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Normal driving which is 60% city-ish 40% freeway I get in the 17-18 mpg range. I did do a 4am run to San Diego and back (i.e. 80 mph, no traffic) and did get 23.4 mpg.
Fuel mileage tends to go down when you drive on winter blend gas (which we have in the NE now), and it gets worse if it is winter blend in warmish weather (as it has been).
Bruce is probably running on 93 octane, as that is pretty much the default premium octane in Philly.
Average speed hides important stop/go data. You could do stop/go and raise your average speed by doing 80. The average looks like a tidy 65, but details affecting MPG are lost.
I don't shift in 6th until something like 70 -- wonder what Bruce does.
Ever since buying my 911SC, I've always recorded miles and gallons used. While I had my 2002 996 Carrera(bought used at 77,900 miles, IMS failure at 100,480), I filled it up 75 times and calculated the relationship between the computer indicated mileage and my calculated mileage (miles since last fill up ÷ gallons to fill up the tank). The graph shows the results. The purple filled diamonds are from a 5500 mile road trip with very little stop and go traffic. The grey line is a 1:1 slope as if the computer was identical to actual results. The blue line is the fit to the data.
The actual fit was Y (computer indicated mileage) = {0.994 ± 0.046} X (actual mileage) - {0.48 ± 1.16}
Overall, this shows that, on average, the computer is quite accurate. However, at any given time, it can vary by 3/4 of a MPG.
Having bought my 997.2 two months ago, I don't have enough data (only 4 tanks used so far) to make a comparison, but will continue to record how much gas I use.
You are somewhat reliant on the computer values as many metrics are not practical to measure precisely.
Gallons of fuel added - depends on the precision of the pumps used vs via a reference volume container & variance from station to station.
Miles driven - depends on accuracy of the computer vs actual miles (actual wheel diameters, slippage, etc)
Ever since buying my 911SC, I've always recorded miles and gallons used. While I had my 2002 996 Carrera(bought used at 77,900 miles, IMS failure at 100,480), I filled it up 75 times and calculated the relationship between the computer indicated mileage and my calculated mileage (miles since last fill up ÷ gallons to fill up the tank). The graph shows the results. The purple filled diamonds are from a 5500 mile road trip with very little stop and go traffic. The grey line is a 1:1 slope as if the computer was identical to actual results. The blue line is the fit to the data.
The actual fit was Y (computer indicated mileage) = {0.994 ± 0.046} X (actual mileage) - {0.48 ± 1.16}
Overall, this shows that, on average, the computer is quite accurate. However, at any given time, it can vary by 3/4 of a MPG.
Having bought my 997.2 two months ago, I don't have enough data (only 4 tanks used so far) to make a comparison, but will continue to record how much gas I use.
You sir, are a nut. I salute you!
All gas I used was 93 except my first fill in Philly at a WaWa at 92.
The fills with the higher avg mph were almost pure highway and conversely city.... The avg mph appears to accurately reflect the mix of highway vs local iirc.
My driving style is a bit on the power side as I like higher revs... Not to red line, but I think I run them up more than most. On the highways, I almost always shift to 5th on inclines and when I come into congestion, even at higher speeds, I shift to 4th just in case to hit a gap or get out of there..... I definitely don't just drive in 6th all day on the highway as I am an active shifter and like to have power on hand. Once relaxed, I am in 6th. Oh, and i always rev match my downshifts...fun. Fwiw.
Peace,
Bruce in Philly
Last edited by Bruce In Philly; 12-22-2015 at 07:59 PM.
All gas I used was 93 except my first fill in Philly at a WaWa at 92.
The fills with the higher avg mph were almost pure highway and conversely city.... The avg mph appears to accurately reflect the mix of highway vs local iirc.
My driving style is a bit on the power side as I like higher revs... Not to red line, but I think I run them up more than most. On the highways, I almost always shift to 5th on inclines and when I come into congestion, even at higher speeds, I shift to 4th just in case to hit a gap or get out of there..... I definitely don't just drive in 6th all day on the highway as I am an active shifter and like to have power on hand. Once relaxed, I am in 6th. Oh, and i always rev match my downshifts...fun. Fwiw.
Peace, Bruce in Philly
That's certainly what my wife has said about my cars.
In CA, the typical high octane is 91.
Driving style is primarily hyper-miling, but I don't do the Speedo-indicated upshift until I get to at least 2000 rpm (primarily because most of my driving is on dull/boring roads).
Can I ask, do you often reset the mpg function on the on-board computer? I feel like I do this frequently, and often it seems much higher, but does not really back down to a lower level during longer trips? I really feel the mpg is more like 16-18, when the computer is logging 21-23+
I can actually see the gas gauge plummeting during my driving, with mpg readout holding steady. also driving on 91 octane.
Can I ask, do you often reset the mpg function on the on-board computer? I feel like I do this frequently, and often it seems much higher, but does not really back down to a lower level during longer trips? I really feel the mpg is more like 16-18, when the computer is logging 21-23+
I can actually see the gas gauge plummeting during my driving, with mpg readout holding steady. also driving on 91 octane.
Would adding in fuel additive change things?
I reset it when I think about it. In traffic, and when I am bored out of my gourd, I reset it and play games such as trying to get it as high as I can such as coasting down hills.
IIRC, it is really wrong immediately after you reset it, but falls in line after a few minutes. I often wondered about the algorithm in there (maybe I should think of women more), such as when does it stop tracking when you stop moving....... sitting a traffic light, you burn gas but don't move. It seems to disregard long stops.
To understand the impact on mileage from octane and additives, you really need to take down some serious notes and do it consistently for a long long time and then run some statistical analysis on the data.. I am a geek but not a totally committed one.
In our '07 GT3 I figure the faster I go the quicker I get to my destinatation so my engine is not running as long, hence I use less gas to get there! Makes sense to me
In our '07 GT3 I figure the faster I go the quicker I get to my destinatation so my engine is not running as long, hence I use less gas to get there! Makes sense to me
All the best...
Good point. It also lowers your chances of a traffic ticket.
It would be interesting to dig into what the MPG calculation of the On Board Computer (OBC) and what goes into it.
In the purely accurate area, it can accumulate gas usage via the injector data, and mileage from the wheel data (or GPS) to compute MPG. So standing still does consume more gas while not adding any more miles so, it presumably just has two running additions of gallons consumed and miles driven, and the OBC display in the cluster is just the result of a division. (and a multiplication if it needs to also convert units).
If its trying to be different, it could try and tell you what your MPG is while in motion, because you don't have much control over when you stop and for how long typically, but you do have control on braking, accelerating and the like along the way, so this would be better at informing you on a more efficient driving style. But its a 997, so who really cares about that?!
I've also played the games of resetting as I'm driving down a hill, and the injectors are occasional shut down by the engine system as momentum is enough to keep speed, to see the MPG climb into the crazy high figures... (all miles very little fuel consumed rolling down hill)
12-22-2015, 01:38 PM
at 100,480), I filled it up 75 times and calculated the relationship between the computer indicated mileage and my calculated mileage (miles since last fill up ÷ gallons to fill up the tank). The graph shows the results. The purple filled diamonds are from a 5500 mile road trip with very little stop and go traffic. The grey line is a 1:1 slope as if the computer was identical to actual results. The blue line is the fit to the data.
