Increase Your Gas Mileage by 41%, No! Wait!! By Over 63%

Last month I wrote an article about how you can increase your gas mileage 41%.  I'm here to report that this figure was grossly inaccurate.  The truth is, you can actually increase your gas mileage by over 63%.  I know this because I have done it, reliably.  As I learn more techniques and tips, my gas mileage just keeps getting better and better.  Achieving such dramatic efficiencies in a normal internal combustion engine does not require doing anything drastic, dangerous or illegal.  There are some people that use more"shady" techniques like drafting off of semi trucks.  While this may increase their fuel economy, it is illegal, dangerous and doesn't reduce the environmental impact of burning fossil fuels.  It merely passes the costs of fuel from the drafter to the truck driver. 
I was able to increase my performance an additional 22% (above the 41% I was already achieving) for a total of a 63% increase.  This latest 22% requires installing a tool that provides instant feedback about how driving style is effecting the fuel economy and changing your driving style to attain maximum fuel economy.  Instant feedback is the key to such dramatic fuel savings. 
One such tool is the vacuum gauge.  It will work on any vehicle, costs you less than $30 yet it will save you hundreds at the pump. 

The Vacuum Gauge that I installed in my 1992 Honda Accord displays a vacuum pressure ranging from 0 to 30 Hg (inches of Mercury).

The gauge's vacuum hose connects to the extra port on my intake manifold. How convenient that there was an extra port. No cutting or splicing involved.

Vacuum pressure at the intake manifold is loosely correlated to fuel efficiency.  The harder you push on the gas pedal, the lower the vacuum pressure and the more gas your vehicle will consume. For my car, the gauge displays 0Hg at full throttle and as high as 24Hg when it is coasting in gear.  My car gets much, much higher gas mileage when I drive in a manner that keeps the vacuum pressure as high as possible.  Typically this is in the 12-18Hg range. 
Cruising on the freeway I can maintain a vacuum pressure of 15Hg.  The vacuum gauge also doubles as an inclinometer.  Driving up a hill (like an overpass) while maintaining a constant speed, the vacuum gauge will drop down toward 10Hg.  Driving down the other side, the gauge jumps up toward 20Hg. 
By driving so that the vacuum gauge remains at a constant vacuum pressure, your speed may fluctuate, your acceleration will be smaller but your fuel efficiency will be much, much higher. 

From last week's blog post, we learned that when a vehicle is driven at a low engine RPM, fuel economy goes way up.  But pushing too hard on the gas pedal while in an upper gear will bog the engine down, potentially negating any fuel savings (automatic transmissions don't suffer from this but they don't get as good of fuel economy either). 
Fortunately, the vacuum gauge will indicate if you are bogging the engine or not.  If you are cruising along a 30mph street in 4th or 5th gear, with very little throttle, the vacuum gauge will still display a nominal value.  But even an unnoticeable increase in throttle position will bog the engine down and kill the vacuum pressure at the intake manifold, increasing fuel consumption.  Having this feedback is key to driving at the lowest possible RPM while still preventing bogging and preserving fuel efficiency. 

For vehicles newer than 1996, the superior version of the vacuum gauge is the Scan Gauge II. 
Not only does the Scan Gauge calculate and display dozens of parameters like miles per gallon, gallons per hour, total trip cost, closed loop status and engine temperatures, it can also be programed with vehicle specific gauges for your particular vehicle.  For example, for my wife's Chevy Venture, it will display horse power, engine torque, air/fuel ratio, transmission temperature and even an obscure parameter called “knock retard”, (how many degrees of ignition time advance must be removed to compensate for low octane fuel, thus preventing engine knocking).  For hybrid vehicles, the Scan Gauge will display "state of charge" and the regenerative charge rate of the battery system. 

Efficient driving habits will save you money at the pump in exchange for a slight increase in commute time. 

For me, slower acceleration and reduced cruising speed adds 3 additional minutes to my 20 mile commute.  In exchange, I only have to pay to fill up for gas tank every 4 weeks instead of every two and a half.  Not a bad compromise in my opinion.