Hypermiling a Boxster!

Yes, yes - I realize that it is akin to sacrilege to even attempt such a thing, but today on my way to work (after having my battery disconnected the other day, so the mpg numbers were reset), I thought that I'd give it a shot to see what I (and the car) could manage. My commute is roughly 10 miles each way, all on surface streets. Moderately busy traffic. Max posted limit on any of that stretch is 45mph, and there are lots of stop-und-go lights along the way. Thanks to construction season (this is the Chicago area, if you're familiar), I spend some of the trip on residential streets with an array of stop signs to make things fun. Normally my indicated economy numbers are 20-21 mpg (though that's at least 1 mpg better than my fill-up calculations). Normally I don't drive especially hard or fast, but I don't dawdle, either. On the 45mph section I will hit 60 if traffic and the local gendarmes allow it. Hearing the engine sing is one of the great joys of driving this car. Today I threw "normal" out the window and granny shifted every gear. If the shift arrow went on, I upshifted. 1st gear was just to get the car moving enough to get it into 2nd. At the same time, I did not make a nuisance of myself by getting in anybody's way. It wasn't the most fun drive that I've ever had, but at least the top was down, and it was a beautiful afternoon. Before I shut the engine off after getting home, the display read 25.1 mpg. At one point on the morning run, it briefly said 25.5. I won't say that I was shocked, but I am somewhat pleased. One of these days, I'll take it on a long trip and see how it does without all of the traffic control that semi-dense suburban living provides.

That startup (engine cold) is brutal on fuel economy. I often reset the MPG readout to see how I can do on a drive. After car is warmed up, slow stop-and-go can be 17 MPG, but with a cold car (and it's not even very cold here in California), the first 5 miles average 12 to 15 MPG. On the highway I've seen 26 on the low side and 31 on the high side. The 31 was highway driving with lots of other traffic, which kept speeds moderate (65 to 75) and gave me a little bit of drafting. I'm not a tailgater and try to keep following distance just barely close enough to keep me from getting cut off all the time. I've noticed that air temperatures 80+ degrees (farenheit) help due to lower air density even if I run the A/C. I believe that the most detremental mileage design is the low gearing of 6th gear. For the 987.1 CS, I'm doing 3200 RPM at 80 MPH. That should probably be 2500 RPM. The gear ratios betwen 3-4, 4-5, and 5-6 are 20% or less. They should probably be about 30 to 35% each.

Very interesting experiment that you've conducted there. Apart from changing your shift points , did you find that the more relaxed approach altered other aspects of your driving such as your braking behaviour e.g. because it took longer to get to speed then perhaps you were braking more conservatively in order to keep the car rolling? Were you applying the throttle more smoothly at lower engine speeds? If so, then that may also have contributed to better fuel economy. I disabled the upshift indicator using my ThinkDiag not only because I prioritise performance and driving enjoyment over economy, but mainly because I felt deeply uncomfortable with what I was doing to the engine if I'd taken notice of it - making it "lug" instead of spinning freely where it was operating at its happiest. I couldn't believe that Porsche engineers would encourage loading the engine up like this by having the upshift indicator activate at such low engine revs.

I pretty much never look at or reset my MPG

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I'm sure that it is, but I love the sound. Startup/growly idle only lasts a minute or so for me.

I always try to conserve momentum to whatever degree that I can in normal driving... eyes on the next set of lights, don't tailgate, etc.. I didn't really change that for this little experiment. For what it's worth, the engine never seemed unhappy at the shift points that the car recommended - just pretty gutless. It was just a bit surprising that I managed to get circa 4 mpg (indicated) better than normal. I doubt that I'll become a hypermiler, though - none of my small fleet of cars is really set up for it. It also doesn't match up with my idea of fun.

Best fuel mileage I recently achived on mine was 10.9 L/100KM...21 MPG.Mostly highway, but was not nursing it much. If I am on my daily commute, stop and go Toronto traffic...I am at around 14.5 L/100KM...16 MPG.

I have yet to do any extended highway driving in my Boxster. 16 mpg just sucks, though! That about matches what I used to get in the '83 Rx-7 I had for a couple of years. Lightest car that I've owned (I think), and it got about 16 mpg. But it was fun!

my 2008 Cayman S gets ~24 mpg on extended highway driving (e.g. driving from San Francisco to Los Angeles), more typical driving it gets 16-18 mpg.

For what it’s worth I have achieved 38 US mpg (6.2 l/100 km indicated) on a country run in my 981 PDK Cayman S. The trip was 77 kms and the engine was warm.

I get about 6 mpg at the track. 🏎😀

Good work! I'm sure you have a lot of fun on the track. At the other extreme I used to race a 500 HP dedicated WRX track car running on E85 only. It had 4 x 1300 cc/min injectors that ran at about 84% duty cycle at full noise. 4 x 1.3 x 0.84 = 4.4 l/min - more than a US gallon (3.8 l) a minute. I never worked out what its fuel economy was on the track, but I would obviously need top up its 12 gallon tank for every session. Needless to say everything in the fuel supply system had to be upgraded and I needed to bring along a fair bit of fuel on a track day!

