What is speed density????
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From: Key West, Florida!
Car: 89RSconvtZZ4TPI
Engine: ZZ4TPI
Transmission: 700R4 TRIPP TRANNY
Basically (I'm not the sharpest crayon in the box 
) MAF or Mass Air Flow measures the amount of air flowing thru the sensor and into the engine to set computer settings. MAP (SD) Manifold Air Pressure measures intake manifold vacuum to tell the computer what to do. MAP is probably easier to work on but I've heard MAF responds better to modifications.
edit: 1000 POSTS!!!!!!!!!! WOW LUCKY YOU!
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Rob P
89RSconvtZZ4TPI
Edelbrock Hi-Flow Intake
SLP Dual Cold Air Intake
1 5/8" Headers
Semi-Siamesed Runners
MSD6AL/AdjFPR/IROC frnt@rear swaybar/wonderbar/steeringbox/alum drvshaft/ Alston SFC/3:23posi disc rear/MAC LCA/H.Adams Panhard Rod/KYB struts/ shocks/
92Z28convt5spd
71Impala convt 402BB
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[This message has been edited by Rob P (edited June 07, 2001).]
) MAF or Mass Air Flow measures the amount of air flowing thru the sensor and into the engine to set computer settings. MAP (SD) Manifold Air Pressure measures intake manifold vacuum to tell the computer what to do. MAP is probably easier to work on but I've heard MAF responds better to modifications.edit: 1000 POSTS!!!!!!!!!! WOW LUCKY YOU!
------------------
Rob P
89RSconvtZZ4TPI
Edelbrock Hi-Flow Intake
SLP Dual Cold Air Intake
1 5/8" Headers
Semi-Siamesed Runners
MSD6AL/AdjFPR/IROC frnt@rear swaybar/wonderbar/steeringbox/alum drvshaft/ Alston SFC/3:23posi disc rear/MAC LCA/H.Adams Panhard Rod/KYB struts/ shocks/
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!
[This message has been edited by Rob P (edited June 07, 2001).]
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Doogie,
Rob is a sharper crayon than he is letting on. He covered the basics pretty well.
The speed-density control scheme uses a MAP sensor to measure the pressure in the intake, and the TPS to monitor throttle position. Between these inputs and the engine RPM reference signal, the ECM calculates the amount of air entering the engine to determine the correct amount of fuel to meter through the injectors. This is the same somtrol scheme used on TBI engines. The advantages to the SD scheme are simplicity, ease of diagnosis, and low cost. They are also more suited to adapting to higher-flowing engines because they lack the restriction of a maximum flow rate as is found with the earlier MAF systems. The disadvantages of the system are poorer fuel metering due to presumptions about the air density and flow at a given throttle angle and manifold pressure or vacuum. Because of this, any modification that changes the intake vacuum rates affects the fuel calculation, and usually negatively. A new cam profile almost always requires teh addition of a custom PROM designed for the engine setup, and any other changes affect the fuel rates accordingly.
The MAF system uses an air mass meter to actually measure the mass (weight) of the air entering the engine. This enables the ECM to control fuel very precisely, regardless of vacuum. The advantages are exact fuel metering, more adaptability to engine modifications, and more exact diagnostics provided by the ECM. Installing even an aggressive cam grind in a MAF system may not require the change of PROM, since the MAF measures the exact amount of air entering the engine. The disadvantages of the MAF system are higher cost, and a limit of the ECM firmware (not PROM) of 255 grams per second as a maximum measureable air intake. For most engines, this is adequate, but for some engines may mean that the mixture can become lean at higher RPM and intake flow.
It's interesting to note that the earlier ThirdGen TPI engines used the MAF system, the later ThirdGens used the SD system. The TTAs and other GM cars that got the turbocharged 231 V-6 used a MAF throughout their existence, regardless of what was happening in the V-8 world.
Oddly (and appropriately), the fourth generation cars returned to the MAF system to make more power and produce fewer emissions. The newer MAF systems lack the measurement restriction found in the older ECMs, however, so the LT1 and later engines have the best of both worlds. Ironically, they also use a MAP signal as a reference check for the MAF.
Still confused? I am....
------------------
Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader
Rob is a sharper crayon than he is letting on. He covered the basics pretty well.
The speed-density control scheme uses a MAP sensor to measure the pressure in the intake, and the TPS to monitor throttle position. Between these inputs and the engine RPM reference signal, the ECM calculates the amount of air entering the engine to determine the correct amount of fuel to meter through the injectors. This is the same somtrol scheme used on TBI engines. The advantages to the SD scheme are simplicity, ease of diagnosis, and low cost. They are also more suited to adapting to higher-flowing engines because they lack the restriction of a maximum flow rate as is found with the earlier MAF systems. The disadvantages of the system are poorer fuel metering due to presumptions about the air density and flow at a given throttle angle and manifold pressure or vacuum. Because of this, any modification that changes the intake vacuum rates affects the fuel calculation, and usually negatively. A new cam profile almost always requires teh addition of a custom PROM designed for the engine setup, and any other changes affect the fuel rates accordingly.
The MAF system uses an air mass meter to actually measure the mass (weight) of the air entering the engine. This enables the ECM to control fuel very precisely, regardless of vacuum. The advantages are exact fuel metering, more adaptability to engine modifications, and more exact diagnostics provided by the ECM. Installing even an aggressive cam grind in a MAF system may not require the change of PROM, since the MAF measures the exact amount of air entering the engine. The disadvantages of the MAF system are higher cost, and a limit of the ECM firmware (not PROM) of 255 grams per second as a maximum measureable air intake. For most engines, this is adequate, but for some engines may mean that the mixture can become lean at higher RPM and intake flow.
It's interesting to note that the earlier ThirdGen TPI engines used the MAF system, the later ThirdGens used the SD system. The TTAs and other GM cars that got the turbocharged 231 V-6 used a MAF throughout their existence, regardless of what was happening in the V-8 world.
Oddly (and appropriately), the fourth generation cars returned to the MAF system to make more power and produce fewer emissions. The newer MAF systems lack the measurement restriction found in the older ECMs, however, so the LT1 and later engines have the best of both worlds. Ironically, they also use a MAP signal as a reference check for the MAF.
Still confused? I am....
------------------
Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader
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