Boost Reading

[NARTRI]

hi

previously when i tested my friends boost gauge i tap it where the actuator is and reads 10 - 11psi this was 1 month ago

now when i installed mine (yesterday) in and tap it from the intake manifold (where the stock gauge gets its reading) i get 7psi at full boost

car is using r32 actuator so i know it should be getting 10psi

so is my actuator stuffed or is something else or it meant to belike that?

Edited June 7, 2009 by NARTRI

[Moodles2]

What car is it? with R32 GTRs at least the stock gauge gets it's reading from balance tube which in turn is connected to the pressure regulator

[NARTRI]

car is r33 gtst

[HEKT1K]

when you are hitting 7psi.. what is the stock gauge reading?

if the stock gauge is the same then it's more likely your actuator isn't working properly, but if the stock gauge is hitting about 10psi or thereabouts it may just be the new gauge install.

does the car run any differently? without looking at the gauges does it feel like it used to?

[NARTRI]

with stock gauge it reads just above half way up from 0 and +7 at full boost cant remembe exactly

with driving dont notice any different

[gotRICE?]

So your saying you have a VAC hose going from the Actuator to the stock boost gauge tap on the IM?

I think thats way to long. Plumb the actuator up to where the stock actuator plumbs in and it will work. Dont forget to remove the boost solenoid too.

Take the solenoid out, plug the nipple on the intake, and run one line to the actuator. Whallah. 10psi

[NARTRI]

the solenoid have being taken out and plugged the nipple on the intake when i installed the actuator in

no no no everything is where it meant to be i didnt reroute the hose at all

the first test the aftermarket boost gauge line was tapped to the actuator and the second test was tapped to the IM

guess im gonna tap it again to the actuator and see how that goes see which is faulty

[**RB2530**]

You will get a pressure drop throughout your intake system. ie pressure in plenum will be lower than at the outlet of compressor. How big the drop is depends on a quite a few things...btw a drop from 10 to 7psi is pretty poor....

The implication of this is that with a fixed WG actuator, the boost pressure at the plenum will change depending on where the feedback for the actuator is taken..ie whether it is taken from the plenum, intake pipework or directly after the compressor...

[**RB2530**]

Also the stock boost gauge is not very accurate and is scaled in mmHG... Cheap aftermarket gauges too are worth every dollar you pay for them...ie not very accurate either...

[NARTRI]

thanks for the input **RB2530**

yeah i know the stock gauge aint that great and in mmHG

thats why i stay away from cheap gauges no point spending money over something aint worth using

[gotRICE?]

Sorry i didnt read the post properly, didnt realize you were talking about gauges!

I plumbed my Apexi gauge into the Vac line to the FPR, so essentially the same place (manifold), and it reads 10psi perfect.

Maybe there is a problem with the gauge? Tried testing it with someone elses?

Reason i say this is because its a bit easier than changing actuators

That, or someone sold you an R33 actuator. They are 7psi. Could be possible..

[NARTRI]

thats cool gotRICE

i wont be able to do some testing till the weekend which kinda ticks me off a bit but oh well

na i know the actuator is off a r32 been using it for about a year now and had borrow a mates gauge to made sure

ill let everyone knows after the week is over dam i soo hate exams

Edited June 8, 2009 by NARTRI

[SLAPS]

If its a r32 rb20 actuator it will definitely be running 9-10psi.

Back when I ran the rb20, stock turbo and stock exhaust with compliance cat it was running 9psi. Full 3" boost rose to 11-12psi.

Hows the cat?

All though unlikely IMO checked for boost leaks?

Edited June 8, 2009 by SLAPS

[**RB2530**]

Just for interest sake, the following is a good way of testing the accuracy of a boost gauges is as follows.

Go to the chemist and ask for a 15 or 20mL syringe. Even larger ones are fine. The bigger the syringe the harder you have to push the plunger. The syringe is plumbed up to the boost gauge and when you press the plunger the boost gauge will register what pressure is in the syringe.

To check the calibration there are three ways:

1. If you have a gauge that you know is accurate, plumb this gauge up with the other gauge and then to the syringe all at the same time. They will see exactly the same pressure as each other so you can compare the two readings.

2. If you don't have another good gauge, you can calculate the pressure exerted by the syringe by doing the following. Measure very accurately the diameter of the bore od the syringe. Calculate the area. Measure the very accurately the force exterted on the plunger. This can be done by placing the syringe in vice and placing a weight of known mass on the syringe. Put some light oil (vegetable oil etc) in the syringe. Don't fill the syringe. The oil is just to reduce the friction of the plunger in the bore.

The pressure out of the syringe will be the 'force on the plunger' divided by the 'area of the plunger'. It is reasonably accurate. The main source of error is in the physical measurement of the area and force plus the friction of the rubber plunger on the bore. You will need to know a bit about physics to get the units right. If anyone is interested in doing this I can work it out for you...

3. Use a proper gauge calibration tool. Don't know how much these cost but they basically use the same principle as option 2 but are a lot more precise.

These methods beat trying to do road tests and are better for your licence.

[NARTRI]

thanks guys for your help

it turns out the actuator is playing up

i put back the stock actuator and seleniod and works fine boost reads proper