When you start accelerating from a full stop, what is your best method of acceleration to maximize FE, driving like granny (and get honked at once in a while), getting a little 'boost' or going hard on the throttle?

When accelerating slowly, FE is low. If you accelerate quickly, FE is even lower, but potentially for a much shorter period of time.

What do you do to maximize FE when starting from a full stop? Your comments are appreciated!

 

This topic has been debated much already. No conclusion has ever been agreed upon. Going way too slow so that you never hit top gear is clearly no good. Screeching squalling tires is also clearly not the best way. SOMEWHERE in the middle lies the answer. I tend to take off quicker than my fellow hypermilers. It is a trade off as you already mentioned, going faster does not use too much extra gas (not too fast) and it saves time so I go faster. The very best hypermilers go slowwwwww.

 

I have found this week that gentle but steady application of the throttle seems to yield a good result. I have 6 stop signs at the end of my run with lots of hills.

 

+1 for lakedude... I remember someone saying that the Insight did best with jackrabbit starts, so therefore the HCH must as well. I tried it for about half a week and watched my mpg drop faster than an H2 off a cliff. Lately, I've been operating on someone's theory that the throttle body is fully open by the time the engine reaches 2600rpm, and anything higher is just gratuitous. At that rpm, I usually see four or five bars of assist, while the impg hovers around 4 blocks (20mpg?). On this tank, I'm trying right foot cruise versus computer cruise, so it's hard to say whether or not my slightly higher average the past couple days is a result of the accelleration profile, or using my foot instead of the cruise, but I am up about 2mpg than average despite crap weather.

 

For those of you familiar with Honda recalling Sunbelt-area hybrids, a guy at the dealership recommened moderate use of the Asisst. Don't use a heavy foot on the accelerator - that was easy to figure out. He also said don't let the battery charge graph always max out either. That could be a bit controversial for hypermilers, but I've started to let the charge bar go a little lower....

 

Since I started using the hypermiling techniques I have found that an aggressive start gives me the best FE. What I do from a stop is wait a little to give myself some room and then depress the accelerator enough to get at least 50% Assist and then build up speed quickly to a few mph over the speed limit. I then back off the accelerator to coast down to the speed limit. By now, I'm at the speed I want to be at and my FE gage is between 70 and 80. I feel this method get the most out of the IMA as that's what it is there for. My first two tanks without hypermiling techniques averaged 47.3 mpg. The third tank using the techniques was 52.6 mpg. I'm now on my fourth tank and it looks to be around 53 mpg.

Mark

 

Meggert, sounds like we may be ending up with just about the same result, but getting there through different methods. Next time you're using your 50% assist technique, take a look at where your rpm is. I have a feeling it's probably in the 2500-3000 range.

 

I find that an acceleration between 1500 & 2000 RPMs with 3 or 4 bars assist works best
for me. The occasional situation occurs where I need to bring it over 2000 but not
to often, really brings the tanks avg. down.

 

Short answer: It depends on the car. Trial and error testing is your best tool.

Long answer.

The best average fuel efficiency will come from optimizing the applied engine torque (as measured at the wheels) verses fuel consumed throughout the velocity change curve (holy technical talk, Batman, doesn't that sound intellectual!). In other words, for any given car it will generally depend on the engine RPM/torque curve coupled with the transmission gearing vs. actual fuel consumed.

The idea is to spend as little time in the lower gears as possible without lugging the engine (everyone know what the phrase "lugging the engine" means, right?), and then once the engine shifts to the highest gear, ease off the gas and gradually gain speed after that point. A rule of thumb is that most engines develop their best torque efficiency around the lower third to half range of the rated RPM. So, most typical ICE powered cars should get their best gas mileage through the lower gears somewhere between 1,500 to 2,500 RPM. If you are accelerating hard enough so that the engine revs past 2,500 RPM in this hypothetical example then you are probably not getting the best mileage.

In my case, it seems I realize the best gas mileage while accelerating between 1,000 and 1,700 RPM (this is not a hybrid car BTW). So, I accelerate modestly and ease off the gas once the engine RPM gets to 1,700. After the transmission shifts, I get back on the gas -- not enough to make the transmission shift down a gear -- until I get back up to about 1,700. And so on and so on. After the final shift into high gear (which happens at about 35 MPH), I poke along gradually gaining speed until I am up to my goal.

Of course, all other things being equal acceleration to a given speed is a trade off with time. You will always get better mileage once you are in high gear if you accelerate slowly and practice long and slow speed changes while in high gear.

Now, if you have one of these new fangled constant velocity transmissions then same considerations apply, you just have to know the RPM torque curve of your engine vs. fuel consumption and adjust your acceleration to maintain an appropriate engine RPM.

 

I am still on my first tank of gas and I have been accelerating gently for the most part and am maintaining very high FE. I think I will try a little more agressive approach on my next tank and see if the numbers change. I generaly limit the boost two three bars (as someone had recommended) and it seems to work well.

I have limited experience with our Prius as my wife drives it most of the time, but I find if I accelerate so that the car's engine is only powering the drive wheels and not recharging the battery, I get the highest FE, and it is more of a moderate than gentle drive, and does change as speed increases.

Thanks for all your tips. I will, over time, try them all and see what works best.

Isnt' the HCH2 just a super fun car to drive? I had to drive my old car today - used to think it was the best, but not anymore!