We were alerted by Jim Park, our colleague on the Canadian HighwayStar Magazine that he had not achieved very good fuel mileage on his test drive. But he had taken the truck before the roof fairing had been fitted. With that fairing, plus some additional schooling in the optimum technique for driving the ACERT Cats, I did better. When we checked the fuel mileage we were astounded to find we had bettered Jim by 2 mpg, returning an overall of 6.88 mpg for our 346-mile round trip.
The trend seems to be on the new trucks that the RPMs have to be kept in a tight low range. Detroit wants 12-1500 for theirs. I don't know yet where the '07 engines are going to go on Drivability. MPG might have been boosted slightly by going to a direct setup (1:1 top gear and rear end ratio in the 2.6-2.9 range rather than the more traditional .7 top gear and 3.55 rears) and also wide base singles and extra trailer streamlining could make a small improvement. I hope Cat can move forward in MPG in '07 like Detroit and Cummins have indicated they will.
The 386 might be a decent compromise for fleets wanting to be able to convert the tractor to a daycab later on. The 379 is a nice piece of work (they've been building it for years so all the bugs are worked out) and is very popular with drivers. Being a traditional simple design the parts are cheap and easy to obtain (Windshield for Pete 379 is about $40, windshield for the Ultra Aero 387 is near $700 and requires the truck be Out of Service for 24 hours.)