umop apisdn
Join Date: Jun 2014
Location: Brisbane, Australia
Posts: 469

Intake Air temp (IAT) and Manifold Air Temp (MAT) are both important things to measure for any engine.
What we need to consider is if and where they are needed in the fuel calculation.
In a speed density EFI System, the only way the engine can measure the amount of incoming air is to calculate using pressure & temperature against RPM and Volumetric Efficiency. So generally MAT is the important measurement along with manifold pressure, so the MAT sensor should be very close to the point in which the MAP sensor is connected. The end result is still a calculated guess, but that's all we have available in simple speed density systems. If we want to get really picky, external barometric pressure/temp, intake manifold pressure/temp and exhaust back pressure measurements are all needed to accurately represent the true mass of air in the cylinders.
With CIS, because the air plate is actually a Mass Airflow Sensor, the above speed density calculation is not required. The air plate is measuring the weight/volume of incoming air and altering the fuel delivery ratio to suit. Therefore FrankenCIS is now not responsible for the base fuel calculation and delivery and actually performs a trim function with the additional sensor information available.
Assume the air plate and fuel head is delivering a theoretically correct AF ratio, then manifold Pressure is now a representation of actual air in the manifold and therefore a multiple of CIS calculated air/fuel in the engine. Manifold air temp is now a variable in calculation of true boost pressure rather than necessary for determining fuel delivery.
For trim purposes on a Normally Aspirated engine, sensor placement near the Air Plate is sufficient, for a boosted engine the sensor should be placed in the airflow as close to the MAP sensor point as possible but insulated from engine heat. Optionally the IAT/MAT sensor can be disabled in the settings and used purely for data logging or even never installed if you wish.
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Steve
1981 928S 4.7 ROW with KE3Jetronic and Franken8 (AEM Inifinty) follow at [http://www.frankencis.com/ActivityFeed/userid/2]
Yes! mechanical/hydraulic constant flow injection can be managed by a modern EMS
www.FrankenCIS.com
