Ask Pablo: Could a Hacked Hummer H3 Really Get 60 MPG?

Dear Pablo: Is it true that a hacked Hummer H3 could achieve 60 miles per gallon?

There are plenty of claims out there from people promising amazing fuel economy. Some of these claims are based on technology, while others are based on behavioral changes like "hypermiling" driving techniques. Let's take a look at where this particular claim comes from and then figure out if it is even theoretically possible without attaching a sail to the roof or installing pedals.

The reader's notion that a Hummer could be converted to achieve 60 mpg come from an post on Gas 2.0, which references a 2007 Fast Company article which does indeed quote the designer, Johnathan Goodwin saying "it'll get 60 miles to the gallon." Autobloggreen.com and various other blogs and news outlets picked up on Johnathan Goodwin's work in 2007.

The concept being developed was a 2005 Hummer H3 powered by electric motors that were supplied by a biodiesel-powered micro-turbine and a bank of super-capacitors. In addition to getting 60 miles per gallon, this car would also have "2,000 foot-pounds of torque" and the ability to do "zero to 60 in five seconds." This combination of performance specs, along with the vehicle's 5,000 pound weight does not seem plausible. So, is it possible?

So, How Did The 60 MPG Hummer Turn Out?

Since 2007, coverage of Johnathan Goodwin and his work on the H3 has been mysteriously silent. The website of his Hummer conversion business, H-Line Conversions, has not been updated since then either. A Daily Kos article suggests that he is a fraud but there is not much more information available on the success (or failure) of his 60 mpg Hummer H3. However, in 2010 a team including Johnathan Goodwin and Neil Young converted a 1959 Lincoln Continental Convertible with a 30 kW Capstone microturbine, a 150 kW Prime Mover electric motor, and a series of batteries (The car was damaged in a fire but is being rebuilt). This car weighs 6,200 pounds and is said to travel 50 miles, running on purely electric power from the batteries, and another 350 using the microtrubine.

OK, So Is It Possible To Get 60 MPG In A Hummer H3?

A typical internal combustion (IC) engine has a maximum thermodynamic efficiency around 37%, meaning that no IC engine can ever be built that is more efficient. However, conventional engines are more like 18-20% efficient. Microturbine efficiencies are typically between 25% and 35%, almost twice that of the internal combustion engine. So, with 15 mpg and an engine efficiency of 19%, the modified H3 should get around 27.6 miles per gallon (assuming the most efficient microturbine). The modified H3 also has efficiency losses in the capacitors and electric motor, so the fuel economy would probably not exceed 25 mpg. Add regenerative braking and the fuel economy might reach half of the claimed 60 mpg.

Generally if something sounds too good to be true, it probably is. Unfortunately this is no more true than it is for fuel economy claims. What is even more unfortunate than a designer's inflated claims is that media outlets propagate these notions without first doing some simple calculations. A gallon of gasoline contains a terrific amount of energy, 28,747 calories to be exact, but there is little chance of it taking a 5,000 pound vehicle 60 miles.