52 MPG At 70 MPH? No, Not In A Prius--In A Porsche Panamera

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Steady-speed highway cruising doesn't actually take that much energy compared to accelerating up to, say, 70 mph in the first place.

The really hard part is getting consistently high gas mileage in all driving conditions--which is why the 50-mpg Toyota Prius hybrid is still a remarkable vehicle.

Does 52 mpg at 70 mph sound impressive to you?

Well, Mark Phelan of the Detroit Free Press managed to get that level of fuel economy in the 2012 Porsche Panamera S Hybrid he just tested.

(He also tested a Panamera S Turbo; let's just say its twin-turbo V-8 engine did not produce anywhere near that level of fuel efficiency.)

We don't test a whole lot of Porsches around here. The 2011 Porsche Cayenne S Hybrid we drove last summer was a rare exception.

And it confirmed the gas-mileage gains of the Porsche hybrid system, giving us a remarkable 27.7 mpg overall on our usual test route of two-thirds highway, one-third city.

2011 Porsche Cayenne S Hybrid road test, Catskill Mountains, NY, August 2011

2011 Porsche Cayenne S Hybrid road test, Catskill Mountains, NY, August 2011

Enlarge Photo

Porsche has taken full advantage of the VW Group hybrid system it uses in both the Panamera luxury sport sedan and the Cayenne sport-utility vehicle.

Phelan's reading of 52 mpg over 100 or so miles of cruise-controlled 70-mph travel exploited the Porsche system's ability to propel the car electrically at speeds above the legal limit, under light load. Many hybrids only run in all-electric mode up to 30 mph or so.

And as every hybrid driver knows, any time you can shut off the engine (or even shut off fuel delivery temporarily), you save gas.

The EPA rates the 2012 Porsche Panamera S Hybrid at 22 mpg city, 30 mpg highway, for a combined overall rating of 25 mpg.

Which isn't bad for a large, luxurious, high-speed luxury sport sedan--and only goes to show that there's quite a lot of efficiency that can be wrung out of the old gasoline engine yet.

For more on the Panamera S Hybrid and the rest of the model range, see the 2012 Porsche Panamera review on our sister site, TheCarConnection.


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Comments (66)
  1. Oh my goodness. More crappy anecdotal reporting going on again.

    One trip, down hill with a tailwind and good MPG does make kind of a story, it is called a "fantasy." It is usually reserved for the truth-benders on Top Gear, but it is good to see they don't have a monopoly.

  2. @John: If you read the linked article, you'd see that the writer didn't just take an instantaneous reading. He put the car on cruise at 70 mph, and ran almost 100 miles at that speed to get that reading.

    Not sure where you get the "down hill" and "tailwind" bits. The article is as accurate as the piece it's based on, and points out that even large, fast, luxurious cars can get surprising mileage using hybrid systems.

    And, re/"crappy": Watch the language, hmmmm? That's probably within our permissible terms (the filter didn't flag it) but it seems a bit unnecessary.

  3. 1) The comment wasn't necessarily directed at your article but the original reporting.

    2), "this article is as accurate as the piece it's based on" is that part of the standard journalistic due diligence process or are there perhaps other standards that journalist apply from time to time.

    3) "even large, fast luxurious cars can get surprising mileage with hybrid systems," that is really the problem with article. They get cr..., ah make that, poor mileage as the body of your article points out.

  4. (1) OK.
    (2) Not entirely sure what this means. I'm not going to be able to fact-check whether or not the writer did in fact drive almost 100 miles with the cruise control set to 70 mph, or whether he did get the indicated gas mileage. If you know how I could do that, do tell.
    (3) "can" ... the operative word is "can." The article does not say that they all DO. We can agree that most don't.

  5. (2) So if he gets 1000 mpg you will go right ahead and publish without as second thought?
    (3) Sloppy. Any car "can" get 50 mpg under the right conditions, but they "don't" because they are inefficient.

