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I have been looking at Autometer Boost Guages and reading up on gauge here and cant seem to find an answer to my question...

Do I want a 30-0-30 Vacuum/Boost Gauge or a 0-35 Boost Guage?

Why would I want a vacuume guage and what does that measure?

Thanks in advance...

It's really just a matter of preference really, both do the same thing.

However since you are not in boost all the time its neat to see the amount of vacuum too. Id get that one.

So what does the vacuum part measure? Vacuum of what?

Vacuum inside cylinder #1 (and in general, the engine). I got the vacuum/boost Autometer gage too -- works well.

The engine is either sucking air in, aka vacuum, or you are forcing it in with the turblow, aka boost.

To be technical the air is always being forced in, its just at 0 psi is atmospheric pressure and anything past is extra force from the turbo. Either gauge will be fine, but I would go with the one that shows vacuum unless you plan on running 35 psi

I'd recommend getting the 30 - 0 - 20 gage, unless you plan on making over 20 psi of boost. I routinely see ~25 vacuum (forget its measurement) when coasting in gear.

first off, go with the 30-0-20 gauge, it gives you a better idea of what your throttle input is doing and so on.

Second, if you happen to get the 30-0-20 gauge, the "0 psi" mark tells you that the turbo is pumping enough air to equalize that of what the engine would normally be sucking in. At this point the engine isn't really sucking air in, but the air isn't exactly being shoved in either.

30-0-20.

I have one and I like it. Like everyone's said, you see more with it this way. It's also fun to see a needle bounce around outside of boost.

Yep, 30-0-30 is the way to go. You need to know what your vacuum is as it will effect performance and idle.

I had the Autometer Phantom Series boost gauge and it worked flawlessly.

Okay so how much harder is it to install a 30-0-30? I heard that I need to mount another tube in another spot to read vacuum. Do I?

Nope, it uses the same single tube.
but make sure you pick a line off the intake manifold to tee into.

There should be a good one on the passenger side.

Don't tee into the bypass valve vacuum line, or you will get inaccurate vacuum readings.

I ended up teeing into the brake booster line.

or tap into the MAP line and read what the ecu is reading... pass side line coming off front most intake runner.

It will probably be a while before you are going to be running over 20psi.....I got a 30-0-30 by accident...and traded for the 30-0-20....which is a little more spread out and accurate in the 0-20 psi. The incraments are larger therefore giving you a better idea where you are at.

BSOD2600 wrote:I'd recommend getting the 30 - 0 - 20 gage, unless you plan on making over 20 psi of boost. I routinely see ~25 vacuum (forget its measurement) when coasting in gear.

i might be wrong but i think it's measured in millimeters of mercury or pascals.
not sure which though.



i have no clue why i know that lol.

Simple rule:

If your car is Gas...get a 30-0-20 or whatever


if Diesel:

0-40

The vacuum part of my gauge is more useful to me than the boost part...


and vacuum is measured in inches of mercury (InHg)

Vacuum can also be measured as a negative gauge pressure, so negative PSI values are accurate measurements. It's like measuring in feet, inches, meters, furlongs, leagues, clicks, etc. It's all the same thing .

30-0-20 would be the way to go.

inches of mercury. that's it lol. thanks.


i don't think you can have negative psi.
it seems impossible to me. to have negative pounds lol.

^^^ it's in the definition of gauge pressure. Trust me on this one, as a degreed aero engineer . Vacuum is really just a measurement of the positive pressure of the surroundings in comparison to your control volume.

Remember, science pushes and pulls but it never sucks .

skid542 wrote: Vacuum is really just a measurement of the positive pressure of the surroundings in comparison to your control volume.

Remember, science pushes and pulls but it never sucks .

Well said!


and LOL to the science thing

hahaha ok. i gotcha.