12 Quart ATF Fluid Change, Add Temperature Gauge and Remote Cooler

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2021Navigator

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Another detailed post! Too bad no one makes a wireless gauge as it seemed like there was a significant effort in mounting the temp gauge and routing its wires.

Have you ever heard of a ScanGauge:

» ScanGauge II

It lists 2 parameters:

MAP
BST
Manifold Absolute Pressure
Boost

Do you know how they would relate to the turbo boost pressures?
 

Indy

Member
47
27
18
Oklahoma
Too bad no one makes a wireless gauge as it seemed like there was a significant effort in mounting the temp gauge and routing its wires.
You would still have to run a power wire. It's probably possible to send power thru the air, but not for us common folks.

Have you ever heard of a ScanGauge:
No, but can't say I'm surprised thou. It does look interesting !

It lists 2 parameters:

MAP
BST
Manifold Absolute Pressure
Boost

Do you know how they would relate to the turbo boost pressures?
Zero gauge pressure starts at atmospheric pressure or what's considered 14.7 psi at sea level. Where absolute pressure at sea level would be 14.7 psi. Now atmospheric pressure varies and is not always 14.7 psi at sea level, nor is it always the same value on top of Pikes Peak.

Boost pressure is the amount of pressure above atmospheric pressure. A turbo charger takes what pressure is available (atmospheric) and compresses it (Boost). A turbo charger would be useless in a vacuum or 0 psi, there would be nothing to compress.

Hope that helps !

FP04_AbsolutePressVsGaugePress.jpg
 

2021Navigator

Member
95
42
18
Good point about needing to power the gauge!

So if you had a ScanGauge and your coasting down the road with very little throttle your manifold absolute pressure may read just a few psi above 14.7, something like 16.0 psi and the boost might read 0.0 psi. But then if you quickly gave it half throttle the manifold might read 25.0 psi and the boost would be 9.0 psi?

There are 2 turbos on our 3.5L, and I assume each one feeds 3 cylinders so there are 2 manifolds? So I guess the scangauge would show you the average of the two manifolds and two turbo boosts?
 

Indy

Member
47
27
18
Oklahoma
So if you had a ScanGauge and your coasting down the road with very little throttle your manifold absolute pressure may read just a few psi above 14.7, something like 16.0 psi and the boost might read 0.0 psi.
If the throttle plates are almost closed, then the engine is trying to pump more air than is coming in. Therefore you would be pulling a vacuum in the manifold or there would be less than 14.7 psi. Think about about trying to drink a thick milkshake thru a straw and you are the engine trying to pull thru that straw. Inside the straw is a lower pressure than outside the straw. That's why it collapses some times.

But then if you quickly gave it half throttle the manifold might read 25.0 psi and the boost would be 9.0 psi?
So every time we say 14.7 psi, we are also saying that is the atmospheric pressure for that time and place. It could be something entirely different the next day.

Both your numbers cannot be correct at the same time. Let's assume that the MAP is correct and it's 25 psi. Then the boost would be = 25 - 14.7 = 10.3 psi.

Now let's assume that the boost is correct and it's 9.0 psi.
Then the MAP = 9 + 14.7 = 23.7 psi


So I guess the scangauge would show you the average of the two manifolds and two turbo boosts?
That one I can't answer, I'm not familar with how your system is designed.
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