boost gauge
{{Short description|Type of pressure gauge}}
A boost gauge{{cite book|last=Bell|first=Corky|title=Maximum Boost : designing, testing, and installing turbocharger systems
|year=1997 |publisher=Cambridge, MA : Robert Bentley Automotive Publishers |isbn=0-83760-160-6|url-access=registration|url=https://archive.org/details/maximumboostdesi0000bell/}} is a pressure gauge that indicates manifold air pressure or turbocharger or supercharger boost pressure{{cite book|last=Goodsell|first=Don|title=Dictionary of Automotive Engineering|year=1995 |publisher=Society of Automotive Engineers |isbn=1-56091-683-4|url-access=registration|url=https://archive.org/details/dictionaryofauto00good}} in an internal combustion engine. They are commonly mounted on the dashboard, on the driver's side pillar, or in a radio slot.{{cite web|last=Knowling |first=Michael |url=https://www.autospeed.com/cms/a_110810/article.html |title=Basic Hands-On - How to Fit a Boost Gauge
|publisher=www.autospeed.com |date=7 October 2008 |access-date=15 May 2024}}
Turbochargers and superchargers are both engine-driven air compressors (exhaust-driven or mechanically driven, respectively) and provide varying levels of boost according to engine rpm, load etc.{{cite web|last=Markus |first=Frank |url=https://www.motortrend.com/how-to/turbocharger-vs-supercharger-whats-difference-types-explained/ |title=Turbocharger vs. Supercharger: What's the Difference?
|publisher=www.motortrend.com |date=5 March 2024 |access-date=15 May 2024}} Quite often there is a power band within a given range of available boost pressure and it is an aid to performance driving to be aware of when that power band is being approached, in the same way a driver wants to be aware of engine rpm.{{cite web|last=Voronov |first=Dmitry |url=http://speed.academy/turbocharging-for-the-race-track-borg-warner-9280/ |title=Forcing the issue: Making big power around a road course
|publisher=BBA Media |date=2 April 2019 |access-date=15 May 2024}}
A boost gauge is used to ensure excessive pressure is not being generated when boost pressure is being modified to levels higher than OEM standard on a production turbocharged car. Simple methods can be employed to increase factory boost levels, such as bleeding air off the wastegate diaphragm to 'fool' it into staying closed longer, or installing a boost controller.{{cite web |url=https://www.turbosmart.com/news/how-does-a-boost-controller-work/ |title=How Does a Boost Controller Work?
|publisher=Turbosmart |date=27 October 2021 |access-date=15 May 2024}} To prevent the Air-fuel ratio from going lean (caused by increasing the boost beyond the fuel systems capacity) care must be taken to monitor boost pressure levels, along with oxygen levels in the exhaust gas, using an air-fuel ratio meter that monitors the oxygen sensor.{{cite web|last=Neophytou |first=Stavros |url=https://www.fastcar.co.uk/tuning/fast-car-air-fuel-ratio-guide/ |title=Air Fuel Ratio Guide: How To Keep Your Engine Safe
|publisher=Kelsey Media Ltd |date= 20 October 2023 |access-date=15 May 2024}}
A boost gauge will measure pressure in psi, bar or kPa; many also measure manifold vacuum pressure in inches of mercury (in. Hg) or mm of mercury (mm Hg).