I remember having one of these gadgets on a 55 Chev i had from 1978-1980. I found it mostly useless because all it does is remind you of the really sad gas mileage you are getting. I never really understood the point in these things because it is impossible to drive in the "Good gas mileage" zone in the real world. I suppose it was just a gadget for looks and not much of anything else.
-- Edited by long stroke on Tuesday 2nd of October 2018 05:05:40 PM
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1957 Pontiac Pathfinder Deluxe sedan restored 261 six
1974 Chevrolet Caprice Estate wagon low mileage original 400 V-8
While these gauges were labeled for power and economy a vacuum gauge can be an excellent tool in letting you know the condition of the engine as well:
Engine Performance Testing with a Vacuum Gauge
A vacuum gauge shows the difference between outside atmospheric pressure and the amount of vacuum present in the intake manifold. The pistons in the engine serve as suction pumps and the amount of vacuum they create is affected by the related actions of:
Pistons rings
Valve train
Ignition system
Fuel control system
Other parts affecting the combustion process, like emissions devices
Each of these has a characteristic effect on vacuum and you have to judge their performance as compared to what is considered "normal". To do this, it's important to judge engine performance by the general location and action of the vacuum gauge needle, rather than just by a vacuum reading. What follows is a list of the kinds of gauge readings you may find.
Normal Engine Operation
At idling speed, an engine at sea level should show a steady vacuum reading between 14 in. and 22 in. Hg. A quick opening and closing of the throttle should cause the vacuum to drop below 5 in., then rebound to 23 in. or more.
General Ignition Trouble or Sticking Valves
With the engine at idle, the continued fluctuation of 1 to 2 inches may indicate an ignition problem. You should check things like spark-plug gap, primary ignition circuit, high-tension cables, distributor cap or ignition coil. Fluctuations of 3 to 4 inches may point to sticking valves.
Intake System Leakage, Valve Timing or Low Compression
A vacuum reading at idle that is much lower than normal might indicate leakage through the intake manifold gaskets, manifold to carburetor gaskets, vacuum brake booster or the vacuum modulator. Low readings could also be caused by very late valve timing or worn piston rings.
Exhaust Back Pressure
Starting with the engine at idle, slowly increase engine speed to 3,000 rpm. Engine vacuum should be equal to or higher than vacuum at curb idle. If vacuum decreases at higher rpm, an excessive amount of back pressure is probably present due to a restriction in the exhaust system.
Cylinder Head Gasket Leakage
With the engine at idle, the vacuum gauge pointer will drop sharply every time the leak occurs. The drop will be from the steady reading shown by the pointer to a reading of 10 in. to 12 in. Hg. or less. If the leak is between two cylinders, the drop will be much greater. You can determine the location of the leak by doing a compression test.
Remember, engine problems can affect transmission performance. If you suspect an engine problem, connect a vacuum gauge to the intake manifold. Note the location and action of the vacuum gauge needle, and use that information to determine the engine problem. Correct the engine problem before doing extensive calibration work on the transmission.
Ray, the vacuum gauge you are showing is for testing purposes only. That one is a must for anyone who works on his own car. The dash mount gauge was intended to aid in more economical driving practise. In reality it is impossible to drive in the economical mode unless you are parked. I had that gauge in my 55 Chev for a year and then threw it in the garbage. It was just an item to make your car look more impressive but useless. Do not confuse the two different gauges. Cheers.
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1957 Pontiac Pathfinder Deluxe sedan restored 261 six
1974 Chevrolet Caprice Estate wagon low mileage original 400 V-8
Ray, the vacuum gauge you are showing is for testing purposes only. That one is a must for anyone who works on his own car. The dash mount gauge was intended to aid in more economical driving practise. In reality it is impossible to drive in the economical mode unless you are parked. I had that gauge in my 55 Chev for a year and then threw it in the garbage. It was just an item to make your car look more impressive but useless. Do not confuse the two different gauges. Cheers.
Agree.
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Prince Edward Island
'64 Parisienne CS "barn find" - last on the road in '86 ... Owner Protection Plan booklet, original paint, original near-mint aqua interior, original aqua GM floor mats, original 283, factory posi, and original rust.
63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. 1963- Pontiac top selling car in Canada
Mahone Bay, NS Still not old enough to need an automatic
