chrisp@oliven.UUCP (Chris Prael) (06/17/84)
Your friend was talking about power/torque effeciency, NOT fuel efficiency. The only company to do any study of fuel effeciency under acceleration is BMW. Their lint of "eta" engines is based on their study. They published the results two or three years ago. BMW's basic findings were that the most fuel efficient acceleration occured with full throttle at the lowest possible engine speeds. Their general recommendation was to use full throttle and shift at 2000 rpm. Their deductions from the tests were that intake system flow was most efficient at full throttle. Next, although the engine produces more power at higher engine speeds, some of this is at the cost of increasing friction effects within the engine. So, the lower the engine speed, the less power loss due to friction. I tried their recommendations as nearly as my '70 Alfa would permit for a few months. (The Alfa will not function at all, at engine speeds below 2000 rpm, so I used 3000 rpm as my shift point, instead of my usual 4500 rpm to 5500 rpm.) I found that in surface street operation, that the method was worth 1/2 to 1 mile per gallon improvement in fuel milage. This amounts to an improvement of 2.5% to 5%. Not worth the trouble and agrivation in my view because it is hard to do this smoothly enough for my taste. Your friend's recommendations about "keeping the revs up" provide more efficient operation from the standpoint of control of the car. At higher revs you have more power available when you need it, hence you enhance your control of the car and have more options available to you in an emergency situation. Your basic choice in this is between safety and economy. Since you say that you cruise at 55 mph, I would assume that economy is more important to you than safety. Chris Prael