Boost Question

[spuds]

Hi,A noob boost question, but I can't seem to find the answer.

1) Why does a boost gauge show vacuum when the turbo isn't spinning?

2) Where exactly is the sensor mounted? (that might make me understant question 1)

3) What exactly is a vacuum line? Is it just the tubing that connects from the turbo to the engine or something?

Thanks in advance!

[goalguy02]

Your engine uses vacuum suction to run several things. Your PVC or crankcase ventilation system runs on vacuum, as well as your brake booster and a/c blend doors, fuel pressure regulator, etc. I like having the vacuum reading on a boost gauge so you know you have no vacuum leaks.

There is no sensor for a boost gauge unless you are using an electronic gauge. Standard boost gauges are analog and use a vacuum line tied into the stock vacuum lines to read vac. and boost. Under idle and low throttle driving, the motor is in vacuum, which helps run your accessories as well as vent fumes from the crankcase. Once the turbo starts to spool, the vacuum decreases. Once the vacuum reaches 0 psi and starts moving into the positives, it is boost.

Vacuum lines just run from different components under the hood. They are usually small black lines made of hard rubber. It is a good idea to replace them if they are old or brittle so you do not get vacuum leaks, which is when the vacuum system cannot hold a constant vacuum.

Think of vacuum this way.

Vacuum -------> Boost-10 -5 0 +5 +10

Hope it helps.