I agree, let's not. However, when the piston moves downward, the cylinder is filled via atmospheric pressure. Not from partial vacuum. The intake valve is open, there is no absence of air. Hence the term "normally aspirated", as opposed to, I dunno, "partial vacuum aspirated"?

It's all right here, gents.....https://en.wikipedia.org/wiki/Bernoulli's_principle Thought I'd also include this for the "vacuum" questions....https://en.wikipedia.org/wiki/Vacuum These are the "facts". Not trying to be sarcastic or a smart-a$$ in ANY way. This is for clarity and accuracy. It's very easy to use words in ways that don't apply to their true meaning. Everyone does this from time to time. But, I think, generally, this "board" prefers the evidence to "back up" statements and examples. And, that's a good thing! As used to be the tag line for the "National Inquirer"....."Inquiring Minds Want to Know" LOL Cheers!

What you said is ONLY true if there is a restriction to airflow.

Ummm......restricting airflow does not create a vacuum. Restricting airflow creates changes in the pressure and velocity of a fluid (of which air is one).

So......


Have you run the engine without an intake manifold yet? :D

"where did my sandwich go?......i swear i had it right here....."

https://en.wikipedia.org/wiki/Manifold_vacuum
this might shed even more light since there seems to be a difference between how 'a vacuum' is defined and how 'manifold vacuum' is operationalized
From the article esp re: diesel engines-
Manifold vacuum in diesel engines[edit]
Many diesel engines do not have butterfly valve throttles. The manifold is connected directly to the air intake and the only suction created is that caused by the descending piston with no venturi to increase it, and the engine power is controlled by varying the amount of fuel that is injected into the cylinder by a fuel injection system. This assists in making diesels much more efficient than petrol engines.

If vacuum is required (vehicles that can be fitted with both petrol and diesel engines often have systems requiring it), a butterfly valve connected to the throttle can be fitted to the manifold. This reduces efficiency and is still not as effective as it is not connected to a venturi. Since low-pressure is only created on the overrun (such as when descending hills with a closed throttle), not over a wide range of situations as in a petrol engine, a vacuum tank is fitted.

Most diesel engines now have a separate vacuum pump ("exhauster") fitted to provide vacuum at all times, at all engine speeds.

Many new BMW petrol engines do not use a throttle in normal running, but instead use "Valvetronic" variable-lift intake valves to control the amount of air entering the engine. Like a diesel engine, manifold vacuum is practically non-existent in these engines and a different source must be utilised to power the brake servo.

Basic Physics
 

" What you said is ONLY true if there is a restriction to airflow. " .

I see .

So then, you have a <magic> engine that doesn't draw in any air at all ? .

Pretty cool .

Even if there's almost zero vacuum the simple fact of less than atmospheric pressure necessary to draw air into the cylinders means : vacuum .

This is a fun thread .

I have not. I haven't done anything with the car, yet. Life gets in the way, sometimes. Without going into the boring details, my E300 had to a back seat for a while. Glad I have the 240D which I use for my work commute.

Never, in my wildest dreams, would I have guessed the legs this thread has grown. I'll have admit, I'm still a bit nervous about the whole thing. Doesn't seen like I have much choice, though. I'm gonna remove the over head pipe first, run it like that, and see what I can see.

Hopefully sooner, rather than later....

Pictures or it never happened...... :D

Hahaha.....ok, I promise to post pictures.

Which is, by definition, a vacuum, as its lower pressure than atmosphere.

What is a vacuum, anyway?
 

Nice try. But, nope. NOT, "by definition, a vacuum". Lower pressure than atmospheric does not constitute a vacuum.
Atmospheric pressure changes are dependent on altitude. If you stood on top of a 5,000 ft. mountain, there would be less atmospheric pressure than at sea level. You would not be standing in a vacuum. This is very basic science. Like, grade school level science.
Restricting airflow does not change atmospheric pressure. Once again, it changes pressure and velocity (which, by the way, are inversely proportional). As a fluid (air) approaches a restriction, pressure increases and velocity decreases. As the fluid (air) exits said restriction, pressure decreases and velocity increases. A very basic example of this is when one places their thumb over the end of a garden hose (for the purpose of increasing velocity). This is not my opinion. It's simple science, proven well over 100 years ago. This increase in velocity is what you're mistakingly calling a vacuum.

I'm sorry you skipped out on middle school science class. But, yes, it literally does.

vacuum | ˈvakˌyo͞o(ə)m | noun (plural vacuums or vacua | -yo͞oə | )
1 a space entirely devoid of matter.
• a space or container from which the air has been completely or partly removed.

https://en.wikipedia.org/wiki/Vacuum#Relative_versus_absolute_measurement
"Vacuum is measured in units of pressure, typically as a subtraction relative to ambient atmospheric pressure on Earth. But the amount of relative measurable vacuum varies with local conditions."

Correct, it changes manifold pressure, which becomes lower than atmosphere pressure.


A partial vacuum.




Which you have proven you do not comprehend. Thank you.

Uh, Oh ~
 

Yet again we agree , you phrased it far better than I did : • a space or container from which the air has been completely or partly removed.