Innovate Motorsports DL-32 - Manual (Page 19)

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8. Measuring Pressures
The DL-32 has a built in MAP sensor. To use it, connect a small ¼” hose between a
vacuum/boost connection AFTER the throttle body and the DL-32 MAP input port.
It should be connected after the throttle body because the lowest pressure that can be measured
before the throttle body is atmospheric pressure (discounting some pressure losses from the
intake tract before the throttle body).
MAP stands for Manifold Absolute Pressure. This means that the sensor measures pressure
referenced to absolute vacuum, not atmospheric pressure like many vacuum and boost gauges.
Engine parameters like fueling, ignition timing, compressor efficiency and so on are dependent
on the MASS of air (in pounds per cubic foot or kg per cubic meter) entering the engine. As air is
a gas, it’s mass is dependent on it’s ABSOLUTE pressure, referenced to absolute vacuum and
it’s temperature.
Most vacuum and boost gauges are gauge pressure sensors. A gauge pressure sensor
measures the difference to atmospheric pressure, not the absolute pressure. So, without knowing
atmospheric pressure at the point where the sensor gets it from, the actual air-mass entering the
engine can’t be measured. Because the atmospheric pressure changes with altitude and
weather, the gauge pressures are not a precise metric. This is specially problematic for boost
pressure sensors, because their atmospheric reference source comes typically from inside the
cabin or engine compartment. The atmospheric pressure there can change with speed from
aerodynamic effects (ram pressure).
8.1 Measuring MAP
Function 1 of input 4 of the DL-32 measures absolute pressure with a range of 0..1 bar (0..14.7
PSIa). This is the range intended for normally aspirated engines where the maximum intake
pressure can be atmospheric pressure.
Function 2 of input 4 of the DL-32 measures absolute pressure with a range of 0..3 bar (0..44.1
PSIa). This is the range intended for boosted engines where the maximum intake pressure can
be up to 29.4 PSI above atmospheric pressure.
8.2 Measuring boost/vacuum
The DL-32 can use it’s MAP sensor also as gauge pressure sensor if so desired. As stated
above, this is NOT the preferred way of measuring pressures, but it is possible. The DL-32 will
measure the current atmospheric pressure in the intake tract when it starts up and stores this
value internally until it is started the next time. In vacuum/boost measurement mode the DL-32
will then subtract the measured value from the MAP value internally.
For this to work, the DL-32 MUST be powered by a switched 12V source that switches on before
the engine is started, like the ignition power. This 12V source MUST stay active during cranking.
To give the DL-32 a chance to measure atmospheric pressure, you must change the way you
start the engine. First, switch ignition on (powering the DL-32), wait for 0.5 seconds, THEN crank
the engine (starter).
Function 3 of input 4 of the DL-32 measures vacuum with a range of 0..30 inHg (gauge) This is
the range intended for normally aspirated engines where the maximum intake pressure can be
atmospheric pressure.
Function 4 of input 4 of the DL-32 measures vacuum and boost pressure with a range -14.7 to
29.4 PSIg This is the range intended for boosted engines where the maximum intake pressure