[greghoro]

Unless you have a Turbo, there is no pressure at the 5mm ports, it's vacuum.



Not sure what you are looking for, other than a specification. Perhaps you can elaborate on what you are trying to do.



If you are trying to tune or balance your carbs, the measurement is not important; what is important is that the two sides are equal. There are several threads in this forum on how to build a cheap device which is used to balance the two sides.



If there is a measurement, it would have to be expressed at a certain RPM, since the intake vacuum varies with the throttle opening. The more open the throttle plates, the less vacuum at the intake.



Growing up, I got to see this in person, as my mother had a car with vacuum operated windshield wipers. As she accelerated, the wiper motors slowed down. Accelerating up a hill, they would almost come to a stop. At idle, they ran fastest.

 

[greghoro]

For easier and quicker comparison of either side and you only have one measuring device, I suggest you make up a T.



Piece of hose to each port joined by a T in the middle going to the gauge.



Use a vice grip or some other means to alternately pinch each hose leading to the ports.



Disconnecting and reconnecting will most certainly affect the engine speed and therefore your readings. The mere act of measuring something impacts what you are measuring; you want to minimize this as much as possible (Heisenberg uncertainty principle).



Greg