Quote:
Originally Posted by Chance
Fuel economy comes from reducing BSFC (brake specific fuel consumption) which is not necessarily at lowest RPMs and or higher torque. There’s such a thing as overdoing it.
Ideally you’d size engine so it operates most of the time in the bulls eye area of BSFC map. The problem is that if you do that (which often leads to smaller engines), the transmission will need to downshift when extra load is placed on engine; as when accelerating or going up a hill. An occasional downshift doesn’t bother me, but is does most drivers.
I think a major reason for new 10-speed auto transmissions is to make shift increments smaller so they are not as noticeable and thus annoying to drivers.
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My GMC Terrain has a turbocharged 4 cylinder (start/stop) engine and a 9 speed transmission. The transmission is a marvel of smooth shifting technology and is always in just the right gear. But it’s really vexing to drive. To go up just about any hill there is a noticeable turbo lag and a downshift of two or three gears. It’s a very busy drivetrain. I expect most drivers would quickly get used to it and I did too - until I get in my “old fashioned” Jeep with its straight six and a four speed transmission. SO much nicer to drive. Of course, the gas mileage is at least a third less, but I like the trade off!
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