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MAF vs Speed Density System - what's the difference?

10K views 36 replies 12 participants last post by  falchulk 
#1 ·
On the Allpar website, it states that the hemi uses a "speed density system"
to measure airflow. My '04 mustang used a MAF (mass air flow). So, if the
hemi uses speed, wouldn't some sort of ram air be better than cold air?
Just asking, as I am just a hairy legged previous owner of a red SE.
 
#5 ·
The article says that the speed density has no ability to measure airflow.
So by replacing the stock airbox with a cone filter does nothing but make noise. Even if more air was flowing in, the computer could not detect it.
So all these $300 cone filter systems make a nice vrooooom noise, but nothing else.
 
#11 ·
I am not knocking the open air cone filter setups. When I installed one on my
mustang it gave it a real macho sound, which I liked. After which I dropped
the mufflers and went with cats only. That drowned out the intake noise entirely. When I mash the pedal on this SRT-8 it is quite loud with an all
stock set up. I am being very tempted to get one of the open cone designs
just to make me feel even more testosterone enhanced. That's what this is
all about, right.:grin:
 
#14 ·
so your saying that by adding exhaust and cai to the stock charger you get no gains. do we get the gains by chipping the car.I also have been told that we must get the chip reprogrammed for every mod after the chip was added. This means mod out our cars and then chip it after fully modding. Are all chargers controlled by fly by wire.
 
#15 ·
Basically, this is how it works:

Speed density systems, like the Charger has, work by measuring the inputs of various sensors, comparing the results to a pre-configured set of tables in the computer, and then sending the corresponding outputs to the fuel injectors to maintain close to the 14:1 mixture. The tables are programmed near the top and bottom ends of what the engine is known to accomodate.

Mass air flow systems measure the amount of air coming into the engine differently (directly), and then the computer calculates how much fuel to add to create the appropriate mixture on the fly. Although limited, major changes can be accomodated.

This means that major changes (more than the stock set of tables can accomodate for) aren't going to be accompanied by a corresponding increase in fuel, and you will actually harm the engine by running lean (too much air, not enough fuel).

Chip programs (after a mod or alone) change the tables that the PCM uses to determine how much fuel to send into the engine. Added a large amount of air via some new mod? Flash the PCM so the fuel values in the tables are increased to match the additional percentage of air coming in...
 
#16 ·
One thing that is missing in this discussion is "Adaptive Strategy"

This is a method for adaptively controlling engine calibration control values. The strategy includes the steps of:

(1) predicting a driving pattern based on analysis of recent past driving patterns

(2) selecting engine control values appropriate for the predicted driving pattern and a desired emission constraint.

The adaptive strategy adjusts spark timing and magnitude of EGR as a function of engine energy usage per distance traveled while maintaining feedgas emissions at a constant level over a wide variety of driving patterns including urban, suburban and highway.

A plurality of driving cycle segments are analyzed to generate a table of engine calibration control values for the adaptive spark and EGR control strategy.

This adaptive strategy has fuel consumption characteristics which are most advantageous at the most constrained feedgas levels.

Drivability can be enhanced because of the greater calibration flexibility inherent to the adaptive technique.


<vendor comments removed>

Brian
 
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