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[Maladjusted]

The TTS tuning guide states:

"Manifold Pressure is measured by a sensor in the intake manifold.  This sensor responds to "absolute" pressure - in other words it can read vacuum as well as pressure somewhat above atmospheric.  Absolute pressure is measure in relative to a perfect vacuum, ant the units of measurement are Kilo Pascals (kPa).  Zero kPa is a perfect vacuum, while 100 kPa is atmospheric pressure at sea level, approximately 14.7 Psia.

The Harley MAP reading a idle is typically 30 to 40 kPa, while under full load the MAP will read close to 100 kPa."

Here is where my confusion lies... if 100 is atmospheric pressure at sea level, wouldn't that mean there is zero pressure and zero vacuum??  and... at full load, wouldn't the intake manifold experience the most vacuum? putting the kPa reading at a lower number.. like 20 or 30 kPa?!?

I am thoroughly confused.

Mal

[Steve Cole]

The throttle blade is what creates the difference in pressure between the intake manifold and the atmosphere. The engine is trying to pull in air and the throttle blade stops it, so the pressure drop occurs in the manifold. When the throttle blade is fully open there is nothing to stop the air from entering the engine so under this condition the manifold should equal the atmosphere. Since the atmosphere at sea level is ~100 kPa that would be the expected reading.

[Maladjusted]

Ahh... that helps!  Thank you sir.

Mal