After fitting new Iridium plugs, cleaning injectors, replacing fuel filter and using only 94 RON premium, have been measuring fuel consumption on my '05 STR for a few months. Around town, with about 20% highway driving, am averaging 21.0 mpg (17.5 m/USG).

A few days ago went on a 400 km cross-mountain road trip with no A/C, got 27.3 mpg (22.7 m/USG).

Then return journey of 400 km with 91 RON premium and A/C all the way, got 24.1 mpg (20.1 m/USG).

Of that 3.2 mpg reduction, what do you think would be the split between the 91 premium and the A/C?

 

I'd be guessing 3 for 91 and 0.2 for a/c, if it's reasonably well charged. I'm working on the basis that your car is not calibrated for 91 (mine's minimum is 95 RON).

 

I've been getting between 22.8 mpg and 23.8 mpg on my 320 mile each way weekend commute. (Basically flat roads, on cruise control a few miles above either the 70 or 75 mph speed limits, 92 octane gas.)

But! When I watch my instantaneous mileage and increase my engine rpm about 1000 rpm on cruise control, (speed limit + another 1000 rpm), my gas mileage actually goes up about 2 mpg. I figure I am driving at a more efficient speed/engine rpm for the super charger.

 

Sorry, didn't mean RON when describing premium. The 94 premium in Canada is maybe 97 RON, and the 91 premium is maybe 94 RON.

 

Thats good info, thanks for sharing your awesome MPG.

I recently got 24.5 on a 300 mile trip where I gained 4000+ft in elevation, and of course lost it on the way back with some very uneven terrain in between. The ignorant drivers that cant use cruise control didn't help either. One thing I noticed is that the car didn't necessarily gain MPG when I was gliding down 3000 ft over a 40 mile period which I found interesting. Granted this was all with the AC on in 100+ degree weather and 175 lb's in extra weight on AZ 91 oct. I was hoping to get 26 mpg, but soon go over when I did a 3rd gear 60mph to 90mph pass in third gear, and confirmed my suspicion that this car is a beast on the freeway.