boost level on neutral gear?

[A80Avant]

Hello all,

i have been told lots of things about what the boost level should be when pressing the throttle on stationary car and keeping it at some rpm.A friend of mine tells me that on his car that uses a boost controler and a different wastegate by doing this he can keep 1.3-1.4bar pressure

On my car,as soon as i hit the throttle,my gauge shows from 0.5vaccum to 0.2 vaccum and then again drops to 0.5 vaccum either i keep a steady 4000rpm or i take it to the redline.

Can anyone tell me what is normal and what could this indicate?Is the wastegate opening and lets the air out?Am i having a boost leak?What should be happening when performing this test?

thanks
Vasilis

[Keith]

Hi,

You can not have any positive boost pressure on neutral.
Some systems exist to keep a positive pressure even when the car is not running . It's generaly used in car racing, called, if I remember well, Bang-Bang.
This name is used beacause of the exhaust explosions that this sytem induces.
You only can natrually have boost pressure when the car has resistant charge opposed to the engine.

You have some changes in your "vaccum pressure" (from -0.5 to -0.2) because when you throttle, little resistance from the engine mobile parts resistance and inertia, makes some little resistant charge opposed to the engine itself.

Consequence : pressure grows a little but not enough to get positive pressure.

If you had positive boost pressure on neutral it would mean that your engine begins to tighten or seize.

see you,

Keith

[newsh]

Absolutely, you don't get boost without the engine being under load.

[LHD_Kid]

There was that Umluft thing which Audi used, 2 wastegates and a special addition to the EM, as an antilag... supposedly produced something like 1.5 bar boost at tickover, as I understand it, but this was very hard on valves... there is a thread here about it somewhere, but this is obviously not very common on road cars.....

near the end of this threasd, some pics and an explanation...

Linky

[s2munckton]

i don't know all that much about this but i was always under the impression that you wont get boost in neutral unless you have a turbo back exhaust.

[Jamo]

No boost on the car unless engine under load

[kwlw]

i have been told lots of things about what the boost level should be when pressing the throttle on stationary car and keeping it at some rpm.A friend of mine tells me that on his car that uses a boost controler and a different wastegate by doing this he can keep 1.3-1.4bar pressure

0.4 bar on neutral maybe is with antilag...

On my car,as soon as i hit the throttle,my gauge shows from 0.5vaccum to 0.2 vaccum and then again drops to 0.5 vaccum either i keep a steady 4000rpm or i take it to the redline.

Seems pretty much normal.

Can anyone tell me what is normal and what could this indicate?Is the wastegate opening and lets the air out?Am i having a boost leak?What should be happening when performing this test?

It's normally indication of mixture richness and turbo speed. Which depends on every setup.

I can get around 0.2 bar positive boost on rev limiter. I'm running k26 turbo and custom intake on my AAN. This is not pressure gauge failure, because you can see as air hosses expand a little (they collapse a little under negative pressure). Pressure starts to build up from somewhere 6000rpm, followed with turbo spinup sound (I have very slilent exaust at the moment, and free intake, sound is exactly the same like on new diesels). Until that - it's nice -0.5 bar. This may be not positive indication, for example mixture is too rich, bad timing, MAF shows UFO location on Mars, not the air volume, bypass valve is not opening, wgfv valve stuck, etc, etc.

With failed maf and engine working something similar like anti-lag sometimes it fluctuated to 0.1-0.2 bar even on pretty low rpm (neutral gear).

So finalizing - there should be no possitive pressure in all rev range. However in some custom setups, which are done wrong or right - it can be some little pressure. 0.4 bar is overkill IMO. Maybe something is blocking intake ports in intake manifold...

Sau