I have just fitted a boost gauge for the first time and I just wanted to check that when I am driving at low revs (Out of the turbo) the gauge should be reading negative?

When the car is in the Turbo the boost pressure is positive as expected. (Will have a look and see what sort of boost it is hitting tomorrow!!)

In a nutshell ................Yes

If you have a re-map you should be around 15psi plus, then dropping back iirc

No boost should be showing as 0 surely? Negative is a vacuum?

Zero is atmospheric pressure anything above is boost or something like that................. I can't remember right now to be honest. Some one how knows will be along to explain I'm sure:confused:

It should defintely be showing vacuum (negative) when idling or off boost. But I don't know why!

Rob we've been here long enough to know why really. Should we be ashamed of ourselves............You especially:P:P

It should defintely be showing vacuum (negative) when idling or off boost. But I don't know why!

Think about what happens when you increase the volume of the air intake system by filling a cylinder with air but have the throttle valve partially closed.

Rob we've been here long enough to know why really. Should we be ashamed of ourselves............You especially:P:P

True!

Rob cant be held responsible for not knowing why as he has the big responsibility for hosting the picture that has shown every one where to plumb in the T piece

You're all correct; off-turbo, a 2-way boost gauge will read below atmospheric pressure (negative). This is because the air is flowing through a pipe, and when this happens, its pressure does drop as a result. If you want a better expn, run a web search for "gas dynamics".

Manifold vacuum - Wikipedia, the free encyclopedia

You're all correct; off-turbo, a 2-way boost gauge will read below atmospheric pressure (negative). This is because the air is flowing through a pipe, and when this happens, its pressure does drop as a result. If you want a better expn, run a web search for "gas dynamics".

Had a Google............I think I'll leave that to you Ken :confused::confused:

Manifold vacuum - Wikipedia, the free encyclopedia

Which led me to this,Turbocharger - Wikipedia, the free encyclopedia Which I find easier to understand

Knowing that it happens, and that the deeper the depression, the higher the throttle setting (off turbo on naturally aspirated cars only) is about all you need for practical purposes.

Knowing that it happens, and that the deeper the depression, the higher the throttle setting (off turbo on naturally aspirated cars only) is about all you need for practical purposes.

I love it when you get all technical Ken...............Cheers mate

Even though sometimes I have no idea what your on about

Just taken her out for a blast and I am seeing between 0.6 - 0.7bar of boost pressure...... Is this about right for an un-mapped car?

Also a big thanks to all of you for the info to allow me to fit it! (Especially Robs pictures!!)

Rob cant be held responsible for not knowing why as he has the big responsibility for hosting the picture that has shown every one where to plumb in the T piece

Also getting chatter from the Boost gauge !? Is this normal ? Can I get rid of it?

yup, you'll need a little filter to smooth the airflow on the pipe work connecting the boost gauge

Like a fuel filter?

yeah, but a very small one. The other way is to use a small screw clamp to squash the gauge pipework a little.

Automotive Dials Gauges pods t-piece

Click on T piece resrictor

Just taken her out for a blast and I am seeing between 0.6 - 0.7bar of boost pressure...... Is this about right for an un-mapped car?

Also a big thanks to all of you for the info to allow me to fit it! (Especially Robs pictures!!)

Yes this is correct for an un-mapped car (roughly 8-9 psi).

As for negative boost, mine used to be around 1 bar or -15psi when running the standard turbo on tickover/off boost.

Hope this helps.

Steve:)

Also getting chatter from the Boost gauge !? Is this normal ? Can I get rid of it?

You need to make a restriction in the pipe feeding the gauge, the further down the pipe away from the gauge the better. You only need a 0.5mm hole or so.