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techtalk:ref:engmech04r [2020/10/20 22:56] hippysmack [Measuring Engine Vacuum] |
techtalk:ref:engmech04r [2020/10/21 03:34] (current) hippysmack [Measuring Engine Crankcase Vacuum] |
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And so, operating at higher elevations sometimes requires higher rated vacuum pumps to attain the same vacuum you would at lower elevations. \\ | And so, operating at higher elevations sometimes requires higher rated vacuum pumps to attain the same vacuum you would at lower elevations. \\ | ||
And likewise, operation at higher elevations affects the air/fuel mixture in the combustion chambers since air is less dense. \\ | And likewise, operation at higher elevations affects the air/fuel mixture in the combustion chambers since air is less dense. \\ | ||
- | + | ||
+ | However, it doesn't appear that elevation has much to do with the amount of vacuum created in the crankcase. \\ | ||
+ | A 12" pressure drop will still be a 12" pressure drop no matter if it drops from 50 or 5000 feet above sea level. \\ | ||
+ | The important number is the pressure swing. The more vacuum that is created, the farther away from atmosphere it becomes. \\ | ||
+ | The positive makeup pressure on downstroke normally brings vacuum back to near atmosphere. \\ | ||
+ | But an increase in vacuum lowers scavenging ability for the oil pump. \\ | ||
Gauge pressure is a measurement taken from the current atmospheric pressure level (depending on current elevation above sea level). \\ | Gauge pressure is a measurement taken from the current atmospheric pressure level (depending on current elevation above sea level). \\ | ||
When taking a vacuum measurement, you are measuring how much the air is lower than the current atmospheric pressure at your location (elevation wise). | When taking a vacuum measurement, you are measuring how much the air is lower than the current atmospheric pressure at your location (elevation wise). | ||
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* 1250cc | * 1250cc | ||
* The crankcase pressure had a mean vacuum of 21" of water column. | * The crankcase pressure had a mean vacuum of 21" of water column. | ||
- | * At 630 feet above sea level, ambient atmosphere is applying app. 29.24" Hg of force (397.52" WC or 14.36 PSIA). | + | * At 630 feet above sea level, ambient atmosphere is applying app. 29.24" Hg of force (397.52" WC or 14.36 PSIA). \\ (both outside in and inside out of a parked engine) |
* Vacuum at idle created by the pistons lowered ambient atmosphere inside by 21" WC. | * Vacuum at idle created by the pistons lowered ambient atmosphere inside by 21" WC. | ||
* So the mean pressure against the gaskets and seals at 1000 RPM (breather valves closed) was 376.21" WC (27.67" Hg or 13.59 PSIA). | * So the mean pressure against the gaskets and seals at 1000 RPM (breather valves closed) was 376.21" WC (27.67" Hg or 13.59 PSIA). | ||
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* [[techtalk:ref:engmech07p|Testing with a Slack Tube (Manometer) by bustert]], (elevation app 12.8 feet); | * [[techtalk:ref:engmech07p|Testing with a Slack Tube (Manometer) by bustert]], (elevation app 12.8 feet); | ||
* The crankcase pressure had a mean vacuum of 30" of water column. | * The crankcase pressure had a mean vacuum of 30" of water column. | ||
- | * At 12.8 feet above sea level, ambient atmosphere is applying app. 29.91" Hg of force (406.63" WC or 14.69 PSIA) | + | * At 12.8 feet above sea level, ambient atmosphere is applying app. 29.91" Hg of force (406.63" WC or 14.69 PSIA). \\ (both outside in and inside out of a parked engine) |
* Vacuum at idle created by the pistons lowered ambient atmosphere inside by 30" WC. | * Vacuum at idle created by the pistons lowered ambient atmosphere inside by 30" WC. | ||
* So the mean pressure against the gaskets and seals at 1000 RPM (breather valves closed) was 376.63" WC (27.70) Hg or 13.60 PSIA) | * So the mean pressure against the gaskets and seals at 1000 RPM (breather valves closed) was 376.63" WC (27.70) Hg or 13.60 PSIA) |