What is a 'boost' gauge?

A 'boost' gauge is a pressure gauge that measures pressure (and, usually, vacuum) at the intake manifold. Ordinary vehicles only ever have vacuum at this location, as the engine attempts to suck in air. Turbocharged and supercharged vehicles pressurize the intake manifold by pushing in extra air. The intake pressure is referred to as 'boost'.

It is essential to have a boost gauge prior to modifying the turbocharger system on a turbo DSM. If the turbo is not set up correctly, it will push in more air than the engine can handle. This usually leads to a 'lean' condition - too much air, not enough fuel - which directly results in excessively high combustion temperatures and severe engine damage. For this reason, a boost gauge is always at the top of any DSM modifications list.

Non-turbo DSMs, having no turbo, have no need for a boost gauge. However, it is essential if the car is retrofitted with a turbo or supercharger system.