Turbos for Dummies

[Banger]

Hey all. Don't flame me for asking, but can someone explain the turbo boost gauge to me? While I've had several high performance engines in the past, they've all been either naturally aspirated or supercharged. I'm familiar with boost gauge on a supercharger, but what's with this turbo gauge? It looks like the top center of the gauge is zero, and the dial can rotate either CW or CCW. But in either direction the numbers increase. What gives? Thanks in advance!!!

 

[Cautionary Tale]

vacuum and boost its the way turbines are powered, when out of vacuum boost builds until set pressure and away you go.

You can also can think of it as negative and positive pressures

 

[gram10]

Engines are air pumps, the boost gauge reads the pressure in the intale manifold relative to the atmospheric pressure. When the gauge is negative, the engine is pulling a vacuum in the intake manifold relative to the outside air pressure. That's why it shows negative value for pressure compared to putside. The vacuum is measure in in Hg (mercury) it switches to psi when the turbos start producing boost. 1 in Hg is about 0.5 psi, they switch between the 2 types of measurement so the scale on the gauge looks good/is readable when in vacuum. Otherwise, in our trucks you'd be seeing 28 psi on onside and between -1 and -2 psi when in vacuum.

Easy way to think about it, on a naturally aspirated engine, when you floor it, the throttle is completely open, the boost gauge in this situation would show 0 since there pressure outside the intake manifold and inside the intake manifold should now theoretically be the same. Add a turbo, or supercharged, and now you'll see a positive boost pressure value.

 

[Cautionary Tale]

Engines are air pumps, the boost gauge reads the pressure in the intale manifold relative to the atmospheric pressure. When the gauge is negative, the engine is pulling a vacuum in the intake manifold relative to the outside air pressure. That's why it shows negative value for pressure compared to putside. The vacuum is measure in in Hg (mercury) it switches to psi when the turbos start producing boost. 1 in Hg is about 0.5 psi, they switch between the 2 types of measurement so the scale on the gauge looks good/is readable when in vacuum. Otherwise, in our trucks you'd be seeing 28 psi on onside and between -1 and -2 psi when in vacuum.

Easy way to think about it, on a naturally aspirated engine, when you floor it, the throttle is completely open, the boost gauge in this situation would show 0 since there pressure outside the intake manifold and inside the intake manifold should now theoretically be the same. Add a turbo, or supercharged, and now you'll see a positive boost pressure value.

Fine explanation but if that's your "for dummies" explanation, I'd love to read the Tolstoy level novel that would be "detailed explanation"