What does your boost gauge read at idle?

[edh]

I asked this before - maybe i was a bit cryptic as I didn't get too many replies. Before i go looking for leaks again, I thought I'd ask.

Mine sits at about 0.4 to 0.5 on the factory gauge - also checked with a separate boost gauge plumbed in to the intake manifold.

Before the recent headgasket job, I seem to remember it was showing a much lower reading & was basically at zero.
I know the std boost gauge is a bit dodgy - may be a connection fault somewhere, so it might not have been accurate before.

Thanks

Ed

 

[Riverside]

Mine reads 0.4 at idle as you describe, and 1 (straight up) when the ignition is on but the engine is off.

Never seen it go below minimum (0.4)

hth

 

[John Sims]

I'm assuming by 0.4 to 0.5 you mean -.06 bar to -.05 bar atmospheric. This sounds pretty fair to me. I think you must have had a dodgy connection if it was reading -1 bar previously, that is a massive amount of vacuum for the engine to overcome at idle.

(1 bar on the dash gauge is atmospheric pressure)

 

[edh]

John

I was just quoting straight from the gauge (trying not to confuse anyone [] )

I can move the pointer on the boost gauge by flexing the dash - that's why I suspect the connection is a bit intermittent []

I do see the gauge drop lower at very light throttle openings - cruising on the motorway for example. It's way off the bottom of the scale then.

 

[924nutter]

ORIGINAL: John Sims

I'm assuming by 0.4 to 0.5 you mean -.06 bar to -.05 bar atmospheric. This sounds pretty fair to me. I think you must have had a dodgy connection if it was reading -1 bar previously, that is a massive amount of vacuum for the engine to overcome at idle.

(1 bar on the dash gauge is atmospheric pressure)

I am sorry but I beg to disagree, slightly.

The net manifold pressure, which the boost gauge reads can never go into the negative. As you rightly say, I think you even pointed this out to me, One bar is atmospheric pressure, i.e. 14.5 psi. When compared to the theoretical 0 psi at the inlet of a perfect vacuum pump, or internal combustion engine sucking through a closed butterfly 0.5 bar simply means that the air is at 7 psi net, or half atmospheric pressure or half a perfect vacuum which is 15 inches of murcury. With the vacuum bleed for the brake servo having an effect on the vacuum in the maniflod I would have thought 0.4 is quite good for an engine with some miles on it, but as the gentleman's post says, it was even lower, so maybe there is a slight leak. The important thing is what is its maximum reading? 2.2 bar is equivalent to 1.2 bar of boost. Any scientists out there?

edited for whoopsie.

 

[edh]

As long as this is normal behaviour at idle I'm not too worried about the detail...

My car maxes out the factory gauge - and made approx. 1.2 bar @ Weltmeister last year. We'll see how it gets on at this year's event.

 

[Guest]

mine reads 1 all the time (guessing it completely disconnected somewhere??)

 

[John Sims]

ORIGINAL: 924nutter

ORIGINAL: John Sims

I'm assuming by 0.4 to 0.5 you mean -.06 bar to -.05 bar atmospheric. This sounds pretty fair to me. I think you must have had a dodgy connection if it was reading -1 bar previously, that is a massive amount of vacuum for the engine to overcome at idle.

(1 bar on the dash gauge is atmospheric pressure)

I am sorry but I beg to disagree, slightly.

The net manifold pressure, which the boost gauge reads can never go into the negative. As you rightly say, I think you even pointed this out to me, One bar is atmospheric pressure, i.e. 14.5 psi. When compared to the theoretical 0 psi at the inlet of a perfect vacuum pump, or internal combustion engine sucking through a closed butterfly 0.5 bar simply means that the air is at 7 psi net, or half atmospheric pressure or half a perfect vacuum which is 15 inches of murcury. With the vacuum bleed for the brake servo having an effect on the vacuum in the maniflod I would have thought 0.4 is quite good for an engine with some miles on it, but as the gentleman's post says, it was even lower, so maybe there is a slight leak. The important thing is what is its maximum reading? 2.2 bar is equivalent to 1.2 psi of boost. Any scientists out there?

Granted my decimal points ended up in font of the zero's not between (very naughty) but I did say (or mean to say) -0.5 bar atmospheric. On my after market boost gauge it reads atmospheric as 0 and a positive manifold pressure (boost) there after. Vacuum is measured from -1 to 0 bar on the boost gauge

If I have 1 bar of boost it reads 1 on my boost gauge and 2 on the dash gauge.

At the end of the day we are saying the same thing but as we tend to talk about boost on Turbos (0.8 bar boost) I find it easier to read my Boost gauge the way it is written.