Gears and MPG
#1
09-20-2011, 08:07 PM
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#2
09-20-2011, 08:52 PM
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hers sum help give yea the idea of what rpms and ****,
fil out the info do calculate and then at the bottom is the highway speed thing should help give ya idea of what rpms ya turnin
http://www.grimmjeeper.com/gears.html
fil out the info do calculate and then at the bottom is the highway speed thing should help give ya idea of what rpms ya turnin
http://www.grimmjeeper.com/gears.html
#3
09-20-2011, 10:52 PM
Champion
The part that confuses the issue is engine load... The lower gears will cause less load on the engine, which improves economy, as counter intuitive as it sounds...
Think like this: your running highway speeds, pushing your 5.5k# truck at 60mph, through overall drive ratio of 2.75, and engine rev of 1600rpm, pulling 12 bars of vacuum.. let's say the world is perfect, and altitude, barometer pressure, wind value, changing elevation isn't an issue.. once you achieve a set speed/rpm/vacuum, it won't change much.. your engine basically operates like a stationary generator would.. it hits a speed and it doesn't change.. the engine could trim the fuel to perfection in timing and fuel delivery.. your mileage would be floggin awesome..
The world isn't perfect.. least I ain't found a perfect place, and I've been looking..
If you're trying to achieve speed you're dumping more fuel than your burning until it catches up.. when it catches up, it planes off..
Guess what helps you achieve that 'plane' quicker? .... Gearing..
If you reduce your ratio, and alter the overall drive ratio to something like 3:1 as opposed to 2.75:1, you'll run higher RPMs, but you'll decrease the time your drawing excess load/vacuum on the engine.. you're economy will increase.. a lot..
The ratio/rpm model that makes a science out of distance traveled/revolutions and attempts to compare to engine displacement and RPMs goes out the window in real world conditions..
So long as you don't go crazy and run something silly low, and you keep your foot out of it, around town and moderate highway, you'll increase your mpg's... The only time the lower gears will hurt you is on a long haul at a steady speed over unvarying terrain at unvarying elevation.. do you know of such a place? I do, but I don't go there often.. or, at all as it is..
Overall ratio is the important one.. when you bump to 35" tires, you'll likely be just slightly lower than you are now with 3.55:1 and 31".. overall ratio is the important one..
Think like this: your running highway speeds, pushing your 5.5k# truck at 60mph, through overall drive ratio of 2.75, and engine rev of 1600rpm, pulling 12 bars of vacuum.. let's say the world is perfect, and altitude, barometer pressure, wind value, changing elevation isn't an issue.. once you achieve a set speed/rpm/vacuum, it won't change much.. your engine basically operates like a stationary generator would.. it hits a speed and it doesn't change.. the engine could trim the fuel to perfection in timing and fuel delivery.. your mileage would be floggin awesome..
The world isn't perfect.. least I ain't found a perfect place, and I've been looking..
If you're trying to achieve speed you're dumping more fuel than your burning until it catches up.. when it catches up, it planes off..
Guess what helps you achieve that 'plane' quicker? .... Gearing..
If you reduce your ratio, and alter the overall drive ratio to something like 3:1 as opposed to 2.75:1, you'll run higher RPMs, but you'll decrease the time your drawing excess load/vacuum on the engine.. you're economy will increase.. a lot..
The ratio/rpm model that makes a science out of distance traveled/revolutions and attempts to compare to engine displacement and RPMs goes out the window in real world conditions..
So long as you don't go crazy and run something silly low, and you keep your foot out of it, around town and moderate highway, you'll increase your mpg's... The only time the lower gears will hurt you is on a long haul at a steady speed over unvarying terrain at unvarying elevation.. do you know of such a place?
I do, but I don't go there often.. or, at all as it is.. Overall ratio is the important one.. when you bump to 35" tires, you'll likely be just slightly lower than you are now with 3.55:1 and 31".. overall ratio is the important one..