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techtalk:ref:engmech04r [2020/10/20 20:18] hippysmack [Measuring Engine Vacuum] |
techtalk:ref:engmech04r [2020/10/20 23:19] hippysmack [Measuring Engine Crankcase Vacuum] |
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| Absolute pressure cannot be lower than absolute zero as that is its zero point. On the other hand, gauge pressure uses atmospheric pressure as its zero point. Even with varying atmospheric pressure, absolute pressure is always definite. Meanwhile, due to varying atmospheric pressure, the measurement of gauge pressure is not precise. Absolute pressure units are sometimes suffixed with the letter “a” whereas units for gauge pressure use “g” as a suffix. ((https://theydiffer.com/difference-between-absolute-pressure-and-gauge-pressure/)) \\ | Absolute pressure cannot be lower than absolute zero as that is its zero point. On the other hand, gauge pressure uses atmospheric pressure as its zero point. Even with varying atmospheric pressure, absolute pressure is always definite. Meanwhile, due to varying atmospheric pressure, the measurement of gauge pressure is not precise. Absolute pressure units are sometimes suffixed with the letter “a” whereas units for gauge pressure use “g” as a suffix. ((https://theydiffer.com/difference-between-absolute-pressure-and-gauge-pressure/)) \\ | ||
| - | ====== Measuring Engine Vacuum ====== | + | ====== Measuring Engine Crankcase Vacuum ====== |
| Engine vacuum is simply air pressure lower than (and is based on comparison with) atmospheric pressure. \\ | Engine vacuum is simply air pressure lower than (and is based on comparison with) atmospheric pressure. \\ | ||
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| Results below are both at 1000 RPM at operating temperature and the test point in each motor was the timing hole plug. \\ | Results below are both at 1000 RPM at operating temperature and the test point in each motor was the timing hole plug. \\ | ||
| From testing in these Sportsterpedia articles; \\ | From testing in these Sportsterpedia articles; \\ | ||
| - | * [[techtalk:ref:engmech04g|Slack tube testing on a 1998 1250S model]]; | + | * [[techtalk:ref:engmech04g|Slack tube testing on a 1998 1250S model]], (elevation app 630 feet); |
| - | * The crankcase pressure had a mean vacuum of 21" of water column (elevation app 630 feet). | + | * 1250cc |
| - | * At 630 feet above sea level, ambient atmosphere is applying app. 29.24" Hg of force (or 397.52 In WC)). | + | * The crankcase pressure had a mean vacuum of 21" of water column. |
| - | * Vacuum created by the pistons lowered ambient atmosphere inside by 21" WC. | + | * 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) |
| - | * So the pressure against the gaskets and seals during operation (breather valves closed) was 376.21" WC (27.67" Hg or 13.59 PSI). | + | * Vacuum at idle created by the pistons lowered ambient atmosphere inside by 21" WC. |
| - | * [[techtalk:ref:engmech07p|Testing with a Slack Tube (Manometer) by bustert]]; | + | * 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). |
| + | * The crankcase cycled from a mean pressure of 13.59 PSIA (idle) to near 14.39 PSIA (5000 RPM) - (range 0.8 PSIA). | ||
| + | * [[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). \\ (both outside in and inside out of a parked engine) | ||
| + | * 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) | ||
| + | * The crankcase cycled from a mean pressure of 13.60 PSIA (idle) to near 14.63 PSIA (5000 RPM) - (range 1.03 PSIA). | ||
| ====== The Effect of Atmospheric Pressure on Vacuum Level ====== | ====== The Effect of Atmospheric Pressure on Vacuum Level ====== | ||
