Help With Info on PSI's

[cranshinibon]

Ive been looking at peoples pics of the interiors of their cars and im not really sure what the psi gauges are supposed to be used for. i know it has something to do with the turbos but what does psi really tell you?

[OMGz Turbo]

Actually there are various ones. I have seen some used for oil pressure and such. So depends on the gauge i guess

[Vypurr]

PSI is only a measurement of pressure. That is the Standard Measurement, and BAR is the metric measurement.

PSI is used for Fuel pressure, oil pressure, manifold pressure (boost), and a slew of other things.

For boost gauges which you are talking about PSI measures the pressure inside of the manifold, or a measurement of how hard the turbo is pushing air basically. You will notice that there is vaccume and pressure on the gauge to show if the manifold is pressurized or not.

[TROLL]

psi is pounds per square inch... its a measurement of pressure. in turbo cars you'll see boost gauges, but yeah i guess also fuel pressure, oil pressure, etc.

[cranshinibon]

thanks for the info but i guess i didnt ask exactly what i wanted to know.

what does it help benefit when you see the pounds per square inch when you have a turbo...if you have higher psi does that mean more power going to the turbo before the shift?

[Vypurr]

You need to know what is going on and how much PSI you are running to make sure its not broken!

If I see my PSI go up to 25, I know there is a big problem and if I keep my foot into the pedal, my car will blow up. But if its sitting at 17-18, I know that its in the correct range.

[IBTrends Tom]

easy explaination is this..
For all N/A motors there is no pressure build up inside the intake manifold, its always in vacuum b/c the motor is always trying to suck in air..

For Turbo cars you get the opposite there is pressure acually building up inside the manifold b/c air is being forced into the manifold(IE why turbocharging is called forced induction) for the air not being able to get sucked into the motor it is staying inside the manifold THUS creating boost pressure. hope that helps

[Nors]

easy explaination is this..
For all N/A motors there is no pressure build up inside the intake manifold, its always in vacuum b/c the motor is always trying to suck in air..

For Turbo cars you get the opposite there is pressure acually building up inside the manifold b/c air is being forced into the manifold(IE why turbocharging is called forced induction) for the air not being able to get sucked into the motor it is staying inside the manifold THUS creating boost pressure. hope that helps

There is no added pressure (boost), but there is still atmospheric pressure. Vacuum is only created in close/partial throttle situations not at WOT (wide open throttle).

[IBTrends Tom]

no added pressure when?? u do know a boost gauge compensates for atmosperic pressure(14.7) right??

i have no idea wat ur trying to say at all.. stick ur hand over ur intake and hammer the gas.. wat happens????? on WOT the closest u'll get to boost is 0 lol.. which is pretty obvious...

[Nors]

no added pressure when?? u do know a boost gauge compensates for atmosperic pressure(14.7) right??

i have no idea wat ur trying to say at all.. stick ur hand over ur intake and hammer the gas.. wat happens????? on WOT the closest u'll get to boost is 0 lol.. which is pretty obvious...

I am saying the engine isn't always creating a vacuum. I'm not saying a boost gauge will read 14lbs on an NA engine. I am saying boost is added pressure.

I think you are confusing my post a bit.

At WOT there is actually a little vacuum but for the most part its considered 0. Edit: I forgot this thread was about boost gauge and got a little ahead of myself.

[IBTrends Tom]

ur making something so simple seem so technical...

I'm not accounting AP as a type of ADDED pressure its always there so i neglect it as most do..

and who doesnt know that boost is pressure?? that is something a scrub even knows

and as for ur WOT comment ur just reiterating something i already said..

[turbo4g63]

i am gonna try to stay away from this thread b/c i am not much of a teacher. just for monitoring pressure, for ex, boost, fuel, oil pressures. I use my boost gauge for monitoring. i don't really look at it all that much unless i adjust my boost controller.

i can tell by the original post that you don't know much about turbo's and such, but that is exactly what these forums are for.

[Wiisass]

and BAR is the metric measurement.


pascals (pa) is the metric measurement of pressure. You will more commonly see kilopascals (kpa) because a pascal is pretty small.

Just to clear up all the confusion from some of the posts above mine. Boost gauges do not account for atmospheric pressure. They're gauges, they read gauge pressure. The absolute pressure in your intake manifold will be whatever your boost gauge reads plus atmospheric pressure. That's why if you had a boost gauge on an NA car, it would read zero because pressure in the intake manifold is equal to atmospheric pressure.

[cranshinibon]

thanks so much guys i really appreciate the help..im kind of happy that there was somewhat of a debate going on so i could see more in depth as to what they are for. im still a noob to turbos but i have a general idea of how they work and why you'd need a psi gauge. you guys are awesome

[Wiisass]

stop calling it a psi gauge. It's a pressure gauge and depending on what pressure you are measuring, it should be noted as such. For example, oil pressure gauge, boost pressure gauge, water pressure gauge, etc. It's like calling a water temp gauge, a fahrenheit gauge or a celsius gauge or a kelvin gauge. They're units, they aren't a description of what the gauge measures.

[Renegade_]

All that those guages measure is how much pressure is inside the lines, engine manifold, etc etc.

A boost guage you run off of the piping post turbo so you can see how much air pressure is built up inside of the manifold and piping. high PSI = more air being flowed, but then again that all depends on what turbo.

For example, a stock USDM STi turbo (VF39) at 1 bar will not flow twice the airflow of a JDM WRX RA turbo (VF22) at .5 bar. Since the VF22 is larger than the VF39 it takes less PSI to flow the same air. I don't have compressor diagrams to compare them but for sake of argument and to put it in perspective, a larger turbo might have to flow .7-.8 bar where another one would have to flow 1.0 to move the same air.

If you don't know this already, 1 bar = 14.7 psi