boost pipe size and pressure problem

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pulsarmad20

Member
Hi all

In abit of a pickle i have an aftermarket gauge in the car that i have just replaced as it didnt light up.

The problem is the old one was reading 1 bar and this one is reading 0.6/0.7 standard boost?

and the standard boost gauge reads 10 out of 14 psi which also means 0.7 bar.

why ?

what is the standard pipe size for actuator to boost regulater/ dawes device to plenum then to standard boost gauge sensor and for an after market boost gauge would it be the same size pipe to what ever the standard is?



thanks

sam
 
PobodY

PobodY

Moderators
Staff member
red reading said:
because your car is making 10psi boost at a guess..............lol
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That's what I'd say too; if both the after-market and standard gauges are reading (about) the same value, they validate each other which suggests it's a pretty accurate figure.

If the old one didn't light-up and required replacing, could it also have not been reading correctly? Did it read 0 with the engine off and -0.something at idle?

I think all those lines are something like 8mm hoses.
 
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pulsarmad20

Member
ok thanks i have just had a look and it appears that the old gauge has a very small hole and the newer one has a bigger hole could this make them read different between the 2?


thanks
 
Fusion Ed

Fusion Ed

Active Member
No, as the pressure changes but there is no airflow to speak of so they equalise very rapidly. Hole size wont matter in this case.
 
M

Makaveli_se7en

Member
Diameter won't make a difference to the reading but can have a small effect on the response. The main factor in getting accurate readings from pressure tappings is how the enters the flow i.e. pertruding into the flow will give a slighlty different reading to one that is level, which n turn would be different to one with a chamfered edge.

As a side have you ever noticed how the pressure ratio on compressor maps is total to total pressure, whereas your boost tapping is reading static pressure and as the flow is moving through the pipes at a reasonable velocity there is quite a high dynamic component. Just food for thought
 
PobodY

PobodY

Moderators
Staff member
Makaveli_se7en said:
As a side have you ever noticed how the pressure ratio on compressor maps is total to total pressure, whereas your boost tapping is reading static pressure
Click to expand...
Yes! - I've actually had this argument with someone; essentially that the manifold pressure is +1.0 bar (as an example), so if the ambient pressure is already at 1.0 bar that makes it 2.0bar total pressure in the manifold.

Same thing with the coolant system; a 0.9bar car doesn't open at 0.9bar or it would only close when you're up a mountain. It's 0.9 over atmospheric, so opens at a total pressure of 1.9bar (if using 1.0bar as atmospheric pressure again).

The compressor map does make it a little confusing, but I usually subtract 1 from the pressure value and read that as the "boost" figure.
 
M

Makaveli_se7en

Member
PobodY said:
Yes! - I've actually had this argument with someone; essentially that the manifold pressure is +1.0 bar (as an example), so if the ambient pressure is already at 1.0 bar that makes it 2.0bar total pressure in the manifold.

Same thing with the coolant system; a 0.9bar car doesn't open at 0.9bar or it would only close when you're up a mountain. It's 0.9 over atmospheric, so opens at a total pressure of 1.9bar (if using 1.0bar as atmospheric pressure again).

The compressor map does make it a little confusing, but I usually subtract 1 from the pressure value and read that as the "boost" figure.
Click to expand...
Thats slightly different, thats about the difference between gauge and absolute pressure. Remember the Y-axis on a comp map is a pressure ratio, not pressure.

I'm talking about the difference between total and static pressures.
 
PobodY

PobodY

Moderators
Staff member
Er...oh... maybe I don't get it after all; you're talking about pressure in terms of fluid dynamics, and I'm thinking about the pressure of a system? - This sounds like a classic case of the difference in persepective between an engineer and a chemist.

I always struggled to make sense of the compressor map, so it's not surprising to discover that I'm not reading what I thought I was.

Although it's not the same point, is my observation about relative (gauge) and absolute pressure still valid?
 
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