  6. Last round. (2) No, of course not. 1000 mpg is not plausible. A number in the 50s for that car is impressive, on the upper border of plausibility, and hence--IMHO--newsworthy.

    (3) I would be surprised if a Hummer H1 could get 50 mpg under any circumstances at all. Moreover, many people define "inefficiency" quite differently than you do.

    On one hand, there's the argument that anything over 35 mpg doesn't save enough total gasoline to be worth enduring the vehicles it requires. On the other hand, there's the argument that YOU, the Prius driver, are reprehensibly inefficient for hauling around 2 extra seats you don't always use. Get thee a two-seat plug-in or stay home! Etc.

  7. (2) "upper border of plausibility" nice to know that even you are skeptical of the numbers even though you haven't said so until now.
    (3) Just find yourself a little bit of an incline, and don't let the truth get too much in the way of a good story and there you got. Honestly, I hear more of these suspicious MPG numbers from Prius drivers than from anyone else.

    At this point, we don't know what is possible for 35 MPG vehicles, that is, if we insisted on them rather than praising 25 mpg inefficient vehicles.

    As for the two seat plug-in, that is scary, can you read my mind?

  8. 4) The title "suggests" an equivalence of Prius and Panamera hybrid at 50 mpg. This is based on one single, non fact-checked, non-scientific report. The body of the article suggest the actual mpg of the Panamera is HALF that of what is listed in the title and half that of the Prius.

    I don’t care if it is hyper-miling Prius driver claims, 220 mpg Volt driver or whomever, these non-standards based, anecdotal reporting is misleading (if my other adjective is unacceptable, perhaps you will allow this one). The article makes it clear that the number is misleading, so why do it?

    Is it the joy of the “man bites dog” ironic headline?

    Do you want to believe it, even though you know it is misleading?

  9. (4) I would argue that the title suggests that readers may assume that a Prius is the ONLY car that can achieve 50 mpg *under any circumstances*.

    To me, it highlights a positive accomplishment: better fuel economy (under certain circumstances, which I describe) in a seemingly unlike car.

    I'm a bit puzzled why this seems to outrage you so.

  10. It is a parlor trick, an attention grabbing headline, misleading the public into believe things that are not true, and trivializing the auto-manufacturers that have taken the problem to heart and actually produce fuel efficient vehicles, e.g. Ford, Honda, Toyota.

  11. Yes, John, occasionally I write headlines designed to lure people into reading the damn stories. Sorry about that.

    Do tell what headline you'd propose instead.

  12. The truth.

  13. There are more comments in this thread
  14. Should we be impressed that Porsche’s engineers (some of the worlds finest) have developed a 25 mpg vehicle that costs $100,000? Or is it sideshow circus freak of the green car movement.

    Headlines have a life of their own, e.g. Prius does more environmental damage than Hummer, no matter if they are really baseless claims or tempered in the body of the article, the damage is done unless the headline reflects the reality of the situation.

  15. And, frankly, you need to understand that people who shop for a Porsche Panamera are NEVER going to cross-shop it with a Prius. Yes, the Prius gets 50 mpg. Yes, the Panamera "only" gets 25 mpg. But the alternative to the Panamera is a host of equally expensive cars that get more like 15 mpg--so its impact on gallons of gasoline saved every 1,000 miles is higher than that of a Prius replacing, say, a 33-mpg Corolla. (Although of course many more Priuses than Panameras are sold, so the impact evens out.)

    In the end, I can't help wondering if you simply disapprove of the idea that anyone is buying a car with lower fuel efficiency than a Prius?

  16. We are fortunate to have a government that has set standards for passenger cars for fuel efficiency. Let's see how Panamera stacks up against the "average" fuel efficiency the government requires.
    2025, 54.5 mpg, Panamera less than half
    2016, 37.8 mpg Panamera fail
    1985, 27.5 mpg Panamera still fails

    By what objective standard is a 25 mpg car considered to have impressive gas mileage in 2012?

