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Old 02-23-2009, 02:16 PM   #8 (permalink)
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Another reason to go into neutral when coasting: With the clutch in, your wheels are still spinning the output shaft inside the transmission, and also the input shaft and the clutch disk. You have disconnected the clutch disk from the flywheel by pushing in the clutch pedal, but the transmission bits are all still moving. This takes (a little) energy to do.

When you put the transmission in neutral, the input shaft is no longer connected to the output shaft inside the transmission. So you're only spinning the output shaft and its associated stuff, not the input shaft and clutch disk. This takes (slightly) less energy to do than the above, so you will have (slightly) longer glides.

You'll find that a fully-warmed-up engine will usually give higher compression ratings than a cold one, and that removing all of the plugs will also raise the numbers. Make sure your battery and starter are in good shape, too, as those also affect compression pressures. As does your alttiude...

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