boost guage difference?!?!

[turbo98eclipse]

can somebody please explain to me wat the hell is da difference between a regular boost guage and a boost/vaccum guage?

 

[gigahz95]

If you knew anything about vacuum and atmospheric preasure....sigh

I'm partially retarded but 2in mercury is 1psi. So a quarter of the gauge will read up to 30in in vaccuum. And the other half will read up to 30psi. I think im right?

 

[turbo98eclipse]

ok so do i reely need 2kno how much vaccum is being created or is it just 1of those guages u get 2 say u got a guage?

 

[gigahz95]

Mine reads vacuum and psi, and so do the people i know with turbo cars that have gauges. I dont think they're anymore expensive than a gauge that only reads boost, and they hook up the same way. So it should be in your best interest to get the combo gauge(not a combo, just a different face) for the best reading on the engine.


tldr: get the gauge that shows vacuum, they're better.

 

[turbo98eclipse]

iight thanx man

 

[Diplomat]

Let me see if I can make this easy for ya.

When a normally aspirated motor is running, the air from the filter all the way into the intake manifold is under a vacuum. When I say "vacuum" I mean the pressure in the manifold is lower than the outside [atmospheric] pressure, of course. So air is being "sucked" into the engine from the piston moving on a downstroke. How much of a vacuum is created depends on a few factors like engine speed. Fifth grade science, right?

When you throw a turbo into the mix, things change a bit. At idle, you're still going to have that vacuum. Even though the turbo is spinning at idle, it's not moving much air. So the air inside the manifold is still a lower pressure than normal outside pressure. At this point, our vacuum/boost gauge is still going to read below zero, or in the vacuum range. However, as the turbo begins spinning faster (with engine speed) air is now being both "sucked" into the engine by the piston as well as being "pushed" by the turbo. Eventually the turbo will be moving (pushing) enough air into the engine that intake manifold pressure and outside air pressure are the same (equal). This is when our vacuum/boost gauge reads zero. As you give it more gas, the turbo spins even faster and the air in the manifold is becoming pressurized. Hallelujah! Now we're making boost! Life begins here.

When the engine is not running, no air is being sucked in, so the air in the manifold and the air outside will even out or return to zero pressure. This doesn't mean outside air pressure is zero. That would make it challenging to breathe. Rather it means that you're not under vacuum or boost. Aiight?

The stock boost gauge would be an example of a vacuum/boost gauge... if it actually measured vacuum/boost.

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...and of course a boost gauge measures only that pressure above zero. Because no one cares about what happens in life while not under boost.

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Which one is right for you? It really just depends on how much tuning you intend to do.

 

[gigahz95]

Thats correct. Only "boost" gauges half of its in mercury and half is in psi for the sake of an easy "zero" point. If you wanted to be a badass like some people i know you could get a duel needle gauge that reads only in mercury and do the conversion in ur head. The zero point would be some relation to hg and atmospheric pressure for u area. O god im getting confused

I'm not smart enough for this crap