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Old 06-08-2005, 09:24 PM   #1
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Default Bought a 2000 ssei and have a boost question

I just bought a 2000 SSEI and when I am driving highway at 55 mph the boost is at -5.
Is this where it is to be?
When I put it to the floor board the boost is at +8. Can someone explain the boost thing to me so I know it is doing what it is supposed to be doing. If the super charger isn't doing what it is supposed to be doing will it throw a code? Thanks for your time
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Old 06-08-2005, 09:32 PM   #2
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your supercharger run just fine, dont worry.

if the gauge go from like -10 to +10 its because it should go there.

for the -5, im not qualified enought to answer you, but many member here know anything about that
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Old 06-08-2005, 09:33 PM   #3
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If your car had no supercharger at all, it would be reading -10 all the time. Typical manifold vacuum. Call it 10" of vacuum, but that'* not really what it is. The engine'* natural ability to suck air in, because the pistons are on the intake (downward) stroke, with the intake valve open.

Because you have a SC, you get POSITIVE pressure. -5 with light throttle or with the cruise set is typical. When you hit the throttle, it increases past 0 (atmospheric pressure) into the Positive displacement PSI range.
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Old 06-08-2005, 09:46 PM   #4
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Quote:
Originally Posted by willwren
If your car had no supercharger at all, it would be reading -10 all the time. Typical manifold vacuum. Call it 10" of vacuum, but that'* not really what it is. The engine'* natural ability to suck air in, because the pistons are on the intake (downward) stroke, with the intake valve open.

Because you have a SC, you get POSITIVE pressure. -5 with light throttle or with the cruise set is typical. When you hit the throttle, it increases past 0 (atmospheric pressure) into the Positive displacement PSI range.
Thanks that helps.
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Old 06-08-2005, 09:47 PM   #5
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Quote:
Originally Posted by sse for me
Quote:
Originally Posted by willwren
If your car had no supercharger at all, it would be reading -10 all the time. Typical manifold vacuum. Call it 10" of vacuum, but that'* not really what it is. The engine'* natural ability to suck air in, because the pistons are on the intake (downward) stroke, with the intake valve open.

Because you have a SC, you get POSITIVE pressure. -5 with light throttle or with the cruise set is typical. When you hit the throttle, it increases past 0 (atmospheric pressure) into the Positive displacement PSI range.
Thanks that helps.

like i said, they know their stuff!
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Old 06-08-2005, 09:59 PM   #6
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I would like to elaborate a little more. A positive displacement supercharger like our roots-type Eaton would always make boost, if it weren't for the wastegate. It is always moving a certain amount of air per revolution (well, it varies a little because the efficiency increases with speed). The wastegate is a butterfly valve that is opened or closed based on pressure on the inlet side of the supercharger after the throttle plate, it dumps most of the air back into the intake before the SC. As the throttle plate is opened, the pressure in front of the SC goes from -10 closer to 0 the more it is opened. As that happens, the negative relative pressure that was holding the wastegate open weakens, letting the wastegate close further and further, keeping more of the air in the engine and creating positive pressure, BOOST!
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Old 06-08-2005, 10:08 PM   #7
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well explain
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Old 06-08-2005, 10:16 PM   #8
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Quote:
Originally Posted by jwikoff99
I would like to elaborate a little more. A positive displacement supercharger like our roots-type Eaton would always make boost, if it weren't for the wastegate. It is always moving a certain amount of air per revolution (well, it varies a little because the efficiency increases with speed). The wastegate is a butterfly valve that is opened or closed based on pressure on the inlet side of the supercharger after the throttle plate, it dumps most of the air back into the intake before the SC. As the throttle plate is opened, the pressure in front of the SC goes from -10 closer to 0 the more it is opened. As that happens, the negative relative pressure that was holding the wastegate open weakens, letting the wastegate close further and further, keeping more of the air in the engine and creating positive pressure, BOOST!
Thanks this also helps
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