Hello all,

I have an 88 turbo 2 with about 74,000 miles. It looks runs and drives like new.
Its an impressive car. I dont have any real probs with it, only a question or two.

Im wondering why the stock boost gauge reads -20, zero, and then 40 max...

How can there be minus boost ? Im thinking there is either boost, zero, or I have boost about 1-5.

The needle sits at -20 boost, or level, when driving and boost not applied,etc

Is there some scientific principle that they call a no boost situation , - 20 ?

thanks all

MACK

 

negative boost= vacuum.

The stock gauge is inaccurate, plus i cant understand that type of measurement anyways. Just buy a aftermarket boost gauge.

 

The guage reads pressure. The intake draws a vacuum until the turbo spools up enough that the pressure becomes positive, and the guage reflects that.

 

all engines have vacuum, you dont make boost until you have enough exhaust flowing to push the turbine wheel. so no boost until more load on engine

 

The gauge isn't actually a "boost" gauge, it's a manifold pressure gauge. When the engine's not running, the pressure in the manifold is equal to atmospheric, or zero gauge pressure. When the engine is sucking harder than the turbo is blowing, the manifold pressure drops below zero gauge pressure (vacuum). When the turbo is blowing harder than the engine is sucking, the manifold pressure rises above zero gauge pressure (boost).

The gauge is calibrated in tens of millimetres of mercury (x10mmHg), so "-20" means -200mmHg. In cruise and decel conditions manifold pressure is actually lower than that (around -250mmHg at cruise, and down to -500mmHg during decel), which is which the gauge only rises above -20 during acceleration.

1psi = 52mmHg, so the stock gauge reads from -3.8psi to +7.7psi.