You are forgetting something: the transmission. Two things (well, more than two, as you can shift at pretty much any RPM) can happen if you put the pedal to the metal:
If you upshift at 1/2 of redline (or thereabouts, depends on the particular engine/transmission) you’ll get maximum efficiency.
If you upshift at redline (or thereabouts, depends on particular engine/transmission) you’ll get maximum acceleration.
To do either of these things in a car with a manual transmission is trivial. #2 in an automatic is trivial, too (just floor it). #1 in an automatic can be done by quickly lifting off the throttle. This forces an upshift. Apply the throttle again gently and stop at about 3/4 throttle to prevent a downshift. Again, the specifics depend on the particular engine/transmission.
My point was, and is, that instantanious mpg is meaningless. What matters is average mpg over the entire trip.
I took your assumption (slow steady acceleration gets the best fuel economy) and provided a counter-example with quicker acceleration and longer cruising time.
I used fuel per unit time because it was simple to show. If accelerating slowly takes 150 units of time to get to distance x, but accelerating quicker and cruising takes 100 units of time to get to the same distance x, you can factor out the “m” in mpg (because you are going the same distance) and just deal with the “g”. The lower “g” wins.
That’s where fuel per time unit comes in. In one case you are using a lot of fuel for the first 15 time units, but much less for the next 85. In the other case you are using marginally more fuel than you’d use cruising, but for 150 time units.
5cents, my point was that you haven’t shown any of those things. I’m not saying your conclusion is incorrect but the numbers you’ve thrown out aren’t enough for any conclusion let alone yours. I think you need to go back to physics 101 and relearn the relationship between distance, velocity and acceleration.
I was under the impression that these should not be trusted for instanteous measures. Is it possible that the act of accelerating throws off the measurement mechanism?
Depends on how the gauge works. In the '70s and '80s, these were typically vacuum gauges, and were horribly inaccurate, especially during acceleration. In the '90s, many of these gauges were fed by information from the FI system. Since the FI system knows how it timed the injectors, it can intuit how much fuel flowed through the injectors based on the characteristics of the injectors (its more complicated than it sounds, because injectors don’t open and close instantaneously), and it can determine distance travelled (speed or ABS sensors). In short, fuel injection based gauges are much more accurate, and aren’t as susceptable to wild variation when loads change.
No… those two dont go hand in hand. Vacuum changes rapidly, and is affected by throttle blade position and load. The higher the gear you’re in, the more load is on the car, not to mention the fact you’ve got extra wind resistance at higher speeds too. Its the same as trying to start off in 10th gear in a 10 speed bike… you have to push as hard as possible just to start. The load is higher. Vacuum gauges are still a good estimate for fuel mileage… the lower the vacuum the lower the gas mileage, thats just how it works. Its directly related to the fuel consumption of the engine… more load = more fuel. Simple as that.
…and considering automatic transmissions have torque converters… no, flooring the car until halfway up the tach is NOT going to do anything but waste gas… torque converters slip. They lock up usually around 45mph, or 3rd gear, whichever comes first. By going WOT from a stop you’re just unnecessarily heating the transmission and wasting energy as the torque converter slips. it’s also kind of retarded to save $200 annually in fuel costs while heavily accelerating the wear on $10000 worth of drivetrain parts. Definitely not worth it in the end.
Please note that I never said Mercedes was wrong. They provided emperical evidence from a single example. They did not provide any background data so we don’t know if that applies to every car under every condition.
What I have tried to say is that you provided small amounts of sometimes made up information and drew unwarranted conclusions from it. That doesn’t mean you are wrong but that you don’t have enough information to support your conclusion. In the first example you compare fast acceleration at 5mpg to slow at 30mpg. Do you know what the acceleration rates are in each case? Do you assume it to be proportional to fuel usage? Do you know what the cruise speed and fuel usage is?
You obviously have a lot of knowledge about cars. Not everyone knows that some fuel economy gauges used to be nothing more than vacuum gauges. I’m sure you also know that an engine may not get the same volumetric efficiency under full throttle and low vacuum than at part throttle and high vacuum.
I’m gaining nothing from this argument and do not wish the mods to ban me so feel free to have the last word.
Did you think I meant winding up the torque converter to 1/2 way up the tach? How silly! Just lift your foot off the brake and press it on the gas pedal. Lift foot when you get to 1/2 tach so the tranny shifts into second, then reapply gas pedal. Wash, rinse, repeat as necessary until you are up to speed.
But if you really think that lifting your foot off the brake and placing it on the gas pedal to WOT, then shifting at 1/2 tach really wastes gas, please tell Mercedes they are wrong. And if it blows up $10k tranmissions, please tell me who makes these wimpy, expensive transmissions, so I can avoid any car that has one. Even those funky (and crappy) ZF automatics used on some fancy European cars cost less than $2000, rebuilt. http://www.drivetrain.com/transautoimportapp.html