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What is the factory vacuum value?

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Healthy manifold vacuum value is about the same on almost every gasoline engine and varies a lot depending on level of internal friction in the engine like oil temperature/viscosity.


But it's a very crude value to use, and don't tell you much.


What you really shall look for is the compression of each cylinder at three cases:


  • Cold engine in "dry" situation.
  • Cold engine where you have injected some oil into the cylinders and cranked it around a bit with plugs out.
  • Hot engine.

If the cold engine differs with and without oil you may have a piston ring issue.


Difference between cold and hot indicates that the valves may need to be taken care of.

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Unfortunately, due to the horizontal layout, the only compression test that's really feasible is cold & dry.


OP, are you looking into a problem or just want to take general stock of your engine's health? If the latter, a priceless toolset is an OBDLink MX Bluetooth dongle and the BtSSM Android app.

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@relative4 Just checking the general health of the engine. The car has 104k miles and is well taken care of but since I am going to "bulletproof" the intercooler I might as well take vacuum reading and check for leaks if the reading is low
Incidentally, if you do have any vacuum leaks, tbe fuel trims will tell you much more about that than a vacuum gauge will.
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@relative4 Old habits from owning and working on 80s BMWs.


Been reading on the open source software and was wondering if they will read the tune map installed by Cobb APV3?



@JmP6889928 Thank you. Finally have your correct username for future VF52 option. Will be PM'ing you sometime soon

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also worth noting that elevation can significantly lower vacuum readings as well. when I first got my car i spent a lot of time trying to figure out why the vac readings were so much lower than reported on here. pretty extreme here at 7000 ft but worth noting. also good to fill out your profile with location and car info so we can see some of those other factors when you post.
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