Got the boost gauge installed today! Yay! Centri Supercharged Stang come inside.
 

So I installed my boost/vac gauge today since the weather broke a little. And let me tell you it was scary testing it out on wet roads. My car gets sideways way to easy. So here is my low down on the gauge maybe someone can fill me in. Sitting still and revving doesnt build boost... is that because there isnt a load on the motor (gauge moves to zero-maybe 1lb hard to tell because it revs so quickly)? Also boost is only shown at wide open throttle why is that? Sorry for the weird questions but I am one who likes to understand how things work. Thanks in advance. Btw I am running 9lbs of boost at 6k rpm on a 8lb pulley through a 3 row intercooler is that normal?

You're not building boost at idle because your bypass valve is open. Superchargers don't work on engine load like turbos do... it's simply a ratio between pulleys.

And we would need to know what size your pulley is to know if your boost readings are typical.

He says he's running an 8lb pulley

What the balls is an 8lb pulley? I want to know the diameter of the pulley, not the amount of boost "it should make".

I'm running a 3.33" pulley on my vortech and I'm making 6lbs... does that mean a 3.33" pulley is a 6lb pulley.... no that just means that's what I'm making with this size pulley? There are waaaaaay to many variables to say x pulley makes x psi.

Ok well the pulley on my procharger p1sc is the pulley that came in the kit to make 8lbs. I dont know the size in inchs. Also I didnt say at idle I would build boost I am not retarded. I said that it doesnt build boost when I am sitting still revving my car up (maybe a 1lb). And that it will only read boost at wide open throttle. I didnt know that the bypass was variable dependant on the throttle position. I.E. Cruising down the highway at 3k rpm at part throttle I am still in vac. Smash the gas to the floor and we have boost.

EDIT: After searching around online I think its a good guess to say the "8lb" pulley is 3.9

I can bring my car up to redline without building any boost. It's all in how the bypass valve works. It needs a certain amount of vacuum to stay open.

See thats just it and what is confusing to me... Guess I am going to do some research.

He's talking about the stock pulley that ProCharger advertises as an 8 lb pulley. He's getting 9 lb at 6,000 rpm. I'm getting 8.9 lbs at 6,000 rpm so if his mods aren't too different than mine he's running a 3.7" pulley.

A centrifical supercharger builds boost in direct proportion to engine rpm. Mine is 1.8 lbs at 2500 rpm and 8.9 lbs at 6,000 rpm. It always generates that pressure regardless of throttle position. If the throttle is closed that pressure has no where to go. Supercharger systems have a by-pass valve that releases the excess pressure either back to the intake or to atmosphere.

The vacuum/boost gage is measuring the vacuum or boost inside the lower intake. On naturally aspirated motors the only way that air gets into the motor is because the pistons pull it in as they go down. This creates vacuum. At idle our motors struggle to breath because the throttle is closed. This causes about 18 inches of Mercury of vacuum. Since it is easier for the pistons to get the air they need when the throttle opens up, vacuum drops off to near zero at wide open throttle.

Even though the supercharger is generating 1.8 lbs of boost at 2500 rpms, the vacuum/boost gage will still show a vacuum if the throttle is partially closed because the throttle is still restricting air to the motor. If you go wide open throttle at 2500 rpm then the boost is allowed to get into the motor and the vacuum/boost gage will register around 2 lbs of boost. As rpms increase the boost gage will continue to go up until it reaches 9 lbs at 6000 rpms. If you let off the throttle at any time the gage will drop back to vacuum because you've cut off the air to the motor. The 9 lbs of boost is still being generated but its flowing out the by-pass valve instead of going into the motor.

I guess I'm confused about what you're confused about...

I knew what he was talking about, I was just being difficult to try and prove a point.... I know I know. I want people to understand that the same blower and the same pulley is going to make different psi numbers based on the engine setup. And you can't simple call a pulley a x psi pulley.