[Trevor]

Tony, please consider.

The pressure gauge you have purchased appears to have only one point of connection and therefore measures pressure above atmospheric, which means that without modification it will not do the job you have in mind.

Unless the intake airbox is placed at an advantages position and the car is in motion, there can be no positive pressure of any consequence within the intake manifold. Your experiment requires the measurement of pressure developed across a restriction from inlet towards outlet, rather than against atmospheric.

This could be achieved by mounting your gauge within a rigid transparent container so that it can be viewed, with the existing inlet brought to the outside, and with a second connected to the interior of the container. This arrangement could provide two connections and a means of pressure measurement between the inlet and outlet, of any anticipated point of restriction within the manifold, at various engine speeds and load.

Alternatively you could use a sensitive vacuum gauge and measure the negative pressure at the point of entry and exit of the restriction and make a comparison. However this method would not be as efficient.