Turbo gauge - how do I read it
#1
07-19-2016, 11:41 AM
Turbo gauge - how do I read it
Years ago when we bought our S60 it came with a Turbo gauge that was installed by the previous owner. They knocked the teeth out of the side vent to install it. 
The S60 was my first turbo and I am not sure about how to read the gauge. I know I am seeing vacuum but what do the numbers mean.
What should I see at idle?
At 3000 RPM the gauge is reading zero.
Not sure how accurate the gauge is because when the engine is off, the gauge doesn't sit exactly at zero.
Always wondered and it only took several years for me to ask.
Now back to my search for a used V50. I like our 07 V50 and we are thinking of getting another one.
The S60 was my first turbo and I am not sure about how to read the gauge. I know I am seeing vacuum but what do the numbers mean.
What should I see at idle?
At 3000 RPM the gauge is reading zero.
Not sure how accurate the gauge is because when the engine is off, the gauge doesn't sit exactly at zero.
Always wondered and it only took several years for me to ask.
Now back to my search for a used V50. I like our 07 V50 and we are thinking of getting another one.
#2
07-19-2016, 12:59 PM
Senior Member
The confusing part of the turbo gauge is vacuum and the dual scale.
Atmospheric pressure on earth, at sea level, measures about 30 inches on a mercury barometer. Traditionally, vacuum gauges for this sort of application are graduated from zero to 30, even though this is a system of measurements more suited to the middle ages. If you see that, zero to 30, 30 means outer space. zero is local weather. That is the short answer. if you see some other units let us know.
On a car that really runs efficiently at low speed, you could see vacuum in the 20's at idle. You may not see that on a turbo S60, but you tell us. You probably should see more than 15 vacuum at idle. That means the intake manifold pressure is at that level of vacuum, because the throttle is closed and the engine is running at that reduced pressure. That is because it's not generating any (much) power.
The pressure side is just like any pressure gauge. More is more. It should say on its face what units are used, but I an almost guarantee it won't be positive inches of mercury. For some reason they just don't do that. Under a load of course the pressure goes up, and with a turbo it'll go above zero, where cars that run on ambient air cannot. Mostly you just see that the turbo is working and the control system that controls boost pressure is working.
Atmospheric pressure on earth, at sea level, measures about 30 inches on a mercury barometer. Traditionally, vacuum gauges for this sort of application are graduated from zero to 30, even though this is a system of measurements more suited to the middle ages. If you see that, zero to 30, 30 means outer space. zero is local weather. That is the short answer. if you see some other units let us know.
On a car that really runs efficiently at low speed, you could see vacuum in the 20's at idle. You may not see that on a turbo S60, but you tell us. You probably should see more than 15 vacuum at idle. That means the intake manifold pressure is at that level of vacuum, because the throttle is closed and the engine is running at that reduced pressure. That is because it's not generating any (much) power.
The pressure side is just like any pressure gauge. More is more. It should say on its face what units are used, but I an almost guarantee it won't be positive inches of mercury. For some reason they just don't do that. Under a load of course the pressure goes up, and with a turbo it'll go above zero, where cars that run on ambient air cannot. Mostly you just see that the turbo is working and the control system that controls boost pressure is working.
Last edited by firebirdparts; 07-19-2016 at 01:02 PM.
#3
07-19-2016, 05:36 PM
Here are pics of my gauge. The one closest to zero is when the engine is off. The other one is at idle.
You can see that the gauge seems a bit out of calibration because at idle the needle isn't hitting directly on zero. Or is that the way it is supposed to look????
You can see that the gauge seems a bit out of calibration because at idle the needle isn't hitting directly on zero. Or is that the way it is supposed to look????
The confusing part of the turbo gauge is vacuum and the dual scale.
Atmospheric pressure on earth, at sea level, measures about 30 inches on a mercury barometer. Traditionally, vacuum gauges for this sort of application are graduated from zero to 30, even though this is a system of measurements more suited to the middle ages. If you see that, zero to 30, 30 means outer space. zero is local weather. That is the short answer. if you see some other units let us know.
On a car that really runs efficiently at low speed, you could see vacuum in the 20's at idle. You may not see that on a turbo S60, but you tell us. You probably should see more than 15 vacuum at idle. That means the intake manifold pressure is at that level of vacuum, because the throttle is closed and the engine is running at that reduced pressure. That is because it's not generating any (much) power.
The pressure side is just like any pressure gauge. More is more. It should say on its face what units are used, but I an almost guarantee it won't be positive inches of mercury. For some reason they just don't do that. Under a load of course the pressure goes up, and with a turbo it'll go above zero, where cars that run on ambient air cannot. Mostly you just see that the turbo is working and the control system that controls boost pressure is working.
Atmospheric pressure on earth, at sea level, measures about 30 inches on a mercury barometer. Traditionally, vacuum gauges for this sort of application are graduated from zero to 30, even though this is a system of measurements more suited to the middle ages. If you see that, zero to 30, 30 means outer space. zero is local weather. That is the short answer. if you see some other units let us know.
On a car that really runs efficiently at low speed, you could see vacuum in the 20's at idle. You may not see that on a turbo S60, but you tell us. You probably should see more than 15 vacuum at idle. That means the intake manifold pressure is at that level of vacuum, because the throttle is closed and the engine is running at that reduced pressure. That is because it's not generating any (much) power.
The pressure side is just like any pressure gauge. More is more. It should say on its face what units are used, but I an almost guarantee it won't be positive inches of mercury. For some reason they just don't do that. Under a load of course the pressure goes up, and with a turbo it'll go above zero, where cars that run on ambient air cannot. Mostly you just see that the turbo is working and the control system that controls boost pressure is working.
#4
07-19-2016, 09:43 PM
Senior Member
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