be programmed to work with the stock turbo and work well within it's operational characteristics, but it doesn't have a "flow look-up table" and instead uses algorithms and known lookup characteristics from the other sensors to determine the amount of air (if my educated guess is correct). Also consider that if the computer sees characteristics like
xx boost and
yy IAT's and it may produce a output (fuel and spark) tailored to the stock turbo. So even with a big turbo at a certain boost pressure combined with other variables it may still dump a lot of fuel or do something with timing because it would be better for operation with the stock turbo.
I've got to be really careful when talking about this subject because it really should be broken down a lot further in-depth, and while trying to give a broad overview it's possible to skew the interpretation or not get a point or idea across correctly. I try though.
Here's another link I was able to find again with some good graphical and text description of gas characteristics:
http://wright.nasa.gov/airplane/eqstat.html
