Carb-intake manifold-intake port matching

Rohan said:

Ah, suddenly someone is talking absolute pressures.

The vacuum gauge on the dash on most cars will commonly report 750+ mm of vacuum, in normal driving.
Descending hills, or decelerating from speed will pull this much vacuum.
Thats getting not that far from a complete vacuum.

Not that anyone here has ever mentioned achieving a complete and utter vacuum anyway...

Click to expand...

Pretty much everything that is OBD-1 compliant or newer that uses a MAP sensor instead of an airflow meter will give a reading in absolute pressure. There are even 2 (at least) Commandos on this forum that do as well. Where I live my Range Rover reads 98KPa wide open or not running, not zero. No type of piston pump is going to get close to zero, ever.

With OBD-1 we are talking digital versus / meeting analog here.
Name one bit of a stock Commando that is digital, in any respect.
The brake light maybe, it is off or on....

The nearest most here could get is a digital ignition unit...

The vacuum gauge on my dash could get near 800 mm of hg.
That is not that far from a total vacuum. ?

The point more is that the manifold operates near ALL of the time in conditions of a partial vacuum, to varying degrees, in otto cycle engines
Gently driven engines could be like that their entire life, if they didn't see any full throttle operation... ?
I don't see why that is controversial, in the slightest, its been like that for all of the near 140 years that otto engines have been around. !

Rohan said:

With OBD-1 we are talking digital versus / meeting analog here.
Name one bit of a stock Commando that is digital, in any respect.
The brake light maybe, it is off or on....

The nearest most here could get is a digital ignition unit...

The vacuum gauge on my dash could get near 800 mm of hg.
That is not that far from a total vacuum. ?

The point more is that the manifold operates near ALL of the time in conditions of a partial vacuum, to varying degrees, in otto cycle engines
Gently driven engines could be like that their entire life, if they didn't see any full throttle operation... ?
I don't see why that is controversial, in the slightest, its been like that for all of the near 140 years that otto engines have been around. !

Click to expand...

Why does it have to be analogue, you stated you had never seen a manifold pressure gauge in absolute?
How about some sort of reference to a vacuum being able to exert a force?

Cheesy said:

How about some sort of reference to a vacuum being able to exert a force?

Click to expand...

Vacuum powered, or boosted, brakes.
Vacuum powered windscreen wipers.

My father had a big industrial vacuum pump.
Commonly used in industry to power all sorts of equipment.
Like a compressor, but it sucks instead of blows.
Less dangerous if there is a leak, by far, than using compressed air.
Don't trains commonly have vacuum operated brakes.

Computer assembly machines commonly use vacuum lines to pick up the screws, to put them into motherboards.
10, 15 or 20 at a time, makes it quick and easy. And precise and consistent.

Heck, if you put your hand over the carby mouth to choke it, there is some serious vacuum there.
Get your clothes near there, it will try and drag you in.

Need we go on ?

Don't know where (or why) we are going with this,
some of this has been known for centuries...
The earliest industrial steam engines operated by pouring water over a big copper dome with hot air/steam in it,
so it cooled to a vacuum and pumped water.
Bearing in mind that vacuum and atmospheric pressure are 2 versions of about the same thing, one being the lack of the other...