TOOTH GP-RIPPER 9J1641 - Caterpillar

Engine "boost" or manifold pressure is the difference in pressure between the air in the inlet manifold and the atmospheric pressure. The higher air pressure in the inlet manifold is caused by the turbocharger.
The new 6V3150 Engine Pressure Group is a replacement for the former 4S6553 Engine Evaluation Instrument group which is canceled. The former 4S6553 Engine Evaluation Instrument group gives indications in relation to "absolute" pressure. When the former group was used, the atmospheric pressure had to be subtracted from the gauge indication to get the manifold pressure.
Illustration 1. The 6V3150 Engine Pressure Group.
Illustration 2. Face of the 6V4017 Pressure Gauge.The 6V3150 Engine Pressure Group gives a direct indication of the air pressure in the inlet manifold. This is possible because the two 6V4017 Pressure Gauges (-100 to 400 kPa, -15 to 60 psi) give indications in relation to the atmospheric pressure. This is the same type of indication (except for metric conversion) that is given in the Rack Setting Charts.