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Wer bremst verliert
Join Date: Jan 2005
Location: Toronto, Ontario
Posts: 4,767
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Boost/vacuum gauge & sensor recommendation
I am finishing up my first supercharging project, in addition to the ECU logging/having to look at the laptop while I drive I'd like to have a boost gauge on the dash/rollbar.
I am going to run 14-18 lbs of boost. I have a 3-bar MSD MAP sensor. The supercharger is an Autorotor 417 positive displacement twin-rotor. Firstly, what range of gauge do I need? Is both vacuum necessary or will the engine always run in positive atmospheric pressure? My guess is if, as the gauge recalibrates at startup, it will show vacuum at times during idle, but increasing to boost as the supercharger spins up? I have read and been told the engine still runs at a vacuum, which is why brake boosters and other things running off vacuum Second, is an electronic or mechanical version the preference for a must-be-reliable environment? My ECU can put out a variable, configurable signal (as passed on from the MAP sensor to a gauge) so I believe I can adjust it to drive most electronic boost gauges. Or perhaps I can splice the MSD sensor to send the same signal to both the ECU (for its fuel and spark calcs) and to the gauge? I would think since both are voltage-driven sharing the same signal wouldnt' cause a problem? MSD has these: ![]() Looks like a decent broad-range, electronic gauge although no information is given on its instruction about calibration. Here are some more... Autometer 3659 ![]() VDO Mechanical 0-30 gauge ![]() Stewart Warner Mechanical Help with the range I need and recommendations of electric vs mech are much appreciated.
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2007 911 Turbo - Not a toy 1985 911 Cab - Wife's toy 1982 911 3.2 Indiash Rot Track Supercharged track toy 1978 911 3.0 Lichtbau toy "Gretchen" 1971 911 Targa S backroad toy |
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Blackbird Pilot
Join Date: Jul 2007
Location: The OC
Posts: 2,112
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I went with one from North Holleywood speedo and depending on cams and timing you might need more vacuum reading. I went with the -.5 bar to 1.5 bar guage (around $220) and am happy with looks and its reputation of how it performs.
You definately want a guage that shows the -vacuum so if you get a leak you'll know about it. I run a mechanical gauge and have been told its the way to go. Here's a pic of mine: ![]()
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Reaper | The Outlaw 930 Hotrod Gruppe Fünf Gruppen.com | The Baddest 934/5 Parts for the 911/930 D-Zug.us |
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resident samsquamch
Join Date: Oct 2005
Location: Cooterville, Cackalacky
Posts: 6,815
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I've got the "old skool" boost gauge with extra the tattle tale needle (tattle tale no longer works), but I've been thinking about sending it to NHS to have them refurbish it...I wonder if they could calibrate it to show vacuum?
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-jeff back in the saddle: '95 993 - just another black C2 *SOLD*: '87 930 GP White - heroin would have been a cheaper addiction... "Ladies and Gentlemen, from Boston Massachusetts, we are Morphine, at your service..." - Mark Sandman (RIP ![]() |
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Registered
Join Date: Feb 2008
Location: Marietta GA
Posts: 2,560
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Boost
![]() Boost + AFR ![]() |
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Blackbird Pilot
Join Date: Jul 2007
Location: The OC
Posts: 2,112
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Nice setup, like the color
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Reaper | The Outlaw 930 Hotrod Gruppe Fünf Gruppen.com | The Baddest 934/5 Parts for the 911/930 D-Zug.us |
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Crotchety Old Bastard
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Vac gage is manditory for tuning and for continual monitoring of the state of tune.
Love the LED gage in the tack.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds '78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8 |
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Wer bremst verliert
Join Date: Jan 2005
Location: Toronto, Ontario
Posts: 4,767
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Thanks guys.
So to be very specific, will a supercharged engine running at 14 lbs boost ever be running at vacuum? My primary goal is to have an indicator on the dash to indicate a problem with the motor while on the track. All the tuning is accomplished through dyno sessions and logging of ~20 variables. The gauge is more of a warning system on the track to know when there is a problem. Also, any other comments on mechanical vs electric? The brake booster hose passes right under the dash so it seems that would be a convenient source to tap into for a mechanical gauge. Interested if there is an appreciable difference in accuracy and reliability between mechanical and electrical.
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2007 911 Turbo - Not a toy 1985 911 Cab - Wife's toy 1982 911 3.2 Indiash Rot Track Supercharged track toy 1978 911 3.0 Lichtbau toy "Gretchen" 1971 911 Targa S backroad toy |
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Smart quod bastardus
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Mechanical gages are more accurate than electric.
You need to make sure you tap into the intake manifold after the throttle body to pick up vacuum and boost as the valves see it. Upstream of the throttle body you will see no vacuum. Brake booster is good spot.
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, full bay intercooler, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.95 bar max ---"When you're racing it's life! Anything else either before or after, is just waiting" |
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Metal Guru
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Brian, please explain.
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Paul B. '91 964 3.3 Turbo Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, H&R Coilovers, ESB spring plates- 210 lb |
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