AutoMeter 2-5/8" Sport Comp II Boost/Vacuum Gauge, 30 In HG/45 PSI, Mechanical (7608) Holley If you change the mass

If you change the mass of pistons

Made from 3 inch titanium and available with a burned blue tip or bare brushed titanium

this explanation is long and technical

with high-quality CNC machined billet components

When the valves are open

AutoMeter 2-5/8" Sport Comp II Boost/Vacuum Gauge, 30 In HG/45 PSI, Mechanical (7608) Holley If you change the massMechanical boost vacuum gauge with 2 5 8" dial, measuring 30 IN HG 45 PSI range, featuring white LED through the dial lighting and high precision bourdon tube movement. No electrical hookup required. Features: Modern white LED through the dial lighting provides clear visibility during nighttime use AutoMeter's race proven mechanical instruments provide trusted accuracy while being simple to install No electrical system required for gauge operation