  17. As for cross-shopping, want to bet? Neighbors with BMW's got rid of them for Prius and Nissan LEAF. Other neighbors with an SUV now let it collect dust and drive a Prius. Does that blow your world view? or do you understand why they are doing it?

    Lab director with an M5 wants a Model S instead.

    As for the goal of having everyone drive a vehicle with the efficiency of a Prius, I would never settle for a goal with such low efficiency. Not only can we do better than the Panamera, we can do better than the Prius. Much.

  18. First--as you know perfectly well (since we've covered it many times here)--54.5 mpg in CAFE mileage translates to low- to mid-40s on the EPA window sticker.

    Second, we return to the idea that you apparently will never tolerate ANYONE not driving the MOST efficient car in the market, your beloved Prius. And that's at a minimum, per your second comment.

    Which is a fine opinion to hold, but I fear the auto market doesn't work that way. We report here on what IS, not what one reader believes SHOULD BE. We are reporters, not advocates. See here:

  19. There are more comments in this thread
  20. "Phelan's reading of 52 mpg over 100 or so miles of cruise-controlled 70-mph travel exploited the Porsche system's ability to propel the car electrically at speeds above the legal limit, under light load"... so this car has a big battery and a plug? There is no way a regular hybrid could boost average MPG over that distance to that level at highway speeds without sustained electric support from an outside source. Weird story...

  21. It was written in a web article with no way of verifying it so it must be true.

  22. @Chris: Why so? As I noted to Mr. Briggs, I did not independently verify the claims in the newspaper article, but on flat roads like those in Michigan, keeping a (relatively aerodynamic) 4,300-pound car moving at the same speed consumes only a fraction of its maximum power. The electric motor in the car is 34 kilowatts (46 hp) and that may well be enough to propel the car at steady speed on flat roads.

    When that engine can switch off at times and the car can "sail" on battery power--as we observed our Cayenne S Hybrid doing at times--then doubling the rated EPA overall mileage of 25 mpg is plausible.

  23. I have to repeat the question: where would the energy come from? A regular Panamera would probably get less than half that mileage at highway speeds over 100 miles, so the electric motor will have to do a lot of work, all fueled by some energy recuperated while breaking in an earlier phase of the trip? Because that's where the savings lie for non plug-in hybrids; they only happen in city driving, there is no reason why highway driving should be more efficient than the non hybrid version. That makes the 52MPG claim over a 100 miles at 70MPH rather fishy at best and I completely understand John Brigg's annoyance with this article.

  24. @Chris, thanks for the help.
    The added efficiency on the highway of the hybrid system in the Panamera comes from using the engine at a point of higher efficiency.

    Let's assume the non-hybrid loads the engine at 10% all the time. Then lets assume that the hybrid loads the engine at 20% but only for half the time. Half the time the engine is driving the wheels and charging the battery. The other half of the time, the battery drives the wheels.

    But loading the engine at 20% for half the time, is more efficient then loading the engine 10% all the time. It is about getting the ICE to operate more efficiently when it is on, and then turn it off.

    Still 52 mpg is at the "upper limit of plausibility".

  25. And the winner for the most inefficient hybrid car is...
    oh dang it, I was so hoping it would be the Panamera, oh well
    1) BMW Activehybrid 7, 20 mpg
    2) Lexus LS600, 20 mpg
    3) Porsche Panamera 25 mpg

    So among the hybrid cars, Panamera ranks 21 out of 23.

  26. OK, fair enough. But not quite clear what the takeaway is here. So I shouldn't have written about it at all? Or I should have written an angry article denouncing a large, pricey luxury sport sedan for not being as efficient as a Toyota Prius?

  27. Vehicles like this don't really deserved to be "talked-up" as if they are green vehicles. Surely someone that can afford a $100,000 vehicle can find something more fuel efficient than this that is acceptable.

