BOOST pressure vs. MANIFOLD ABSOLUTE pressure vs. ATMOSPHERIC pressure - BOOST SCHOOL #4

Let's start with the basics. Air pressure or more specifically atmospheric air pressure. As we know, earth's atmosphere is filled with air. We are born and we die in this atmosphere, it's our natural environment, and this is why we don't really notice or feel the weight or the mass of air. But air most definitely has a weight and a mass.
All that air, the entire atmosphere, weighs about 5 million billion tons! So how come we don't get crushed by it? We don’t get crushed because all that weight is distributed evenly over the entire surface of the Earth. The average pressure you feel on your body is about 14.7 psi or 1 bar. But because you can't escape this pressure, and unless you've been to outer space, you never actually spent even a moment of your time without this pressure, you don't really feel it as you can't reference how it would feel without this pressure.

So what do you think, what's the place where you can feel the least amount of atmospheric pressure without leaving the earth? That's the top of Mount Everest of course, the highest point on earth. The highest point has the lowest pressure because it has the least amount of atmosphere above it, the least amount of air weight above it. The highest atmospheric pressure you can experience on earth if at sea level and the lowest is at the peak of mount Everest. But you can also experience very low atmospheric pressure if you contract a virus like Covid 19 and they put you into an isolation room. Many isolation rooms are actually negative pressure rooms. Inside a negative pressure room, the air pressure is artificially maintained at a pressure lower than outside the room, a pressure lower than atmospheric pressure. This is usually done with exhaust system that suck out the air of the room.
Because the pressure inside the negative air pressure room is lower than outside it, the contaminated air doesn't come out of the room when you open the door. Instead, clean air from the outside comes into it because air, like all fluids, always flows from a higher pressure area towards a lower pressure area.
Do you know what else works on the same principle as an isolation room inside a hospital? The cylinder inside your engine!
When the piston moves down inside your cylinder it creates a vacuum, or an absence of pressure. The cylinder moves down the bore at extremely high speeds and as it moves down it rapidly creates this void, or empty space, that for an extremely brief moment, has no air it, and as such is at a lower pressure than atmospheric pressure. But a turbo or a supercharger is capable of generating significant additional air pressure, and the air pressure inside the intake manifold of a forced induction engine can be double or triple that of atmospheric air pressure.

When you're looking at a boost gauge mounted inside a vehicle you're looking ONLY at the boost pressure generated by the turbo or supercharger. This means that a boost gauge isn't showing the actual pressure inside the intake manifold. It's showing the pressure inside the intake manifold - minus the atmospheric pressure. When you expose a boost gauge to atmospheric pressure it's going to show a value of zero. This is because a boost gauge and it's sensor are referenced to atmospheric pressure. The reason behind this is that you're only interested in what additional pressure your turbo or supercharger is generating, the pressure it ADDS on top of the atmospheric pressure, because that's what boost is, you're boosting your engine's power by adding more pressure than could be generated by natural aspiration i.e. the pressure of the atmosphere.

But things are different from the perspective of your engine's ECU. The ECU is interested in ALL of the pressure, both from the atmosphere and the pressure added by forced induction. It's needs to know all the pressure because it's trying to match all of the air mass with the correct amount of fuel. So the MAP sensor that reads pressure inside the intake manifold and feeds data to the ECU is referenced to absolute zero pressure. If you were to expose this sensor to the atmosphere it would read around 14.7 psi at sea level.

So boost pressure equals manifold absolute pressure - atmospheric pressure.
and manifold absolute pressure is: boost pressure + atmospheric pressure.

00:00 Atmospheric pressure
05:00 NA, Forced induction and Elevation
07:56 Boost pressure vs MAP
10:34 Stainless steel vs brass
12:22 MAP vs MAF in tuned boosted engines

A special thank you to my patrons:
Daniel
Peter Della Flora
Daniel Morgan
William
Richard
Pepe
Brian Durning

#d4a #boostschool #underpressure

[caig]

Still blows my mind that this amount and quality of information is being offered for free. Big respect!

