So I've got a few questions... Just been messing around trying to learn more etc.
So the MAP sensor on the manifold. It's obviously post throttle, which at idle should be in vacuum. Right? However it shows like 5 psi on the Accessport. Looking at Cobb's site, I see the Boost Pressure monitor is "MAP minus barometric pressure" which is 14.7 psi... okay, so to me this doesn't make sense. If I were to put a hole in the manifold and stick my finger over the hole, I would feel it sucking my finger in.
I've run into this weird (at least in my head) way of reading pressure/vacuum in other places as well, can anyone give me a simple explanation as to WHY it is measured like this?
Actually, I think I just figured it out myself. Anything BELOW 14.7 psi is technically "vacuum" and anything ABOVE is boost. So if my MAP is actually sitting at "5" psi, it's 10 PSI below the ambient atmospheric pressure. Doh. Then I guess that leads me down another path... how does the car figure out barometric pressure? I see a monitor, but where is the sensor?
Also I see a sensor on the cold side intercooler piping. What is it? Charge air temp sensor?
Last question: will intercooler/piping EVER see even a slight amount of vacuum? I know a leak in the IC piping won't result in a vacuum leak, or anything like that, because it's on the wrong side of the throttle body. And I know the vacuum inside of the intake manifold is caused by the restriction of the closed throttle plate, but on the turbo side of the throttle body, it would have to be under a very slight, nearly un-measurable level of vacuum unless the turbo provides no restriction (or is actually moving enough air) at idle.
Or am I wrong? Sorry, total newb with only basic level of understanding trying to learn a little more.
So the MAP sensor on the manifold. It's obviously post throttle, which at idle should be in vacuum. Right? However it shows like 5 psi on the Accessport. Looking at Cobb's site, I see the Boost Pressure monitor is "MAP minus barometric pressure" which is 14.7 psi... okay, so to me this doesn't make sense. If I were to put a hole in the manifold and stick my finger over the hole, I would feel it sucking my finger in.
I've run into this weird (at least in my head) way of reading pressure/vacuum in other places as well, can anyone give me a simple explanation as to WHY it is measured like this?
Actually, I think I just figured it out myself. Anything BELOW 14.7 psi is technically "vacuum" and anything ABOVE is boost. So if my MAP is actually sitting at "5" psi, it's 10 PSI below the ambient atmospheric pressure. Doh. Then I guess that leads me down another path... how does the car figure out barometric pressure? I see a monitor, but where is the sensor?
Also I see a sensor on the cold side intercooler piping. What is it? Charge air temp sensor?
Last question: will intercooler/piping EVER see even a slight amount of vacuum? I know a leak in the IC piping won't result in a vacuum leak, or anything like that, because it's on the wrong side of the throttle body. And I know the vacuum inside of the intake manifold is caused by the restriction of the closed throttle plate, but on the turbo side of the throttle body, it would have to be under a very slight, nearly un-measurable level of vacuum unless the turbo provides no restriction (or is actually moving enough air) at idle.
Or am I wrong? Sorry, total newb with only basic level of understanding trying to learn a little more.
