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Not sure if i done this right can someone give a little info.

I want to log vaccum with my 7531 box. I pluged a map sensor into the box(off a 95 chevy truck) and then ran hose from map sensor to the valve cover. Everything is sealed up.

When setting it up what all needs to be changed in box and what should it read? I done some seaching and got some good info just need a little more.

Any help? Thanks
 

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Thats a Single bar sensor right? FAST makes a nice one also.
Yes..... You have it right so far..It was a while back when I used it. Speak with MSD on the set up but most important remember when the graph is going DOWN you are make vaccum. You will be watching the PSIA gauge if I recall correctly. It is the opposite of the Racepak Log.
 

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Discussion Starter #3
Thats a Single bar sensor right? FAST makes a nice one also.
Yes..... You have it right so far..It was a while back when I used it. Speak with MSD on the set up but most important remember when the graph is going DOWN you are make vaccum. You will be watching the PSIA gauge if I recall correctly. It is the opposite of the Racepak Log.
Yes i think its single bar. I just want to make sure i am using it right. Thanks
 

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i bought ray's fast sensor..plugged straight to msd and ran a hose to the valvecover..very easy to do..and it shows on the data trace.
 

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Thats a Single bar sensor right? FAST makes a nice one also.
Yes..... You have it right so far..It was a while back when I used it. Speak with MSD on the set up but most important remember when the graph is going DOWN you are make vaccum. You will be watching the PSIA gauge if I recall correctly. It is the opposite of the Racepak Log.
How much should it pull down to with this type sensor?
 

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How much should it pull down to with this type sensor?
The "sensor" has nothing to do with how much vac it will pull down to. Its just the sensor. Your vac pump will indicate how much vac you pull. Also keep in mind how sealed up your engine is will play a vital role. We leave the line around 14" and finish around 19.5" on 1 gun. Wet sump system with Star machine vac pump. More important is that your tune does not loose vac. If you hurt a piston or rattle the rings your vac will indicate it. Lots of good threads on vac on YB. "search"
 

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the MSD will show "negative" pressure, whereas a vacuum gauge read in in/hg (inches or mercury) . one PSI = about 2 in/hg. Just like atmospheric pressure is 14.5 or 14.7psi (or 29.92 BAR) the 29.92 is read in IN/HG.so if MSD shows like -6psi that would = 12" vacuum.
 

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Ray is right. "Sealing" everything up will help, BUT, you also need to have the right vac pump & especially the right mandrel to turn fast enough to make the inches of vacuum you are looking for. We like to see about 14" when we cross, and an upward sloping graph, indicating on our racepak & moroso vac pump an engine that is very well sealed up with no ring problem. If I remember right, with the map sensor, the graph will be the opposite if all is sealed up right...sloping down vs. up.
 
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