Originally Posted by ProECU
The MAP pressure sensor has the same operation throughout the rev range in that its a sensor which measures pressure and "Vacuum" to some extent SO in terms of High revving NA, it is as important as low revving NA.
The job of the map sensor is to tell teh ECU how much fuel/ignition is required at a particular MAP vs RPM setting. How do i know this, well ive decompiled the bin file (ala hondata) and read the code.
The MAP sensor does NOT compare the outside pressure AT ALL. It has certain boundaries, a min/max value as a check for sensor validity. If the voltage exceeds these tolerances, a code (CEL) is returned.
tinkerbell is incorrect by stating that vacuum determines power, this is NOT the case. The ECU will only see vacuum from the MAP sensor under idling, or when you back off the gas pedal.
Power is determined by the quality of the burn in the combustion chamber (a/f) and the ignition (adv/ret) combined with many other factors such as engine load, fuel quality etc.
Cylinder filling on the other hand, is a product of piston velocity and also a process commonly known as scavenging. This is the process by which cam overlap causes a low pressure condition in the cylinder head, hence mixture is drawn from high pressure to low pressure, increasing the amount of fuel at any given combustion process.
Manifold pressure is not directly related to the combustion process. Take for example a forced induced application.
You have probably heard people talking about B16's as being a torquless motor, this is due to the low piston speeds (long rods) at low rpm.
On the other hand, the D-series motors have more torque and are "nicer" to drive at low rpm's (smaller rod -> faster piston speeds)
This is somewhat of a side-track, but hopefully an insightful one.
ProEcu
