catflap

is this ok, when driving it does what i expect (17psi on WOT) 0 psi on light, its the -20 at idle ?? that ok

ktulu

yep

whip

There's vacuum in the manifold when the throttle's shut, I believe. So it would appear to be ok m8.

Whip

john banks

I believe it is physically impossible to be at lower than -14.7 PSI unless you are living below sea level or the air pressure is particularly high. Complete vacuum would be -1 atmosphere relative pressure.

I find -20 to be an error.

ktulu

mine shows same readingd on my98, infact i believe ive seen lower

the rest of the boost readings show as expected

if there is a problem it is one without symptons, so far?

john banks

Well you can't have less pressure than no absolute pressure = total vacuum = -1 atmosphere relative (which is how a boost gauge usually reads). The gauge is in error if it reads under -15 in normal circumstances.

catflap

John is right
but its at -20 at tick over (in vacume) sets at -1 when engin off

dowser

Think you'll find scale changes for negative values

Richard

ktulu

its the same scale.

catflap, I get exactly the same as you -20/-25 tickover, as soon as throttle touched up to about -1.

autometer gauge?

I dont think there is a problem?, what readings are everyone else seeing?

GavinP

On my Autometer gauge I get -20/-22

I think the air filter/intake does have an impact - I added a bellmouth to the end of the 80mm air ducting on my car and the vacuum has reduced from -25 at idle.

Thanks

Gavin

john banks

So what's that all about then? Is it reading in PSI? How can you have more vacuum than a complete vacuum? Sorry to be a turd but I just don't get it.

ktulu

John,
Must admit, I dont get it either!, but it does seem to be the norm for autometer gauges?

I assume this is not the same on your gauges?, what gauges have you got? (not that that should make a difference?)

Im sure someone can shed some light on the subject.

J

SPEN555

My Autometer gauge reads -20 don't know whether the vacuum is in PSi though.

Damian.

GavinP

The vacuum on my gauge is marked as upto 30 "In. Hg" which I think is "inches of mercury" ?

Thanks

Gavin

GavinP

Apparently multiplying the "In. Hg" x 0.4912 gives psi...

So -20 In Hg would be about -10psi if I understand correctly...

Thanks

Gavin

john banks

That explains it then. What sort of idiot would put a different scale on for vacuum compared to boost? As some women would say, "Obviously a man did that". I know some of the EBCs do this too. Very odd.

Mine is in PSI and reads about -8 at idle from memory.

Orwella

I thought normal atmospheric pressure on this plannet was around 14psi. Guages measure from zero to make things less complicated for us, so if it shows -10psi there is actually positive pressure (4psi) but becase we have a denser atmosphere it counts as negative relative pressure.

My physics classes were a long time ago but I think it goes something like that.

slippyr4

No ****!!! of course there's a vacuum.

It's not all that clever to pull the pipe off as a general rule cos you're sucking unfiltered air into your engine. Admittedly not much of it though.

whip

LOL @ Catflap

Whip

dowser

NA engines have their air pulled into engine & with forced induction it's pushed into engine.....when you're on boost. Prior to that there'll always be a vacuum.

The different scale is necessary - imagine getting, say, 1 bar of negative manifold pressure. The engine would stall well before this.

The gauge can actually be used to tune your inlet system to remove restrictions - try placing a piece of cloth over your air filter...you'll see the gauge go off the scale. Less is better

Richard

Moles Dad

Minus .64cm/kg at (hot) idle as shown on HKS evc iv.

Dont mean a lot to me, I only take an interest @ 000 and above

Cheers all, MD.

catflap

It is deff a vacume, i removed the gauge and started the engin and it sucks, sucks pretty hard in fact, lol my mate stuck it to his cheek and shouted "LOOK RY, IM IN THE MATRIX" as the pipe stuck to his cheek.

But there is a definate vacume there(at tick over)

[Edited by catflap - 4/5/2002 4:28:06 PM]