Vacuum issues

[kaos4379]

Reaching out to see if anybody has any info on this subject!! I have boosted my 350 with both the while and a ProCharger at separate times of course. My boost gauge stays around-10 to -15 normal driving and will only go positive wot after 4000k I have smoke tested and pressure tested I have the oil catch cans removed. ProCharger said I should be running at 0 during normal operation and then I would see the boost I paid for??
so question is what is normal driving vacuum supposed to be and when would it get to 0 normally.

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[honeybadger]

I'm assuming you're using a boost gauge that measures manifold absolute pressure relative to atmosphere? your numbers would make sense then sine you'd only reach 0/go positive once you have enough boost to overcome atmospheric pressure

 

[robvas]

Throttle determines if you are going to make boost or not (part throttle will not)

RPM determines how much boost you will make (max boost at max RPM)

Your video looks normal. Probably won't make positive boost until 3/4 of the pedal is down. You will very, very rarely be at '0' on a gauge that shows both boost and vacuum (you'd be at 0 most of the time on a gauge that only shows boost)

While your engine is making vacuum during part-throttle (or no throttle), the bypass valve will be open and vent all the boost the supercharger is making to the atmosphere (that's the shhhhhhh sound you hear at idle)

 

[SheepDog]

You aren't going to see boost, when the throttle is nearly closed. All of the pressure from the blower is going out of the BOV. Put the skinny pedal on the floor and try again

 

[SnowFox]

Reaching out to see if anybody has any info on this subject!! I have boosted my 350 with both the while and a ProCharger at separate times of course. My boost gauge stays around-10 to -15 normal driving and will only go positive wot after 4000k I have smoke tested and pressure tested I have the oil catch cans removed. ProCharger said I should be running at 0 during normal operation and then I would see the boost I paid for??
so question is what is normal driving vacuum supposed to be and when would it get to 0 normally.

Sounds about right for a centrifugal blower. (You mentioned you went from a Whipple to a procharger yes?) so I'm sure you aware they will deliver boost somewhat differently.

Under normal driving conditions I don't see boost till about 3k RPMS give or take. And that's totally normal.

What BOV do you have? What is the Spring inside rated at?

 

[robvas]

Sounds about right for a centrifugal blower. (You mentioned you went from a Whipple to a procharger yes?) so I'm sure you aware they will deliver boost somewhat differently.

Whipple won't give you boost at light throttle either. You have to push the pedal down just as far as a centrifugal.

It will just give you almost full boost at low RPM instead of 1-2lbs when you do floor it.

 

[kaos4379]

I'm assuming you're using a boost gauge that measures manifold absolute pressure relative to atmosphere? your numbers would make sense then sine you'd only reach 0/go positive once you have enough boost to overcome atmospheric pressure

I have no idea what you are saying here.! Are you saying that the -15 is 0 in reality and I will gain from there? On my gauge that is.

 

[honeybadger]

I have no idea what you are saying here.! Are you saying that the -15 is 0 in reality and I will gain from there? On my gauge that is.

so there are two types of pressure sensors - those read relative to atmosphere (gauge sensor) and those that measure from 0/vacuum (called absolute sensors).Because boost gauges measure absolute manifold pressure, you'll only see a positive pressure when the blower is providing more booth than vacuum being generated by the engine.

 

[Pistol_91]

I have no idea what you are saying here.! Are you saying that the -15 is 0 in reality and I will gain from there? On my gauge that is.

Your gauge is a vacuum and boost combination gauge. It's not just boost.
So it's reading vacuum AND boost. It'll never rest at 0 as long as it reads vacuum.

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