What Does A Negative Boost Reading Mean?  

DreamensioN

You mean a vaccum reading?

It simply means you're not boosting -and the engine is sucking air (creating negative pressure) instead of being force fed (positive pressure).

SkiDMaN

what he said

engine sucks of air when ur idling cause its the only way it can breathe... but when u start putting ur foot down... it breathes then the turbo supplies it air which is force fed... i guess its like resusitation *sp*

a normal person breathes... sucks air
but when ur resusitating ur blowing air into them

ok... maybe that was a stupid example... but eh

NOS Junky

great example i thought

frankxinyu

but i mean when its vacumm, shouldnt it be reading 0 psi rather than negative?

racsov500

Id imagine that 0 psi is the point whether it is neither sucking or blowing, its balanced..hard to describe..

meh

cyo00

It's not a reading of negative boost, it has a vacumm reading aswell. That negative reading (vacumm) is measuring the amount of air that is getting sucked in to the engine, got nothing to do with boost.

DreamensioN

0 psi is equal to atmospheric pressure.

If we take the turbo out of the equation - what do we have? An NA (naturally aspirated) engine. These engines always create a vaccum in the intake - because they need to suck their air through the filter.

Lets add a turbo/supercharger to that - now we have an engine that can be force fed air.

From your airfilter to the compressor wheel of the turbo - that part of your engine is ALWAYS in vaccum (meaning it's always sucking - no matter what). From the turbo onwards, this can be in positive pressure, or negative pressure depending on the load on the engine, your RPM and various other factors.

Your boost gauge measures boost in the intake manifold (behind the throttle body).

When you're sitting idle - you are not creating any boost - so your engine is sucking the air through the intake system...thus creating negative pressure. When you accelerate and there is load on the engine, your turbo spools up and crams more air into the intake than what the engine is sucking - this is boost.

You can get 0 psi, but only when the air you're pushing into the intake, equals the air that is being consumed - which is atmospheric pressure. This is the same as if you turned your engine off and everything equalises.

Make sense?

NiSlo

That just means that the engine is sucking the same amount of air that the turbo is forcing in to it.

MEV09

hahaha i used to have the same thoughts about my 300 when i was driving it..... but that was my first turbo it is the whole learning curve. good to have people you can ask about things though

frankxinyu

yeah, it does. thanx very much!

killswitch_13

An easier way too explain the negative reading is when it is at the lowest negative reading it means your throttle is closed (or nearly closed)... as it rises and starts heading to zero means your throttle is opening and at the point of zero your throttle should be completely open, therefore creating the maximum vacuum, and that is the point where the turbo starts creating some boost, so therefore if the needle raises above zero, you are creating some boost!!!

racsov500

yeah there we go!