I have an LT1 with a Vortech S-Trim Supercharger. I have an Autometer Boost/Vacuum Mechanical Gauge. I have the vacuum line attached to the manifold on one of the stock vacuum ports. When my car cranks, it pulls vacuum but when I rev the motor. It increases the vacuum readout to near 20psi. Any Idea why my gauge isn't working right?

Thanks,
Brandon

 

Belt driven, So hmm. Is the belt on the supercharger? I would guess so, since that would be dumb not to have it hooked up and expecting boost. I would say that your supercharger may not be producing any boost. As overall the vacuum you are describing is normal with a N/A engine. Unless I am missing something.

 

You generally won't make boost by reving the engine using a centrifugal supercharger. Get it out on the road, load it up and see if your gauge is working correctly.

 

is the s trim on backwards?

 

exactly. you wont see boost in neutral. when you rev it up and let go of the throttle it builds vacuum even more than idling. you need to load the engine.

 

BATTLE OF THE BOOSTS!!

Soooo..... which is it. I'll tell you this, I called Vortech and asked them (couldn't do this last night, sorry). They said you wont see boost on a gauge, but at a neutral trottle the boost bypass valve opens due to vacuum in the manifold opening it. This happening allows the volume of air produced by the spinning supercharger to be the same as with a load. BUUUTTT, since the boost bypass valve is open, the pressure (i.e. boost) is never collected. The only thing that increases is the vacuum that holds the bypass open, hense the reading. Vortech said get it on the road drive it, then I will see boost. Haven't done it yet but hopefully i will soon.

Hope this clears things up...

 

im gonna guess that like I and the others have said, you will see boost on the road. I tried the same thing when I first put it together with the same results, and im sure the others who've told u the same did as well. Take a picture of your face the first time you feel the boost rip the tires off in 1st and pull through 2nd. I know I was like a little kid on christmas day with a tree full of presents just for me!

 

LOL, will do. I can't wait to catchem' on fire. lol