A Vacuum gauge is a very simple and safe piece of equipement to install in your car and as well as being a great tool for tuning can also be used to help with your driving style to achive a smoother and more economical way of driving.
There are a number of different designs of vacuum gauge available as shown in the pictures below, from a pure readout of vacuum in inches of mercury, to a colourful "performace meter" which gives an indication of the type of driving you are doing. Finaly there is an electricaly opeated gauge but with a readout in Bar. All of these types are availble with prices ranging from a few pounds to about 30 pounds.
To install a vacuum gauge a piece of plastic tube has to be attached to the inlet manifold. This can be done by removing the manifold and drilling a hole, then tapping it out and making a fixing so that the tube can be attached. This can be a bit of a chore but the manifold must be removed otherwise debrie from the drilling will find its way into the engine and cause lots of expensive trouble.
The way I did on my MGB GT was to remove one of the tapped bungs that are fitted to the manifold (these tapped bungs fill in holes when things like a brake servo is not fitted). I then drilled a hole through the bung the correct size to be tapped out to take a bleed nipple used for the brakes. Before I fitted the bleed nippled I cafully drilled out the interenals (so that it just hollow), this allowed the pipe to be fitttd easily. It was just a case of fitting the bung back into the manifold and running the plastic tube into the car to the place where the gauge is to be fitted.
Once installed and running it can be used to tune the car, use it to help with economical driving or just to have as an extra gauge in the car (you can never have enough gauges!)