[danielamorim]

I can't explain how well this series is put together. I am learning so much for my Gen 2 3SGTE swap into my ST162 Celica. Keep up the videos!

[MI-swiv]

Think I'm in love with this dude? Hope you know how articulate and concise your content is, it's veryy impressive! No teacher Ive ever seen can teach like you do with these videos !

[ibrahimqureshi]

your are literally the best instructor ever i appreciate you to spend your hard work and time just to explain something to us I have by far learned so much from your videos thanks!

[WanderingExistence]

2:48 Death Valley has 14.9 psi of pressure due to being a 280 ft below sea level

[firstielasty]

Light planes have an interesting variety of turbocharger wastegate controls systems. Some are as crude as a fixed wastegate that relies on the pilot watching the MAP gauge and controlling with throttle (yes, you can overboost them simply by firewalling it on takeoff), others are more sophisticated and actually regulate the manifold absolute pressure. They will maintain the set pressure throughout a climb until the wastegate is fully closed, at the "critical altitude" of the system, above which power drops with the altitude increase. Wastegates are usually hydraulically actuated by engine oil. The control systems modulate the oil pressure to the wastegate.
I added a MAP gauge to my turbodiesel RV...the gauge is from a multi engine aircraft (actually a dc-3). One port I left open, so it indicates ambient pressure, the other indicates MAP. I have driven it over the Rockies several times, interesting to watch both ambient and max MAP drop. Thus, available power drops proportionately..car people think their turbo negates the effects of altitude. Wrong, unless your turbo control system is designed to do so! It is probably not.

[shautohaus]

I honestly don't know how someone can explain something so complex, so clearly that I have zero questions at the end. Amazing.

[johnlovett]

Love the channel and this boost series. There's an occasional statement that's off from an engineering or physics perspective ... but that's not what this channel is about. It's about understanding what's going on rather then always speaking precisely. Put on your motor head hat and this channel is 100% binge-worthy, learning experience. Go D4A!

[TheMapleDaily]

I feel every day I watch at least one of your videos and learn so much in such a short amount of time, you really are efficient at teaching and staying on Much Love!

[jasonanderson]

New boost school!! Yes love this series👌🏼👍🏼

[csanton]

im learning a lot and this is free, you should receive value adding citizen of the earth award

[LandDrifter]

That's a great video! Thank you for sharing all this knowledge about engine tuning and physics principles. Just for record: 1 bar is around 14.5 psi, not that far from 14.7 but wanted to make it clear. Cheers!

[breathlessboarding]

One of the best teachers out there, keep up the good work!!

[FinlayDaGk]

WW2 fighter planes used turbochargers and superchargers so they could fly at higher and higher altitudes (which allows them to store more potential kinetic energy so they can start with a nice speed advantage when swooping down)

[Folderq]

Genious simply material, it will help the generations. Thanks !

[kapitainekram]

Another way to pass a MAF limitations is to devide your intake in 2, putting the MAF on only one side. It will then remain precise as it will measure only half of the air entering. Then you'll have to adjust the ECU program to take this into account (basically multiply by 2 the values related to MAF). If you want to be more precise by measuring exactly what's coming in the 2 sides, you can also use 2 MAFs, one for each side. Each will be measuring half of the air. You'll have to use a device between the MAFs and the ECU to add the 2 MAFs values and then send the result to the ECU.

[MI-swiv]

You're the best, no other channel or content on technical mechanics and cars compares !

[SUNUVAGUN]

There are places below sea level on land. The dead sea depression is negative 413 meters sea level.

[aaa]

Damn, those AEM plugs are smooth AF :D

Amazing videos, man. Quality is up the roof.

[ricobelcourt]

Thank you so much, all the other videos made no sense and only gave me little pieces of advice and left me confused. Full understanding now thanks to you