[JETmn]

Originally Posted by Dark_Knight_335

You mean it's not Plutonium Seconds per Inch?

Oh wait, this is a real thing!

https://en.m.wikipedia.org/wiki/Inch_of_mercury

Yes, and most cars I have had run 15-25 inches of vacuum so that would put your -19 right there.

[trixdout]

No vacuum shows on the boost gauge for an n55.

[Dark_Knight_335]

Originally Posted by trixdout

No vacuum shows on the boost gauge for an n55.

Yea that's what I figured. It's attached to the OBD port.

[stari335]

You guys are hilarious. Of course its normal to see vacuum on the boost gauge.

[Unklejoe]

Originally Posted by stari335

You guys are hilarious. Of course its normal to see vacuum on the boost gauge.

The N55 has Valvetronic. Valvetronic is a system that uses varying amounts of lift on the intake cam to "throttle" the engine.

The "vacuum" on an N55 exists only between the piston and the intake valve under normal conditions.

Normal engines use a throttle body to throttle the engine, so there will be vacuum everywhere behind the throttle body (facing the intake valve), but the N55 does not*.

*The N55 does include a throttle body, presumably for extra control by the ECU, but it's wide open most of the time.

However, even if the throttle body is closed, there should still be no vacuum since the pressure sensor is before the throttle body (in the intake pipe). Note that on most other cars, the MAP sensor is connected to the intake manifold (hence the name Manifold Absolute Pressure).

There may be a very slight vacuum caused by restrictions in the intake system due to large transients before the turbo has a chance to spool when you "stab" the throttle, but I'd expect it to be basically negligible.

[Tim603]

Originally Posted by stari335

You guys are hilarious. Of course its normal to see vacuum on the boost gauge.

Thank god a sign of reason. It all depends on how your boost gauge is setup. If it is OBD2 it will most likely not read vac as the MAP sensor reads positive presssure

If you have a boost tap, it WILL read vac which will be displayed as negative (I know this as my car has a boost tap w/ gauge and is completely normal)

Carry on

Edit: I am speaking in terms of N54 as I do not know enough about N55 to comment

[trixdout]

Originally Posted by Tim603

Thank god a sign of reason. It all depends on how your boost gauge is setup. If it is OBD2 it will most likely not read vac as the MAP sensor reads positive presssure

If you have a boost tap, it WILL read vac which will be displayed as negative (I know this as my car has a boost tap w/ gauge and is completely normal)

Carry on

Edit: I am speaking in terms of N54 as I do not know enough about N55 to comment

Yes the N54 has vacuum, but the N55 does not have vacuum in the cp. THe explanation stari335 gave is directly to the N55.