Tier1Terrier

What causes such dramatic reduction in fuel efficiency when car is in Sport or Sport Plus Mode (vs Normal Mode) if all other driving behaviors such as RPM & speed are the same? I have noticed that even on long drives at steady speeds in high gears that the fuel efficiency is greatly reduced. I have a 991.2 C2S in manual so assume that gear changes occur at the same RPM in any mode although in reality I tend to drive more spiritedly in Sport/Sport Plus modes.

Al.Fresco

I think part of it is that in Sport and Sport +, there is additional cooling, keeping the engine temps lower, which reduces fuel efficiency. But then again, I am an accountant and not an automotive engineer. ;-)

Rich_Jenkins

Hmm. What would you say is "greatly reduced"? Last time I ran a comparison was in fall of 2019. Driving to work in "normal" my average for three tanks was 23.5; five tanks with the rotary dial set to "sport" got me 21.9. I've driven the car in Sport mode pretty much all the time since. A recent road trip up to Tampa and back on I-75 for a dental visit I averaged a respectable 28.7, and I did not exactly leave the handbrake on.

asellus

A cooler engine is less efficient engine. Sport and Sport+ have a 15c or so lower target temp for the oil and facilitate this by routing the oil or coolant differently through/around the engine.

Sport+ keeps the turbos spooled a bit more. Sport does this by way of a less granular throttle pedal, so that can be mitigated by using cruise control or having a very light touch with your foot.

As mentioned above, air flaps up front are open more often (or always open) in sport/sport+.

Sport, with exhaust valves open, has the whole pops and bangs thing which uses some amount of fuel.

Idle is higher in sport and sport+ which is a not insignificant amount of fuel to idle the car compared to normal mode.

The increased load on the power steering pump for active suspension and engine mount stiffening in sport and sport+ can't be trivial, so that's more engine load.

There are anecdotal claims that the alternator doesn't disengage nearly as often as it does in normal when you're in sport/sport+, which would put a bit more overall load on the engine.

Rich_Jenkins

Good post.

Based on how much the "auto stop start" is touted to address fuel efficiency, I would hazard a guess you've identified the key difference between Normal and Sport. I pretty much reflexively turn the dial to Sport every time I start the car, and I've forgotten that there is a noticeable up tick in RPM at idle.

Fullyield

Sport and Sport + mode adjusts fuel/air mixture to run richer for maximum performance. Richer F/A mix also keeps engine at cooler temperature all else being equal. However, it also has less fuel efficiency and greater emissions. Lean F/A mix runs hotter and increases efficiency with less performance and emissions.

Schn3ll

A 911 is not a car you buy/drive to worry about MPG’s. I could care less if I got 5 mpg in mine. They offer Priuses for people that care about these things.

Just saying…

Edit: no offense intended, sorry - I guess I am feisty today.

Fullyield

I think everyone on here agrees with you. But, there are many reasons to monitor your fuel efficiency other than price of gas. I monitor mine just like all the other engine values and parameters. If my average MPG takes a drastic change then I suspect I have a possible vacuum or injector leak effecting the fuel air mixture. Owners of direct injected engines should be very sensitive to possible fuel dilution of the engine oil. A bad or leaking injector can thin your oil, wash down your cylinder walls and cause major engine damage if not caught and corrected.

chuckbdc

I'd bet biggest impact is that Sport and Sport + keeps the rpms higher that "normal" via the engine mappings, across all driving conditions from idle all the way through the gears.

XLR82XS

Couldn't. I'm a bit feisty today as well

good2go

My guess is the driver is just much heavier on the gas pedal in sport and sport+. At the race track I'm getting about 3 to 4 miles to the gallon.

Martin S.

Track mileage.....I just know in my 991.1 S/PDK I'll be on fumes after the third twenty (20) minute session of the day....I gas up at the end of the second session...

asellus

You actually make more power on a leaner burn, not a richer burn. More oxygen allows the fuel to combust much faster (to a point, this is nuanced).

I also sincerely doubt AFRs are meaningfully different at freeway speeds between the modes, but I haven't measured them. Maybe I'll go out and do that today, unless someone has measurements already handy?

Rich_Jenkins

The lowest I've ever recorded in daily use is 13.9. That was a fun afternoon.

To be honest though, I'm not too worried about MPG, as was stated. I do however appreciate the range of the car. A few cars back, I had an E92 M3 with a DINAN tune. The V8 was a hoot to drive, albeit a bit porky. But getting it going above 4,000 rpm, hoo boy. The thing was they put the same gas tank as the regular 3 series, so pretty much every time I looked up I'd need to get gas. If I recall it was typically 180-200 miles. Which was a bit of a pain in the rear.

On the 911, one of the many things that surprised me, coming from a '14 981S, was the overall usability of the car "as a car", including the mpg/range. I routinely see an estimated 400+ miles after a fill up. Using actual miles over actual gallons, since June 2019 my base C2 averages 24.3; not bad I think.

Valvefloat991

A few observations.

the water temperature is lowered in Sport mode, from about 220 in normal to about 185. Of course, the dumbed down water teperature gauge stays at 194 all the time. It's this reduction of water temperature that lowers the oil temperature, as the oil is cooled via an oil/water heat exchanger.

991s have electric power steering, so there is no power steering pump. Besides, the steering effort doesn't change with the drive modes.

They also don't have active suspension. PASM merely changes damping whihc is accomplished by adjusting valves in the shock absorbers. No incremental engine load.

Same goes for the adjustable engine mounts. Solenoid control.

The biggest change that affects fuel economy is in PDK cars due to a different shift schedule that holds the lower gears longer, generally running at higher rpm.