You can use the vacuum gauge on your car, its just not very applicable under any boost. Vacuum gauges are very helpful if you know how to read them. While tuning, they can be used to help set timing, idle mixture, idle speed, and other things. They can help diagnose cracked rings, faulty valves, vacuum leaks, and blown head gaskets. During driving, they offer a relative fuel economy indication. The more vacuum, the less fuel the engine uses in general. Some cars from the 70s and 80s had vacuum gauges that were calibrated for MPGs (only representative) so the driver had a visual representation. It was believed that watching the gauge peg might make some drivers back off on the pedal.
If you install the gauge on your car, select a vacuum source anywhere in the intake plenum. That's the common air box that is after the throttle body and before the individual intake runners. There should be at least one vacuum tube that you can tee from. It will frequently peg itself since under any boost it will register zero. It might pull the needle below zero depending on how the gauge is constructed.
Make sure you use good connectors. Using normal vacuum tees might not do so well at 6 psi positive pressure. If you blow one off, it will just create a leak, but it might be frustrating having to lift the hood after every time your foot hits the floor.
In your case, there is little use for the vacuum-only gauge. Since your intake vacuum is almost always affected by the little pressure changes in the compressor, its not very indicative of MPG. I would hold out for a boost/pressure gauge.
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11-27-2004, 07:21 PM
