My boost gauge reads about -12 to -13 inGh at idle, and when it coasts on highway, about -18 inGh. Is this normal? or could it mean a leak?

 

You will be in vacuum at idle and cruising. What is done to your car?

 

yeah. Apexi computer, 3 in downpipe, new motor and new turbos, 3 in exhaust, and thats it really. No big mods.

 

What port on the motor and what's your car idle at?

It boosts fine tho?

 

Not sure about the port. Isles at 12-13, drives down the highway at about 16-18. Boosts to about 9 lbs

 

if it boost to 9 lbs then no there is not a boost problem

 

yep, vacuum will increase when coasting. Normal.

think about it, the engine has a stronger sucking action (vacuum) when the RPM is increased but your not on the gas (so no boost), because the engine is sucking in more air, due to increased rpm's etc.

 

I think these guys are saying the larger the ports in your engine the less vacuum it will pull. They're asking if your motor is streetported.
A stock motor pulls more than yours. I'm getting 17 in each of my FDs. Stock boost is 10psi.
We don't know if you have a boost leak or not. You could be set to 15psi and only getting 9 because of a leak. Check out tons of sticky threads and read other threads in here as you see them to pick up knowledge. There is a lot to learn and knowing bits and pieces doesn't do the trick on these cars, you really have to have a good understanding if you are going to tinker with it. I really suggest to you since you are new that you leave the boost alone....I know you are installing a boost gauge, just don't alter the boost or mod the car on your own or you'll need another set of turbos and another motor.