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Ian:
I'd go with the air/fuel gauge before the volt meter, but....
Volt meters are nice because you can see the battery charge level and cranking voltage (how far it drops) during start up. So it's an indicator of battery/starter health. Plus, it shows (when the car's running) the charging voltage, thus giving you an indicator for if your alternator and voltage regulator are working correctly. Also nice to know.
EXCEPT... most of the time, that stuff works fine anyway, and if your battery's dying, you don't need a needle on a meter to tell you that. Plus, regular handheld voltmeters or electrical multimeters are easy to hook up when you're doing troubleshooting under the hood. What I'm suggesting is that voltage isn't something you need to monitor all the time, really. It's a "nice to know it's okay" kind of indication that you can really just check whenever you do tuneups or oil changes. (And I have a voltmeter in my gauge cluster, so I'm not saying they're bad!) But it's a charging system/battery health monitor, that's all.
An air/fuel gauge would be more useful, though again, with everything working properly in your well-tuned car, it just gives you a "status quo" sense of well-being. Doesn't really tell you anything useful unless something's broken, and then you're going to know anyway because the engine will be running funny, plugs will foul, smoke will come out, or something else probably obvious will happen. Both air/fuel and voltage gauges fall into the category of "troubleshooting gauges" rather than "driving gauges."
Let me explain "driving gauges." When you're piloting your vehicle, you need to monitor transient operating parameters that change over time -- a system's status at a glance. As far as you're concerned as a DRIVER, an idiot light is enough to tell you when something's wrong, if you don't know it instantly by feel. (As a MECHANIC, of course, you need to know more, but that's after you stop the car!) So driver's gauges: things like temperatures and pressures are good to know. Thus, Vac/Boost and oil pressure are "must-haves," and I agree with your decision to get those! The car already has a fuel gauge and coolant temperature gauge, which are other important status things to know about. So now to answer your question... if you can only get one more gauge, what should it be?
You might consider oil temperature as an easy one to put in. There are temperature sensing plugs which replace your oil drain plug, and with a turbo, having an indication of warm oil tells you when it's safe to start boosting. I often note (even here in Florida) that my water temperature will stabilize in the mid-green long before the oil temperature rises up off the peg, and I don't give my Beastie any serious throttle input until it has warm oil. Just playing it safe. (Actually, I'd REALLY like to be able to monitor the oil temperature as it flows out of the turbocharger bearing area! That would tell me how things were doing on the pre-shutoff cooldown. Oh, well.) Anyway, that might be something you'd like to know in your daily driving.
Something even more useful might be the air temperature coming out of your intercooler. If you do a lot of sustained boosting (hill climbing or repeated hard accels) the intercooler is going to get hot and need some time (it works like an air-cooled heatsink) to come back down to near-ambient temperature. So IC outlet temperature might be useful for you to monitor, depending on how you drive. If you're clever, you might even be able to use several sensors with a switchable gauge to read outside air temperature, IC outlet temperature and Delta T, the temperature DROP across the IC (outlet minus inlet.) These would be especially useful if you have any sort of modified IC -- either fan-cooled, water-spray cooled, or liquid (immersion) cooled -- because you'd see immediately what the heat removal efficiency was, instantaneous, sustained, and post-boost. The cooler the air charge, the more power you're going to have. (I'd want to know this stuff if I was boosting all the time, which I don't.)
I guess what I'm saying, from the test pilot perspective, is that your choice for that third gauge really depends on your own preferences and how you typically drive.
One thing I'd like to suggest, though, is that you put the Boost/Vac gauge where it's easiest to see. It's something you'll want to watch all the time, so don't mount it low in the dash behind the shifter or something. That's fine for "startup" or troubleshooting gauges, like the voltmeter, but not for the "driving" gauges. Put the boost gauge where it will fall into your primary instrument scan with the tach and speedometer, if you can.
Lastly, if you're having trouble deciding, why don't you leave the third gauge out for now? After you've driven the car with the turbo for a few weeks, it might suddenly occur to you what you want to monitor. It would be a shame to wish you had space for another gauge after you've already put in one you really don't use.
Cheers!
- = M = -
'87 900T (just hit 160K today!)
, Sat, 25 Nov 2000 21:30:42, Sun, 26 Nov 2000 11:13:16
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