Quote:
Originally Posted by oil pan 4
Idle is typically 14 to 15 inches of Mercury.
Driving on the highway you can see up to 21 inches of mercury.
My friend has a 4 cylinder Tacoma, when he goes up hills he leaves it in top gear as long as possible. Very low vacuum show much better mpg on the scan gauge then shifting it in a lower numbered gear, more RPMs and more manifold vacuum like you tend to get with an auto transmission.
Ideally you would have a 1L engine and something like a 7 or 8 speed manual transmission and put it in the highest gear you can maintain speed and hold the gas on the floor.
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Depends on car and engine. Usually lower RPM helps with cruising MPG by reducing friction and pumping losses. However in my case I have noticed I get better mileage avoiding areas between 1000-1700 RPM. my mileage peaks at 1900 rpm or 45mph in top gear and drops off going higher or lower. So sometimes when I'm accelerating I try to avoid top gear unless it will drop me at or above 1900 rpm or unless I'm ready to cruise. For pulse and glide I also avoid engine speed lower than 1800-1900. I find some vacuum to avoid enrichment and moderate engine speed (1.9k-2.5k rpm) to be best for efficient acceleration or p&g. I just get up to speed faster due to much higher available horsepower at or above 2k rpm and I can drop to neutral and coast for much longer sooner where it really helps my trip mileage.