You Probably Don’t Realize How Inefficient Internal Combustion Engines Are

One of the most frequent focuses of discussion between electric vehicle adopters and their critics is range. The usual argument is that fossil fuel vehicles can do 700 miles between refuels and take five minutes to do so. But the range focus hides a very important feature of battery-electric cars – they are much more efficient than internal combustion.

To illustrate this, we need to do a little calculation. This is made more complicated than it could be because of the different ways specifications for internal combustion vehicles and battery-electric ones are stated. For the latter, you almost always know the battery capacity and nominal range. For fossil fuel cars, you might not even know how big your tank is, just the nominal miles per gallon. Range isn’t usually part of the specification. You almost certainly have no idea how much energy that equates to per mile.

When you work things out so they are comparable, however, the amount of energy an internal combustion engine car uses compared to a battery-electric one becomes starkly contrasted. This particularly sprang to mind for me when I realized that a car I used to own – a 1992 classic Porsche 968 – had about the same range on a “full tank” as the car I replaced it with – a Tesla Model 3 Performance. Both do a little over 300 miles from full to empty. The Porsche could do a bit more than that if not driven the way a Porsche should be, but this is all “back of the cigarette packet” calculation, except that I stopped smoking a few decades ago.

I’m going to use slightly different cars for this article and base the calculations on EPA and WLTP figures to keep things as fair as possible. The cars I’ve chosen are the Tesla Model 3 Long Range for BEVs, and the Toyota Camry to represent the fossil corner, as it was America’s bestselling car in a similar class to the Model 3 and globally available, albeit not in the UK since November 2021. The Camry can be purchased as a hybrid now, so more efficient than combustion-only versions, but it will still make the point clearly.

Let’s start with the Tesla. The current Model 3 Long Range has an 82kWh battery, delivering 374 miles of WLTP range or 358 miles according to the EPA test. That equates to 4.6 miles per kWh (WLTP) or 4.4 miles per kWh (EPA). The 2.5L Camry LE Hybrid delivers 53.3mpg (that’s British gallons) according to the WLTP test, and 52mpg (American gallons) according to the EPA test. But how do we convert that to kWh for comparison?

Nobody really talks about how much energy is in a gallon of gasoline (or petrol, as we call it here in the UK) in these kinds of debates. But you can track this figure down quite easily. One figure I found was 9.6kWh per liter, which equates to 43.58kWh per (British) gallon. The usual measure is “Gasoline gallon equivalent”, from which MPGe (miles per gallon of gasoline equivalent) is derived. The E10 version of gasoline / petrol comes out at 32.78kWh per (American) gallon, according to the US Environmental Protection Agency.

The next thing we need to figure out for the Camry is how many kWh it takes per mile, so we need to pump those figures into the MPG we obtained before. Using the WLTP MPG figure and the British gallon energy value, you get 1.2 miles per kWh. Using the EPA MPG and gallon energy value, you get 1.59 miles per kWh. So via the WLTP efficiency rating system, the Camry uses 3.74 times as much energy as the Tesla per mile, and via the EPA rating, 3.57 times as much. Where does the rest of the energy go? Wasted heat, friction in the drivetrain, and other inefficiencies.

Of course, this isn’t to say that a gallon of gasoline / petrol uses so many more kWh of electricity. It will use some during its production process, but the oil had that energy potential already when it was extracted from under the ground. The point I’m trying to make here is that an internal combustion engine uses up way more energy per mile than a battery-electric one. So much that it’s not even in the same ballpark. Why are we wasting all this energy when we don’t have to?

Sure, internal combustion currently has some practical advantages – longer-range vehicles, cheaper vehicles, quicker to refuel. But it is fundamentally a worse technology than battery-electric vehicles. It has been around for over a century, and its efficiency has only improved a little during this time. We can ill afford to be throwing so much energy away when an alternative is available that can deliver so many more miles per unit of power. This is why phasing out internal combustion for everyday transportation is so important.