Teach me about vacuum

So, the boost gauge is in and I get 20hg on the vacuum side and 15-17psi on the boost side (under load).

Please explian vacuum to me. I guess I need a complete explaination because I know nothing about it at all.

Gas engines produce vacuum by themselves. The advantage of using this vacuum is that the power of the vacuum can be multiplied many times to produce a very strong pull. Good example of this is the master cylinder on a car with disc brakes.

you get vacuum in you intake manifold because the throttle plate is closed blockin air flow and because the engine when running "sucks" air. so when you have something sucking in basicaly a closed chamber (intake manifold) it creates vacuum...
vacuum basically = air at less than ambient pressure

Thanks guys.

Can I assume that the greater the vacuum, the better the engine is running ??

20hg on your gauge is 20" mercury. One atmosphere is a little less than 30" mercury or 14.7 pounds/square in.
By lightly using the gas peddle and keeping vacuum high, you will improve your gas mileage.

Dude 1 atm is 14.7 i dont understand how atmospheric pressure could be both pressure and vacuum

Average sea level air pressure is 14.7 pounds/ square inch which is one atmosphere. The boost-vacuum gauge reads zero for this pressure.
Vader's gauge reads vacuum in inches of mercury and boost in psi.

yes atm is 14.7psi vacuum is mesured in hg

yes so basically were under pressure all the time

Yes, we couldn't live, and our cars wouldn't run without oxygen.

A column of air one inch square, reaching into space from sea level, would weigh 14.7 pounds.
A column of hg (mercury) one inch square, 29.92 inches high would also weigh 14.7 pounds.

http:ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/prs/def.rxml