Originally Posted By: Quattro Pete
I've got a manual. The mpg I listed is with cruise control set at around 70 mph on an interstate hwy, running Shell 93, GC, RP Synchromax in the tranny, and Redline in the diff. Same factory sport suspension and OEM 17x8 rims with Bridgestone RE960 235/45/17 tires.
Considering EPA rates your car at 26 mpg hwy, you're beating it by quite a bit. Just to make sure, we're talking about US gallons, not imperials ones, right?
Perfectly valid point, made that mistake before....
At 70mph, I would probably be getting the same as you, and I would expect your M54 to be superior to my M52. As I mentioned I find my engine/gearing best in the 80-100kph zone. In these conditions I absolutely recall getting 6.5L/100km or 6.6 several times, which onlineconversion.com states to be just over 36mpg(US). I believe I also managed 6.3 once, that's mid 37 mpg(US). I acknowledge that was up in my "best ever" territory but it was not with a 100kph tailwind coasting downhill or anything like that.
The "40" must have been a UK conversion stuck in my head from a while back, I throw myself at the mercy of the thread.
If I can't achieve 7.5, something is wrong (bad gas, strong headwind, dragging a piano) and that exceeds 31mpg(US). On an interstate (>70mph) I'd consider 7.0-7.5 typical, so 31-33+.
The stretch that generally gets used for mental reference is a vacationing run from one Great Lake to another (Ontario to Huron) on a route that's straight with few stops and not a lot of passing required, but there are hills. I generally do more observing of fuel economy on the way there (west) with prevailing head winds.
In day-to-day use, I'm not driving for fuel economy so I'm usually getting 20-24 almost all city.
My whole on-topic point about GC was that with this engine I feel good about what I'm achieving which, I'll happily rephrase, "well into the 30s" when I want to. Winter gas is another story