Wow, I thought I wasn't getting great mileage, but it seems I'm doing pretty well. I just had a trip to PA and back yesterday and today. On the way back today, I got about 25mpg and I was doing very silly speeds and having way too much fun. Normally, around town and normal usage, I get about 22mpg... Crossed 120k miles on the odometer during this trip... doesn't burn any oil either.

On a drive from Sydney, around Tasmania, and back I achieved 29 US mpg (8 l/100 km) at an overall average speed of 48 mph (77 km/h) over 2275 miles (3663 km) of varied city and country driving. Very happy with that. I've also seen mileage like @andrews

Is there a car ferry to Tasmania? I guess that I should have known!

I did an 8000 mile road trip in my 2007 Cayman S a few years ago. A mix of some spirited driving with a lot of interstate legs on cruise control. My average mileage for the entire trip was 25.6 mpg.

That sounds amazing...what was your trip route?? I would love to take mine on a road trip one time.

Very brief description- Start in North Carolina. Drive to Seattle. Visit son. Drive down the coast highway to LA. Head back to NC. If you search on "road trip" on my website, there are 3 in-depth articles. It was amazing www.newhillgarage.com I think it probably did a little better than 25 on the long interstate runs. The car is slippery aerodynamically, which certainly helps.

Not entirely sure what I was doing to get this mpg, neither hot nor cold (~70F), and probably doing 75mph on a 1300 mile road trip I’m assuming the taller 7th gear of the pdk helps some. On my regular commute to work, I’ll often see 30-31, though. And just after filling up, saw an optimistic range until refill: (iirc, it was at like 430 miles when I finally did gas up at the end of the run - definitely farther than usual)

It would be interesting to know how fuel usage is actually calculated. It has to be a little bit of a guess, as I am pretty sure there is no fuel flow meter on this (or any car). Indirectly, I could posit that the ECU does know specific fuel demand (the fuel map) at all times and could be making a running tally of demand versus time. That doesn't mean the car is using the fuel supplied in the most economic fashion. All of which is to say is how much faith can we put in any mpg value on the readout?

it’s a good question, particularly of how much can you trust the display number. Regarding how it calculates, given the primary job of the ecu is to meter fuel based on the wide variety of driving conditions and demands, plus the closed loop feedback of O2 sensors, id say it has a pretty good idea of how much it is putting out. Now how much that is doctored between the ECU and your eyeballs I couldn’t say, but I’m not sure why a sports car would need to be anything other than honest? My diesel gate era Audi tdi is definitely optimistic on the mpg readout, though, so hard to say for sure. I mostly just use it for qualitative diagnostics (eg. am I burning more fuel than usual on my typical commute loop?)

In a different ECU it calculated fuel usage by aggregating injector ‘open’ time. Injectors are only ‘open’ or ‘closed’. This might be reasonably accurate if the fuel rail pressure is constant or known by the ECU .

I believe the ECU calculates this based on on/off time of the injector, and knowing the flow rate of the injector and the fuel pressure - though the latter may be guessed as well. That said, it is a closed-loop system, so you'd think it should be accurate... but in reality, I have almost never had these readings ring true on any car... not just this one. I don't know why, but they have always over-estimated my mpg versus the fuel-tank method (miles driven computed with fuel gallons to fill). My Porsche usually does about 2mpg worse than the display... though sometimes it does get much closer... I wonder if that's affected by my WOT time versus tanks when I don't do it as often... never bothered to test that. Like Caylman, I really just use it as a "live" reference for how the car is running overall... I don't trust it for true reading of mpg.

If it is anything close to true, 34 is amazing. These days our 2.7 errand runner usually does shorter than 20 mile city trips with a cold start for each of those. The first 5 miles being 12mpg makes a lot of sense. Dash usually shows 15 to 21 with 8% larger than factory circumference rear rubber. Is the vehicle speed is taken from the front or rear?

If I remember correctly, I averaged 27-28 mpg on a 2,500-mile drive from Seattle to Monterey, CA and back a couple years ago. On a 150-mile weekend drive last week, the computer said 26 mpg. Maybe I don't drive my car as hard as some of you guys do? It does see redline several times on each drive, though.

As it should!

An interesting anecdote- This week, I took the 2007 Cayman on an 800 mile trek through the mountains of NC. Tail of the Dragon and Cherohala Skyway. Most of that mountain driving was in 2-3-4th gears. On the 3rd day, I left my accommodation and drove towards home at 60-70 mph in 6th. I noted when I left that the miles to empty was around 200. As I drove over the next 30 minutes, the miles to empty went UP, to a high point of 216. It was only an hour into the trip that it dropped back down to below 200. I am assuming it had "learned" my behavior of the mountain driving and applied that to the start of my 3rd day. Still, very strange.

Yes this is exactly what happened. The car does a rolling average of consumption based on the previous x number of miles, then applies that average to the amount left in the tank. When you get into 6th on the freeway, the consumption drops way down, so your expected range to empty will go up. Happens to me all the time. I drive around town (at probably 16-18 mpg), then hit the freeway and my range will continually go up as you saw. Perfectly normal.

When I drove from Long Island to the Traverse City Parade in my then 2005 Boxster S I was amazed to get 26-28 mpg even with doing 80 mph at times.