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Accuracy of OEM boost gauge?

Does anyone have any experience of how accurate their OEM boost gauge reads?

My OEM gauge has only ever shown a boost level of 0.5 bar, in the time that I have owned the car, so I'm trying to understand if I have a problem to fix. I have never driven or had a ride in another 930 so my seat of the pants boot gauge has had no calibration experience.
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Old 11-06-2008, 06:56 AM
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I have found mine to be very inaccurate.
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Old 11-06-2008, 08:28 AM
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Is the gauge you are talking about in the tach or replacing the clock?

In tach - worthless for anything except amusement

In clock position - dead nuts accurate

Of course, this is my opinion. YMMV
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Old 11-06-2008, 09:31 AM
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Zero to awful.

It's like the oil level gauge, something to fill space and cause confusion.

Very slow to react and not reliable. I don't know if it is the sending unit, the gauge itself or all of the above. It's a good reference as the inaccuracy is constant so it's useful to detect changes.

If you have time to read that small gauge while on boost, then it is probably a good indication that you indeed have boost problems!

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Old 11-06-2008, 10:29 AM
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Quote:
Originally Posted by jimmcc View Post
If you have time to read that small gauge while on boost, then it is probably a good indication that you indeed have boost problems!
I might indeed have a problem then! Time to make a plan. Thanks for the comments guys. (I am asking about the OEM gauge built into the tach)
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Last edited by boostfix; 11-07-2008 at 06:49 AM..
Old 11-07-2008, 06:28 AM
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Quote:
Originally Posted by jimmcc View Post
Zero to awful.

It's like the oil level gauge, something to fill space and cause confusion.
Agreed! The boost gauge within the tach seems to move with the slightest bit of engine breath!

As for the oil level gauge, mine is dead on accurate, and jives with what the stick says. Of course this assumes typical Porsche oil check procedures: car warmed up, level ground, engine idling, wait about 30 secs...blah, blah, yada, yada...

When it's cold, yeah, the level gauge no worky!
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Old 11-07-2008, 06:36 AM
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Quote:
Originally Posted by sand_man View Post
When it's cold, yeah, the level gauge no worky!
The manual states not to pay attention to the oil level gauge until the oil is warm, car is level, bla bla bla. I bought my car in Texas and dove it home to Atlanta in one shot, the next morning I took the car out to run an errand and freaked out when the oil level gauge was flat. I went home and checked the manual and I have used it as a rough guide ever since.

My factory boost gauge seemed more like an on off switch and with a 1 bar spring the information I really wanted to know was off the scale of the gauge. I replaced mine with and LCD system that I am happy with.
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Old 11-07-2008, 07:17 AM
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Does the boost level change depending on outside temp?

Mine gets/shows higher boost level during cooler weather, but the car feel the same.
Old 11-07-2008, 07:57 AM
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Totally inaccurate. Get yourself the VDO gage that mounts in the closck location. Much more accurate though probably still liable to +/-0.1 bar inaccuracy.
At least it will tell you vacuum unlike the tach gage.
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Old 11-07-2008, 08:40 AM
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Red face

That's good to know. Mine pegs 1 bar under full boost and I've been concerned that if it's on the high side, I may be in trouble. I have a tial 1 bar spring in there..... maybe I should install a .8 or so as a safety measure?
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Old 11-07-2008, 11:35 AM
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I recently installed the boost/vac gauge from NHS in the clock location (gets boost signal off of brake booster hose). My observation in comparing the two is that my tach gauge is reasonably accurate at telling me full boost level...But it reads very different from the mechanical gauge when the boost is building. For example, the tach gauge will show .2 bar while the mech gauge shows that manifold pressure is at atmosphere (0 bar) or even a slight vacuum. My understanding is that this difference is due to the fact that the mech gauge reads after the throttle plate, and the factory tach gauge sender is before the throttle plate. I do think that factory boost gauge sender in my car is not original (looks too shiny so must have been replaced at some point).
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Old 11-07-2008, 02:56 PM
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