boost gauge pipe

[drifter17a]

All, 

 

I have searched various forums in hope of finding an answer. What I want to know is where should boost gauge pipe be connected to, before throttle body or after.

What I have seen and what seems to be majority view is before throttle body .

 

little background:

I have two boost gauges, one is evo ( see below) and one is the greddy boost controller

http://prosportgauges.com/evo-electrical-boost-gauge.aspx

 

there is a pipe after throttle boddy connected to a filter and then to a t which then goes to greddy and evo gauge.

 

Evo gauge is reading -21 or -22 psi on idle whilst greddy is -9.9

when it is building boost they seem to match with 0.2 to 0.5 psi difference . I am leaning toward beliving what is shown on greddy as it is a well known brand than evo which is after market .

 

so now for my questions, would you relocate the boost pipe to before throttle body ? i suppose before TP and after pressure when car is boosted should be the same, in another word the boost should no decrease when it is passing TP .

 

2. I seem to have a boost leak and have checked all pipes without an issue. What I suspect is, it is my blitz bov as it could be opening sooner than I could reach 10 psi( what I have set the greddy as). what is your view?

I am thinking of getting a new spring for the blitz bov

 

[r32-25t]

Boost gauge always goes in after the throttle body or won’t it read vacuum 

[Ben C34]

Also, it is not possible to read -21 psi at idle, so I would think the difference in readings is due to different units used.

Do a pressure test to check for boost leaks. Don't guess.

[GTSBoy]

1 hour ago, drifter17a said:

What I have seen and what seems to be majority view is before throttle body .

 

Not possible.  There are many dumb people in the world, but not enough for that silliness to become the majority position.

The only related thing that is true is that the boost source for running a boost controller must be before the TB.

[drifter17a]

9 minutes ago, GTSBoy said:

 

Not possible.  There are many dumb people in the world, but not enough for that silliness to become the majority position.

The only related thing that is true is that the boost source for running a boost controller must be before the TB.

I suppose you are refering to solonoid connection which connects to boost and your wastegate which is before tb

 

i only said what i had seen on forums and searches

 

re my negative psi, i have tripple checked every thing and all is in order. The fact that they match ( greddy and prosport) when boost runs through it says the prosport should work fine

 

i think -14.7 is ok, don’t ask me why but i recall a memory re 14.7 being the normal air pressure or something alike. Please excuse my ignorance but at -21 or -25 at times, it seems very odd

 

it could be greddy does not show a a bigger negative value as it is limited to -10 to 30-40 psi or whatever set by greddy

[Ben C34]

No, it is not at all possible to go below - 14.7 psi, the evo gauge is displaying inches per mercury for vacuum as negative psi isn't a proper way of measuring vacuum.

[Ben C34]

It's normal for a boost gauge to change units with boost and vacuum. Look at some mechanical gauges and you will see it written on them

[drifter17a]

8 minutes ago, Ben C34 said:

It's normal for a boost gauge to change units with boost and vacuum. Look at some mechanical gauges and you will see it written on them

So even though it is psi, it change to inch per m on negative?

[Ben C34]

25 minutes ago, drifter17a said:

So even though it is psi, it change to inch per m on negative?

Yep

[GTSBoy]

Yes, this is one place where the stupid are in charge.  Everybody in the automotive world uses inches of mercury or inches (or mm) of water to measure vacuum, regardless of how stupid it is to use the column height of a liquid to describe a pressure term.  Ask the Martians what pressure (in Pascals) corresponds to -300 mmH2O and they will give you a completely different answer to the people who live on Jupiter.

[drifter17a]

how would you know if BOV is leaking ?

 

mine is blitz and BOV off to air. I understand the suggestion of using the manufacture / the divertor but I do like the sound.

 

What I have read and understand from blitz is to turn the car on, adjust the screw and when it starts to idle rough or cylinder on BOV is open then tighten 1 turn . I have followed this but strongly belive my BOV is leaking .

 

I don't have air compressor at the moment to test so looking to get something and use my car tyre set to 20 psi and test for leak. in meantime I wanted to know, how can I know what spring I should use on BOV ? does it have to match with your desired boost ?

 

I understand the way BOV works is, it has two ports, one connected to after the Throttle body and one to the pipe before TB.

 

Pressure/Boost pushes the piston up and at the same time pressure from manifold/boost pushes it down from top so there is no way it could be opened during boost and when throttle is released the vacuum does create a suction from above and extra air pressure from when the TB is closed pushes the piston up so it is released. is this correct ? if so then what is the use of spring ?

 

I have noticed the BOV opened when I rev to 2-3 k which hardly creates 2-3 psi of boost even if I tight the adjustment all the way !

[drifter17a]

15 hours ago, Ben C34 said:

No, it is not at all possible to go below - 14.7 psi, the evo gauge is displaying inches per mercury for vacuum as negative psi isn't a proper way of measuring vacuum.

you are right, called prosport and was told what you said

 

you are a genuine and very confusing when you have a gauge that says negative pressure and shows PSI but it is inch Mercury and on positive it is PSI!

 

 

Have anyone used prosport, are they reliable at all ?

[GTSBoy]

I have multiple Prosport gauges in my car.  The white LEDs are all failing, half of the red LEDs are failing.  The green ones are OK.  It's just as well that I want them green.

The gauges have been working fine for years.  I do have one problem with the exhaust pyrometer.  It does weird things that I'm not going to bother to explain.  I would replace it with another of the same if I could be bothered doing anything at all about it.

[RBW49N]

 
Not possible.  There are many dumb people in the world, but not enough for that silliness to become the majority position.
The only related thing that is true is that the boost source for running a boost controller must be before the TB.

Why MUST it be before the throttle body?

[GTSBoy]

Imagine that you're operating the engine at part throttle.  Enough to make, say, 50% of your target boost (as measured inside the plenum, where you would expect to measure it).  There will be a sizable pressure drop across the throttle body - that's what the throttle is for.

Now, case 1.  Things set up the way that they are supposed to be.  Boost gauge in plenum, boost source for boost control actuation after the turbo but before the TB.  The boost controller will receive a larger boost signal because there is more pressure upstream the TB.  This effectively means that you will need to bleed more of it away in order to reach your target boost, but this is better than....

Case 2.  The boost controller's boost source is downstream the TB.  Now it is only seeing exactly the same boost value as the gauge.  And, as stated in the 1st paragraph, we're only seeing 50% of the boost target.  It is possible, under these conditions for the turbo to be working far too hard and overboosting in the pipe from turbo to TB because the wastegate should be shut because the boost signal to the controller is only ~50% of target.  In this situation, you end up needing much smaller throttle openings to make the same part throttle power, because of the high pressure in the inlet tract.  But, if you had an EFR or other speed sensitive turbo, it could spell insta-death.

If the throttle is wide open, it makes no difference.  But there is a lot of part throttle operation in most turbo cars, and no-one ever seems too think about that.