    And the story probably should not have been written at all with the dubious data source as its basis.

  28. @ John Briggs, settle down. I think you've set your standards WAY to high for green vehicles. Most of the cars you criticize are only in their fist generation, you should simply be happy that Porsche is onboard with the hybrid and electric car revolution instead of holding them to a standard you've set in your mind. I was guilty of that for a while, I thought since the Prius could manage 50mpg that all hybrids should get 30mpg city and up. But I realized that all car companies have to do things their own way and they are all going to have to start somewhere. We've got to give it some time to grow, the only reason the Prius is so good is that it has had time to improve through a few model generations.

  29. In my experience, cars like the Prius and the Porsche Panamera only exist because the car company executives have set aggressive goals and applied excellent engineers to the problem. In the case of the Prius, that goal was efficiency in a vehicle well sized for a family of four with reasonable performance at a reasonable price point. They have succeeded.

    In the case of the excellent Panamera, the goal was performance, and the company achieved that for sure.

    Now we come down to the consumers and the reviewers. Shall we set high goals and expectations? or low ones? What types of goals do we wish to achieve? What will success look like? What type of shape will we leave the planet in? the country in? What do we want to optimize?

  30. @John Briggs: "Surely someone that can afford a $100,000 vehicle can find something more fuel efficient than this that is acceptable."

    A Model S, for example. But the author prefers to push hybrids, I think. ;)

  31. The 2012 Tesla Model S obviously one competitor to the greener end of the Panamera range. And as soon as it becomes a real production vehicle and we've had a chance to drive it, we'll add it into the mix.

    But at the moment, the Model S is not a production car. No one's driven one, the lines are not building cars for sale to the public, and deliveries are still several months away.

    And as recent history shows us, many new electric cars get announced, or even go into production, only to meet a sad end.

    I think Tesla's chances of putting the Model S into volume production and broad sale are now better than 50-50, but I don't consider it a real car. Yet.

  32. @John. Better than 50-50? I'd put the chances of Model S coming to production at close to 100%, at this point. It sounds like you seem to have a lot of doubts. I wouldn't know where they might come from.

  33. I think at this point I believe that Tesla will get cars out the door sometime by the end of this year. But the Fisker Karma provides one case study of the kinds of things than can go wrong with a new car from a new and marginally capitalized car company.

    Tesla is now better capitalized, post-IPO, for sure, and it has experience from the Roadster to guide it. That's why I say "better than 50-50" chance.

    Still, many a slip 'twixt cup and lip ... and getting a car into production at all, and ramping it to volume + selling it broadly over a matter of years are two different things.

    I hope Tesla succeeds in doing that. But the only way they will convince their skeptics is...doing it.

  34. There are more comments in this thread
  35. If you are saying the 100 mile feat was done using the battery, and it is *not* a plug-in, then the battery was charged from the gas motor, previously, and that gas was not included in the numbers.

  36. The car was powered primarily by the gasoline engine, of course.

    But at times, I presume the engine switched from powering the car to recharging the battery. (The VW Group single-motor hybrid system can't do both at the same time, unlike the twin-motor system used by Toyota.) Once the pack was charged, under light load, the engine can switch off completely and the battery and motor alone can propel the car for a while. Then the cycle repeats.

    I observed this in the Cayenne S Hybrid we tested, and I have no reason to believe the Panamera S Hybrid wouldn't operate in the same way.

  37. Sure, but this is what all hybrids do. 70 mph is close to the optimal load (usually around 80 mph, I think, but not sure) of a gas engine, so I'm not sure driving at 70 mph, just 10 mph less, gives much room for improving efficiency by optimizing load through a hybrid cycle. Another explanation seems necessary. Maybe extraordinary good aerodynamics? Optimized engine tech? I don't know.

  38. The first sentence in my last post wasn't expressed well. Hybrids aren't usually able to turn off the ICE at highway speeds (though of course at lower speeds). However they use smaller engines to match the smaller optimal load of the engine with the load of driving at highway speeds.

