Any "Scientists" on here? or maybe Engineer

OK, I have noticed on some cabs the Vacuum port for the distributor is Very small - like .030" hole and on others it is as large as .125". In a carburetor vacuum type signal, where it is reliant on the source being the flow through the carb, will the size of the hole change how much vacuum signal the vac advance on the dist. sees? In other words will a larger hole pull more vacuum against the diaphragm?

 

I don't think it changes total vacuum, just the rate of change, acts like a moderator on rate of change

 

I'm thinking...not a scientist, but I've worried over the same thing...that actual depression/vac delivered will be the same, BUT small hole is going to take longer to move the diaphragm/piston/part being controlled because it has to evacuate the excess air in there for it to reach lower pressure and do what it is supposed to do. Delay may be a feature in a dashpot or carb mixture control...bring in what it does slowly rather than bang.
Things that work by flow tend to be fairly big, but of carefully chosen size, like the orifice in a PCV system, so the vac moving air is moving enough air without leaning out the engine.

 

It depends what the vacuum port is trying to do - if it's trying to suck the crap out of something and create a flow, then it will be big enough to suck that amount through - like a crankcase vent system.
If it's just to provide a signal or level of vacuum and not trying to flow air through it, such as with a vacuum advance, then size doesn't matter (no matter what she says), the pressure will be accurate all the way along the tube.
Cheers.

 

I posed a similar question the MegaSquirt guys as they were the brainiacs in the Tuner realm, and I needed their help in a setup.
I asked about response time with small diameter .06" ID hose and length affecting response. Their answer was: that the signal or rate was not reduced (slowed) due to length.
Admittedly a carb would seem to depend upon diameter and passage length.

 

I think the answers above are correct - the size of the hole determines how quickly the vacuum in the hose can be changed, i.e. how quickly and to what extent the distributor learns about new vacuum levels. Evidently the designers did not want the distributor to see instantaneous vacuum changes, either up or down.

Regarding the idea that hose length and diameter do not matter: Suppose the hose had an ID of 12 inches, or the hose was 50 feet long - it's easy to see that the distributor would never hear anything from the vacuum source.

 

For a given size diaphragm, the small hole should just delay the action.

Another way to look at it...you could still put 35psi in your tire through a 1/8" hose, it would just take longer.

 

While the diameter of the port will impact the rate of change of volume & pressure, I think the size of the diaphragm + vacuum line will also impact the signal. A larger volume will cause a smaller change in pressure than a smaller volume (Boyle's Law). So depending on how sensitive you want the signal from the carb, different volumes and diameters could be used.