Racah15 , You need to do some research. Your explanation of Speed-Density and MAS/MAF are wrong. /ubbthreads/images/graemlins/frown.gif (EDIT: Or they aren't wrong, and I'm just not reading you right! /ubbthreads/images/graemlins/wink.gif)
All the sensor methods discussed here correctly determine the mass flow rate into the engine. They are insensitive to changes in temperature through the intake-piping-turbo etc. The only advantage of knowing air temperatures going into the intake manifold vs. the intake pipe is how you adjust timing or boost. The computer will put the correct amount of fuel in, either way.
The only direct method I know of that measures the *actual* density, and thus mass flow, is a hot wire maf.
Speed density (MAP + AIT), Karman Vortex, etc rely on other variables or inputs.
The Karman Vortex only measures velocity. It needs to measure pressure and temperature at the sensor to calculate density, which can then be used with the velocity to determine mass flow rate.
The Speed-Density system knows the the density of the air via the MAP & AIT sensor, but not the volumetric flowrate. That's where the 'Speed' in speed density comes from. It's fairly easy to characterize the velocity of the air entering into an engine of a known configuration. You know the displacement, VE, compression ratio, etc. As your car is running, you also know the RPM. With the knowledge of the engine's characteristics combined with the RPM information, you can know with good accuracy what the volumetric flowrate of the air coming into the engine is. Combining that with the density, you get the mass flow rate.
The thing everyone needs to remember, is that any of these systems (SD, Hot-Wire MAF, Karman Vortex MAS, etc) are used ultimately to determine the mass flow rate into the engine. Velocity, volume, density, temperature on their own are meaningless if you can't use that information to determine MASS FLOW.
Why is MASS FLOW the term we care about? Because an engine is simply a machine that captures the mechanical motion due to the energy release of a CHEMICAL REACTION. And for chemical reactions, you MUST know what the MASS is of your reactants.
So now that the engine knows the MASS of air flowing into the engine, and how fast it's flowing in, it can then decided how much MASS of fuel to put in, and how fast.
I'll see if I can post up some equations.
So at the end of the day, all these systems do the same thing. It's just which one has the advantages we want. E.G. you can still drive with blown couplers, no MAS overrun, etc.
EDIT: Said 'Velocity' when discussing the SD system when I should have said 'Volumetric Flowrate'
