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Old 5th Jun 2017, 12:55
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horizon flyer
 
Join Date: Nov 2005
Location: UK
Age: 77
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B2N2 Just the laws of physics. The exhaust stroke empties the cylinder of gas the induction stroke increases the volume in the cylinder to be filled by air pressure if the throttle is closed very little incoming air so the bottom of the piston has to push against air pressure as it pulls a vacuum in the cylinder. If the throttle is wide open then the pressure across the piston is almost equal on induction and just the pumping losses in physically moving the air. On an already spinning engine the compression force is supplied by the flywheel and any other piston on its firing stroke in a running engine, note a 4 cylinder 4 stroke has only 2 firing strokes per rev and the prop drives the engine 30% of the time that's why 6 cyl are better. When the piston gets to the top of stroke any stored gas pressure will push the piston down so recovering most of the compression energy, so less pumping losses with the throttle wide open, thats one reason why the best altitude to cruise at is at throttle wide open at cruise power.

This can be confirmed on old cars with key ignition and push button start. Both feet on the floor key off no choke spin the engine, note turnover speed, gently press the accelerator to the floor spin the engine on starter motor once over the first compression it will spin faster due to lower drag. Warn wait before starting as exhaust can be full of fuel and explode if not given a few minutes. I have used this method to move a car with a stalled engine, just put it in first gear floor accelerator slowly turn over with starter and it will move good for 50 feet to get out of danger.

Note in physics there is no such thing as suck.

So no black magic just an understanding of physics.

Last edited by horizon flyer; 5th Jun 2017 at 15:04.
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