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techtalk:ref:engmech07e [2020/10/02 22:02] hippysmack [Further Study of Internal Engine Pressure] |
techtalk:ref:engmech07e [2020/10/02 22:24] hippysmack [Further Study of Internal Engine Pressure] |
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| * Better oil scavenging and keeping down pumping loss at high RPM. \\ 76< engines breath and scavenge from the same hole. \\ They may be more sensitive to wetsumping than later models because of this. The air can't jump ahead of the oil to the rotary breather. \\ Oil is thicker and doesn't compress. What does that do to air pressure behind it? \\ 77> engines breath and scavenge from different holes. \\ Makes for a more free flowing internal system. | * Better oil scavenging and keeping down pumping loss at high RPM. \\ 76< engines breath and scavenge from the same hole. \\ They may be more sensitive to wetsumping than later models because of this. The air can't jump ahead of the oil to the rotary breather. \\ Oil is thicker and doesn't compress. What does that do to air pressure behind it? \\ 77> engines breath and scavenge from different holes. \\ Makes for a more free flowing internal system. | ||
| - | We know downstroke pushes oil toward the oil pump. \\ | + | We know downstroke pushes oil toward the oil pump. Excess vacuum slows that process, can back up oil and cause wetsumping. \\ |
| - | Excess vacuum slows that process, can back up oil and cause wetsumping. \\ | + | |
| But, if the underside of the pistons are slight negative, it helps the rings seat without as much vibration and turbulence. \\ | But, if the underside of the pistons are slight negative, it helps the rings seat without as much vibration and turbulence. \\ | ||
| As a rule, rings sit on their own springiness when pistons go up and are forced against the wall by the combustion pressure that is allowed to pass behind them. ((thefrenchowl of the XLFORUM http://xlforum.net/forums/showthread.php?t=2077771&page=6)) \\ | As a rule, rings sit on their own springiness when pistons go up and are forced against the wall by the combustion pressure that is allowed to pass behind them. ((thefrenchowl of the XLFORUM http://xlforum.net/forums/showthread.php?t=2077771&page=6)) \\ | ||
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| Upstroke is not affected as much until after vacuum starts to build. \\ | Upstroke is not affected as much until after vacuum starts to build. \\ | ||
| - | The 57-76 timed breather doesn't close on BDC but rather farther upstroke. \\ | + | The 57-76 timed breather doesn't close on BDC but rather farther upstroke. \\ |
| + | It presets how much vacuum the pistons are allowed to create and how long they have to expel air pressure.\\ | ||
| So the rising piston isn't hindered by vacuum until after mechanical and perpetual motion has been exerted on the it. \\ | So the rising piston isn't hindered by vacuum until after mechanical and perpetual motion has been exerted on the it. \\ | ||
| In in 76< engines, you are limited to what air you can expel thru the breather gear before upstroke happens with the gear still open. \\ | In in 76< engines, you are limited to what air you can expel thru the breather gear before upstroke happens with the gear still open. \\ | ||
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| In contrast, the 77-up breather closes when the last piston is at bottom dead center (BDC). \\ | In contrast, the 77-up breather closes when the last piston is at bottom dead center (BDC). \\ | ||
| - | Is that extra vacuum taxed to the piston? | + | Is that extra vacuum taxed to the piston? \\ |
| The better the gaskets and seals, the more vacuum you can run. \\ | The better the gaskets and seals, the more vacuum you can run. \\ | ||
