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Question Need Some Advice Maybe Consensus

Dear Fellow Turbo Aficionados,
Since no one answered my request to obtain the proper tachometer for my car (I have newer 993-641-332-00 tach w/ OBC and I need an older 965-641-322-01 tach w/ OBC and boost indication), and I don't know how much boost I am running, I am going to try something else.

I will install an electronic or mechanical VDO boost or vacuum/boost gauge. The question is where to plumb the source. I realize that if I get just the boost gauge, I can plumb it into an existing rubber hose with a plastic "T" almost anywhere after the turbo outlet, IC, BOV, throttle body, or intake manifold. But what is the best location that also is convenient?

If I go with the vacuum/boost gauge I have to plumb it in past/below the throttle plate to see the vacuum, right? I think there are at least seven places I could go. Is there a consensus which is the best place for the most accurate reading?

How does the group feel about mechanical vs electronic? I can do either. My sense it that you lose some of the accuracy with the mechanical since the run is so long (~10'?) and the air is a little springy.

Thanks for chiming in,
Mark
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1991 964 Polar Silver Metallic Turbo Coupe
Old 03-01-2008, 07:25 AM
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Mark- if you look at some of my posts you'll find that I'm generally mechanically challenged and I'm learning a lot about my 930 and cars in general- at the expense of the patient folks on this forum. Can't really offer much in the way of options for vacuum sources- but I recently removed my clock and installed a 934 style boost gauge that NHS modified for me so that it shows vacuum as well. Per their instructions I tapped into the rear of the brake master cylinder. The kit included hose to the gauge and a new vacuum fitting with a "t" to allow for both vacuum to the master cylinder and the gauge. The hose kit is available from Performance Products and Pelican as well. If you were to order the kit (about $65) you'd see that it's a pretty basic install. As far as other areas where one can tap into for vacuum I'm sure some of the smarter guys will chime in with their expertise- but there's got to be a vacuum port on the master of a 964 turbo so I'm thinking it's the same sort of setup. Take a look at the picture below and see if you think it might work for you. Good luck with your project.


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Last edited by jay71; 03-01-2008 at 08:26 AM..
Old 03-01-2008, 08:16 AM
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That's the best way to do it.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

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Old 03-01-2008, 11:33 AM
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That's the easiest way to do it on a pre-964 car but I'm afraid 964 turbos have hydraulic brake boosters. There is no boost/vacuum source near the front of the car that I'm aware of.

You'll most likely have to run a small hose. Autometer makes a small plastic hose kit that works well. You can run it along the throttle cable and into the center tunnel. It'd be nice to put a coupling near where the throttle cable conduit connects. This would make it easier to remove engine/trans without cutting/splicing the hose later.

BTW, On the older cars I've used an early 944 brake booster ck valve that has that nipple made on to it. You can use an old early CIS(non-turbo) plastic fuel line to screw onto the back of the Clock style boost gauge that gives you a barbed fitting. Then all you need is some hose...

just an idea for those that get their rocks off scrounging around...
Old 03-01-2008, 12:40 PM
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Why not get your 993 tacho fitted with C2Turbo's PLX boost indicator?
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Old 03-01-2008, 01:06 PM
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Thumbs up Advice and Concensus

Thanks to all that responded. My 964 turbo does indeed have the electric boosted brakes that do not run off engine vacuum. I know I have to run the line back to the engine now. But I still don't know where I am going to get my signal for the PLX Boost Indicator. If the instructions tell me then I'm home free and I will report back to the forum where I tapped into the induction path.

Hey,
Why didn't I think of modifying my 993 tachometer with the PLX Boost Indicator? That would solve both of my problems at once and I wouldn't have to hack into a 964 tachometer!

Now, how do I get one of these beauties?



Thanks,
Mark
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Old 03-03-2008, 07:28 PM
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Quote:
Originally Posted by lucittm View Post
Thanks to all that responded. My 964 turbo does indeed have the electric boosted brakes that do not run off engine vacuum. I know I have to run the line back to the engine now. But I still don't know where I am going to get my signal for the PLX Boost Indicator. If the instructions tell me then I'm home free and I will report back to the forum where I tapped into the induction path.

Hey,
Why didn't I think of modifying my 993 tachometer with the PLX Boost Indicator? That would solve both of my problems at once and I wouldn't have to hack into a 964 tachometer!

Now, how do I get one of these beauties?



Thanks,
Mark
Hmm,
I think the factory tapped into the Intercooler. I have a gauge tapped into the intercooler and one tapped into the brake line.

The IC tap is in "Front" of the Throttle Body, and the Brake line tap is behind the throttle body.

If you tap into the Intake manifold or at the base of the Throttle Body you will have a reading closer to what your intake valves are actually seeing in reference to Boost.

So here is what I "see" when my car is starting to boost.

First the IC tap shows boost coming on, and depending on what gear I am in, I may "see" .5 Bar before the Tap in the brake line starts to move. Now when the IC tap is indicating boost, and the Brake line tap shows no Boost, I can tell by the seat of the pants dyno, that boost is "starting to Happen.

When the Brake line tap shows boost, there is no doubt how the car feels, it is definitely positive pressure in the manifold.

I don't think you can go wrong in either location. Most likely, the tap below the throttle body is more accurate.

The only other thing to consider is that the control line for your Wastegate is coming off the Intercooler. So that's basically the "POP Off" pressure for boost, and it is being referenced off the IC body. So maybe that's where you should read boost.

There's a great Video on the Forum by JIM2 that shows his aircraft dual manifold gauge while he's hauling Azz on a racetrack. It shows what is going on if you have a gauge that shows two taps, one below and one above the throttle body. It is very interesting to watch, especially if you are trying to figure out where to plumb you Boost Gauge.

Check out his video here. Watch the two needled gauge in the Clock position. I just bought one of these and will put in place during my next go round.

http://www.youtube.com/watch?v=pKECPR4RjmM
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---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 03-03-2008, 08:40 PM
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