    Would a larger engine, running part of the time, be more more efficient than a smaller engine, also running at its optimal load, but all the time?

    I'd rather think that some juice was left in the battery from previous driving, and/or that John Briggs info about auto shut-off imprecision might explain it.

    50 mpg at 70 mph seems pretty far from EPA 30 mpg highway rating, to me. Or its some unusual explanation. Like wind. ;)

  39. @Norbert: Further discussion with author Mark Phelan points out how little power it takes to keep a car moving at steady speed on a flat road.

    He wrote: "My favorite example of how little energy steady-state requires was in a 1001-hp Bugatti Veyron convertible. There's an analog gauge that shows instantaneous hp output. At 70 mph...it was about 60 horsepower."

    I'm quite willing to admit that his number may be off. Instead of 52 mpg, it might be 47 mpg--or 55 mpg.

    But the point of the article remains: You can get remarkably high highway cruising mileage in unexpected cars, including a large, fast, luxurious full-size sport sedan like the Panamera using hybrid technology.

  40. Left over juice in the battery can have some impact. Sometimes the Prius ends up fully charged at the end of the day, particularly if just prior to parking, it came down a long hill.

    However, I don't think the Porsche would get more than a few miles on the 1.7 KWH battery in the Panamera and Mark did travel 100 miles. So this error would likely be only a percent or two.

    The much greater opportunity is in the filling process. It is for this very reason that MPG is typically reported after multiple tankfuls of gasoline are used. This reduces errors and gives feedback on the measurement process (error bars?).

    In this case, only one tenth of a tankful was used which significantly increases uncertainty.

  41. While it is impressive that due to its aerodynamic design, Bugatti takes very little horsepower to push it down the road, it is still very inefficient due to its large engine running at very light loads. This largely explains the Bugatti's 10 mpg EPA rating. This puts it clearly in the "gas guzzler" category according US government definition. So I don't think this does much to support Voelcker's and Phelan's claims.

    Regarding the 52 mpg Porsche

    "extraordinary claims require extraordinary proof"

  42. There are more comments in this thread
  43. Actually I didn't know that the Panamera and Cayenne hybrids behave like serial hybrids under some circumstances, and that is in fact different from most other non plug-in hybrids. Still Volt EPA rating for gas powered miles isn't particularly impressive so I doubt using an electric motor rather than a mechanical transmissions has any real beneficial impact on mileage and therefore this doesn't help to make the 52 MPG myth more plausible.

  44. Mark Phelan was kind enough to give more details on how the 52 MPG was determined.

    Mark drove 100 miles, put 1.92 gallons into a 21.1 gallon tank relying on the accuracy of the auto-shutoff at the pump to come up with the 52 mpg figure. Let's consider the air bubbles in the tank, how full the tank was when he started, the inter-instrument repeatability of the auto-shut off measurement of multiple pumps. The error bars on that experiment are huge.

    This is why you should not pay too much attention to automotive journalists. After all the criticisms of the EPA mpg process by automotive journalists, too bad there isn't some self reflection.

  45. Hmm...I think John Voelcker owes it to his readers at this point to get his hands on a Panamera Hybrid and repeat the experiment. After all he does want us to believe that after more than a century of development the old ICE still has a lot of scope for efficiency improvement left based on these numbers. If he really gets 52 MPG at 70MPH over 100 miles in a big heavy car like the Panamera, I'll believe him. Until than...not so much.

  46. 1st time i drove a prius 3rd gen was a 120mile highway trip. Avg 58mpg. So, 58mpg in a prius at 65-70mph? YES

  47. The biggest question is: are enough Panamericas sold to warrant creating a hybrid? The non-hybrid Panamericas are gas guzzlers, but so few of them are sold that it really doesn't make any difference in the grand scheme of things. I guess people that can afford them need a feel-good car, too.

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