vac pressure?

[supranerd1987]

I did a search but did not find anything.... I just recently installed a boost gauge, it holds 10-11 psi strong under full throttle but idle it sets at about 20 vac pressure. Is this normal or is there a leak somewhere?

thanks

[TcmaBoy]

That is how it is supposed to be. A turbo does not make boost off idle like a roots blower does. It needs to spin up to a point where it is pumping more air than the engine is taking in. This is usualy arround 2500 RPM. The point where positive pressure begins is called the boost threshold. Until the engine reaches this point it operates like any other NA engine. This is why you feel a sudden surge in power when the turbo starts generating boost.

[Jeeves]

Vacuum differs from car to car depending on options and such.

[bgrieger]

A stable 20 inches is pretty good vacuum.

[supranerd1987]

cool thanks alot