Boost gauge reads below 0 when car is turned on.

[S_Ranger]

I've read somewhere it could be the boost gauge is reading from a negative source. But when I turn my car on it reads at the 20 mark below 0. I get on full boost and it reads correctly and all. Is this normal?

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[Zexell]

Yep, its corect. Its called vacuum.

 

[GST with PSI]

Yep that's normal.

see, essentially, all your "boost" gauge is, is a pressure gauge. anything that reads below zero is actually vacuum. you car at idle is not using the turbocharger, therefore just like any naturally aspirated car, your motor creates vacuum. however, when your rolling through town and mash on the gas, you wastegate opens and lets your turbocharger spool up. the compressor blades force air into the manifold which then raises manifold pressure to a positive level. this positive level of air pressure is refered to as boost. that's what i like so much about a boost gauge. it actually acts as 2 gauges in one. your boost gauge monitors you engine vacuum at idle and under low load conditions. it can tell you a lot about what your engine's doing internally.

 

[tstkl]

ok your wastegate opening is not what causes the turbocharger to spool, when your wastegate is open it reroutes exaust gas around the turbocharger so that the turbocharger doesnt spool anymore, its a way of controling boost pressure...

 

[RamenPride]

Yep, its corect. Its called vacuum.

yup, that's what the "VAC" means on that side of the gauge.....

 

[S_Ranger]

Thanks, rep points for everyone.

 

[GST with PSI]

ok your wastegate opening is not what causes the turbocharger to spool, when your wastegate is open it reroutes exaust gas around the turbocharger so that the turbocharger doesnt spool anymore, its a way of controling boost pressure...

Sorry. i ment wastegate closes. everyone makes mistakes, i was in a hurry.