High Speed Fuel Economy

Shortly after installing my whipple I drove two hours or so on the interstate at 90+ and my on dash reading was around 23. My computer at that time would read around 2 mpg less than what I hand calculated.

I've since calibrated it and got it to read half a mpg lower than what it actually is, but I haven't messed with it for a while. Maybe this spring I'll get it spot on once I get the car out of hibernation.

If legit cruising, no stopping cause of traffic or whatever. Mid 20s is easy. The second you have to start using that skinny pedal is where you'll go down quick

I hit 27 on dash the other day coming home from San Marcos to San Antonio area. I've also filled up on west side of San Antonio and driven to San Marcos and dash read 24.7 I think and was creeping up still when I exited

Most of time though my trip mpg up there is much lower as I'm in stop and go traffic. I'm closer to 20-21 avg due to traffic

So basically, from what I can tell, if you fill up,.jump on interstate and cruise non stop for 3 hours, you ought to be mid 20s.

I cruise at about 80-85 on the highway and I get about 20mpg at that speed. I'm averaging 16-17 MPG combined.

I did a long trip last year and got 24.4 (hand calc) including some fun twisties thru the mountains.

The highest highway gas mileage I've recorded was at 80+ mph over 800 miles from Nebraska to Texas. Averaged like 25mpg, which is really good for the GT with 3.73 gears. Around town I get 14 or so.

On a ~280mi trip in Mexico travelling between 75-140+ the whole time with many WOT pulls I averaged about 14-15mpg.

On the same trip in Murrica staying between 75-90 with some WOT I usually can get about 17mpg.

18-20mpg in the rain, lol.

I'm heavily modded but my gas mileage actually wasnt much different stock. I averaged 19mpg and i usually cruise around 80 on the highway.

I take a 2.5 hour trip every couple of weeks. Cruise set at 80 the entire time and my 15 GT auto and 3.55 averages 22 almost every time. Calculated from the dash.

Just drove back from southern CALIFORNIA to OR so a 1k miles trip.
Had the cruise set for 84 mph most of the way with some very spirited acceleration to get around asses in the left lane. 22.1 mpg average
On the way down at mostly the speed limit, 24.3 mpg

3hr drive with the wife and kid while averaging 75-80mph, I hand calculated 22mpg. Including a few miles of stop and go city driving and the occasional WOT to pass truckers and slow people cruising in the fast lane...

I don't have a dog in the fight right now as I'm waiting on ours to be built. But, just a thought. If y'all could tell me what tranny, and what gears you have I can get a better read on the real world mpg's. Mine will be an A10 with the 3:15 gears. Thanks for your help.

Disclaimer: I'm not really worried to much about the mpgs as it is a Mustang GT afterall. But, just wondering.

wanted33 said:

I don't have a dog in the fight right now as I'm waiting on ours to be built. But, just a thought. If y'all could tell me what tranny, and what gears you have I can get a better read on the real world mpg's. Mine will be an A10 with the 3:15 gears. Thanks for your help.

Disclaimer: I'm not really worried to much about the mpgs as it is a Mustang GT afterall. But, just wondering.

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As I posted above my 15 GT premium is a 5.0, auto with 3.55 gears and it averages 22 mpg at 80 on longer trips.
You're right, after all its really about "smiles per gallon".

I could chime in since I just got back from a 1400 mile round trip. I was cruising 82 on cruise control most of the time. Sometimes 85-90 with a pack of speeders. I averaged 24mpg. I was refueling at about 325 miles and still had about 35-50 miles left per my gauge. The roads I took were I-10 from Arizona and I-5 to Northern California. Both roads have a good amount of climbing. The peaks were easily over 4000 feet. I am content with that mpg.

Oh...I have 3.31 gears and manual.

when i was stock cruising at 80mph i'd get ~24-25 MPG calculated through fuelly. 65mph cruise I got 27-28. 28.4 is I think the highest I ever recorded.

now that i'm supercharged, all highway 80mph cruise my average is around 22 MPG.

forgot to add, 3.55 gears and MT82

With 3.55 on my commute to work (129 miles), 75 on highway for 60 miles, 69 miles on secondary 60mph and a couple towns, I can get 29mpg for the trip.

If I set the cruse at 85mph I get 25-26 imperial mpg on shell v power 99 RON. At 70 I get 27-28mpg.
Both are over big distances so averaged out any inclines etc.