After having this AT for a year, I have a theory now.

The AT programing tells the tranny to choose the highest gear possible when driving, so it upshifts often. This puts the engine below it's powerband and below it's peak torque range.

In city driving, you are constantly increasing and decreasing speed. Once it upshifts, you must tip the throttle a certain percentage in before the tranny kicks down to a lower gear. During that lag time, you are having to dump the gas to it to get any meaningfull accelleration.

So you are out of the powerband for most of the time you're driving.

With a MT, you control where you are in the rev range and thus you can stay in the powerband. The engine is performing much more efficiently.

I would further postulate that with an AT if you go into Sport mode and manual shift with the paddles, you could also control the powerband much better in stop and go city traffic, and get better mileage.

I am going to try driving for an entire tank in manual mode and see how it does.

 

I've been wondering that myself.... next tank maybe I'll try it myself.
(I'm usually in "s" mode on the interstate but put in in "D" between traffic lights & just manually shift as needed.... might make a 3-5mpg difference.

 

there's no reason why the AT would get better mileage. the AT has more drag. even on the freeway, the AT fit would have to work harder to go the same as a MT fit. therefore using more mileage. it isn't about the RPM your car is at. it's the throttle position

 

I am not talking about the AT getting better mileage than the MT. I am talking about how can we get better city mileage from the AT period.

Imitating the MT by using the paddles should increase the AT city MPG, but I doubt it would be better than the MT, no matter how you shifted.

And why is there more drag? The AT and the MT are the same aerodynamically, right?

True the AT has more parasitic loss because of the torque converter, thus less power gets to the ground.

And where you are in the powerband, will directly affect how much throttle you have to use, for a given rate of accelleration. So they are both important.

 

While the title may be misleading.....Sid, I read your thread to be about improving AT mileage to be more like the MT.

 

I read it as he's trying to get better mpg's out of his AT fit not get better mpg's than an MT.

I really think that you may be onto something and you'll most likely find what you're looking for.

 

Maybe the correct title should be:

"AT City MPG : 'D' vs 'S' with Paddle Shift, Which is Better?"

What I am comparing is drving an AT as an AT in regular "D" mode or trying to emulate a MT and use "S" and the paddles. And I think using the paddles will give you better city MPG than using "D".

The reason the MT is better at city MPG is because you get to choose the gear you want to be in when you upshift AND downshift, thus maximizing the engine's inherent powerband.

 

I believe that "s" mode def. help to keep the rpm's \/..... therefore decreasing amount of fuel burned... I think that even driving in "D" conservatively doesn't keep the revs down as well as I can manually.
The question is how much dif. will it make?

 

reps for everyone!!!

 

Don't forget that your Torque Converter is maybe the largest eco loss item. It's always slipping unless locked up when at steady cruse speed and locked up. For sure when in OD but I'd guess also in high gear. That slippage generates heat and wasted fuel.

Of course this is in addition to the NON-Eco shift programing.

I have not seen any data yet, but my guess is if you put two Fit's side by side, one with MT and one with AT and just cruised for 50 miles at 66mph on flat ground stead throttle, the AT would do better because of the lower eng rev's per mile. Anyone else see that or not?

 

I would agree... given the exact same highway speed, the AT should probably get better economy due to lower revs.

AT losses are going to be felt more during average driving. Again, since the AT takes power from the engine to perform it's shifts, where as a manual takes power from the driver to shift.

 

I think you theory will prove to be partially correct, but the variable you are missing is the clutch. When you let off the gas in a AT car the car slows at a constant but slow rate. Your RPM's drop, but most drivers will not have a long gap between gas and break. Usually it is a much shorter period of coasting for the main reason of ride comfort. In a MT car you have the option of pushing in the clutch to coast. You will still slow down, but over a much greater distance than in a AT car -AND- i find there are a lot more MT drivers that will have no problem coasting longer distances than in AT cars because you are bale to control the time/rpm/speed that the clutch is engaged. If done properly a MT can be as comfy if not more so than a AT. I know i can make my MT car shift smoother than my gf's AT car (not to say i do.....but i have the option).

Finally there is the 'other' addition of a MT regarding the clutch: Full Stops. When at a full stop you have the option of keeping the clutch pushed in or shifting to neutral and letting the clutch out - either of which will take almost ALL of the weight/load off of the engine, lowering the rotational weight/force, and lowering the overall use of fuel. In a AT car you do not really have that option. If you take your food off the break your car begins to move forward proving that there is still a load on the drivetrain. That load causes the car to burn more gas whenever stopped or stopping because it is always there.


I think i have said enough for one post. MT sill remain the winner, but AT may be able to increase MPG by a couple miles if driven 'properly'


Good Thread!

 

Cavie, your first point... at least I think you were trying to get to, was probably thinking that coasting gives you better fuel economy. Is that correct?

Thinking you get better economy by coasting in neutral as opposed to being in gear is not correct. It's been found (mentioned in the ScanGauge thread) that letting off the throttle while in gear cuts fuel to the engine - in both MT and AT models. Shifting to neutral forces the engine to idle, which uses fuel. Not using fuel is more efficient than using fuel in every situation!

Your second point is correct. Being in neutral at a stop is more efficient, since there is no load on the engine. In the AT cars, the torque converter is still connected to the engine, and does incur a small amount of load.

Sometimes at lights, if I know them to be more than a minute or two, I'll shift my AT to N.

 

That i did not know. I stand corrected -somewhat-.

Why would your fuel cut when letting off in a MT car? Would it not return to idle? in a AT car the torque converter completely disengages (as in 100%) when you let off the gas?

...something does not make sense here. Not saying you are wrong, just trying to understand.


I would imagine .....

 

The only thing I can say about the Torque Converter is when you hit 4th gear at 35 mpg, pay attention to your throttle very carefully. If you push too hard, the RPM meter will read 3K. But if you lightly coast accelerating only .5 mph/s, you'll see that you're actually acelerating with RPM at 2K. The same goes with 3rd. After you hit 20 mph on 3rd, hold your RPM on 2.5K, you'll see something interesting. The speedometer will go up, but the the RPM reading will stay the same. But if you slam on the gas, the RPM meter will jump over 3K. Right now, I'm assuming that VTEC is causing the 3K surge. Not completely sure if it's VTEC or the computer since automatics are suppose to be design in a way that the engine never stalls. So I guess maybe it's trying to protect the engine by surging or downshifting? Hurray for Drive-by-Throttle... lol... actually it's not that bad after I got used to it.

 

I don't think your theory will pan out because the best mileage is obtained when conserving energy as much as possible and this requires coasting as much as possible. I'm not talking about coasting in neutral, but rather accelerating gently, calculating your next stop, and getting of the gas as soon as possible so that you can coast up to the stop sign, traffic signal, etc.

The Fit will coast in this manner a lot farther in 4th gear than in 3rd, which is what you're going to be in a lot in "S" mode. If you take your foot off the gas in 3rd, the car will lose speed rapidly and not coast nearly as far as in 4th or 5th.

Staying in the powerband by using the paddles will have a negligible benefit as compared to using "D" and conserving your energy by accelerating gently and planning ahead.

I've experimented with lots of different techniques with my A/T, and the best mileage in city driving is to leave it in "D", accelerate gently, and get off the gas when you have enough momentum to coast to the next stop.

Of course, that's no fun at all, so I mostly use my paddles and drive the hell out of my Fit.

ez

 

edit:

I misread