Vac / Boost Gage Reading ????
- Thread starter Granny 2
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Yes.. put it this way. If you didnt have any vac showing, you'd have a serious blowby problem.
The engine still has its own intake (vacume), and at highway cruise RPM, the turbo isnt spooling high anyway. Boost itself is actually the amount of pressure (in psi) MORE than what the engine is taking in on its own. Now when you get in the throttle, that turbo spools, then it rises above the "neutral point" i guess you could call it.. or atmospheric pressure which would be 0 on the gauge, and proceeds to build.
Here's an example. You're idling.. in gear.. dead stop. You mash the gas.. the gauge will go from reading vac to Zero.. then as the RPMs build, the turbo spools and starts shoving air into the intake and the gauge creeps up. The RPM gets to around 5,300 or more... it shifts into second. Notice as it shifts into 2nd gear, the boost jumps up a few pounds really quick. Why? Because all that boost is still there for the short moment that the gears change and the RPM drops. Meaning the engines not taking in as much for that very brief moment, therefore excess boost registers really sudden on the gauge.
Then when you're cruising and not putting any load or acceleration on the engine, its just sucking in air like a naturally aspirated engine... meaning vacuum. Thats why its better to have a gauge that reads boost AND vac. That way you can tell if you have a blowby problem for example. My motor is still pretty fresh and tight. It barely even burns any oil.
At least thats how mine runs.
The engine still has its own intake (vacume), and at highway cruise RPM, the turbo isnt spooling high anyway. Boost itself is actually the amount of pressure (in psi) MORE than what the engine is taking in on its own. Now when you get in the throttle, that turbo spools, then it rises above the "neutral point" i guess you could call it.. or atmospheric pressure which would be 0 on the gauge, and proceeds to build.
Here's an example. You're idling.. in gear.. dead stop. You mash the gas.. the gauge will go from reading vac to Zero.. then as the RPMs build, the turbo spools and starts shoving air into the intake and the gauge creeps up. The RPM gets to around 5,300 or more... it shifts into second. Notice as it shifts into 2nd gear, the boost jumps up a few pounds really quick. Why? Because all that boost is still there for the short moment that the gears change and the RPM drops. Meaning the engines not taking in as much for that very brief moment, therefore excess boost registers really sudden on the gauge.
Then when you're cruising and not putting any load or acceleration on the engine, its just sucking in air like a naturally aspirated engine... meaning vacuum. Thats why its better to have a gauge that reads boost AND vac. That way you can tell if you have a blowby problem for example. My motor is still pretty fresh and tight. It barely even burns any oil.
At least thats how mine runs.
I'd say -12 hg isn't bad at idle, but -15 hg is more like what it's supposed to be at. Mine gets -16 to -17 hg at idle.
At highway speeds, under light load, you should be somewhere around -10 hg. At -6 or -7 you are getting poor fuel economy as you are closer to the pressure side of things.
Stock or aftermarket cam?
At highway speeds, under light load, you should be somewhere around -10 hg. At -6 or -7 you are getting poor fuel economy as you are closer to the pressure side of things.
Stock or aftermarket cam?
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