Most fuel efficient speed (highest MPG)?

So many people focus soley on the speed....

You need to work on anticipating stops and letting off the gas pedal and gliding for as long as you possibly can. Do this on country roads and you will see a big jump in milage. I also do this on residential streets. There are MANY cases where you can accelerate from a stop sign and just lift the gas, reapply a bit of pressure and glide to the next one. Most people just accelerate up to speed then sit there with their foot on the pedal and the ICE running then start applying the brake for the next stop. This is very inefficient.

I used to never get over 50mpg but once I started playing around with gliding to stops from as far away as possible my milage shot up and getting 51-53mpg was realitvely easy. I would need to P&G to get over 55mpg though.

All that changed when I swapped to new tires and changed my commute which now inclused a 2,000 elevation gain every day.

 

I didn't know that the ability to P&G is limited at low speed, and also overcome by reaching higher speeds. Is this limitation only observed when not in Stage 4?

 

IF you are not getting into stage 4 if you have not hit 157F and you do the idle check stop. If you are not in stage 4, then the ICE will not turn off below 34MPG.

Yes I have and EV switch and and EBH and I use the EV switch to kill the engine in stages 2-3. This helps tremendously. The EBH lets me start with 125-135F at startup.

I am not using the temperature sensor hack. If you use the EBH, since I start with such a high temp, I get into stage 4 very quickly.

 

I take that back i found your other thread, my question though is where you got the 190 from.

 

I still P&G when I can, often i forget though and just drive it. Came in from St.George last weekend and was going 85 on the freeway, I still netted around 43mpg. It's creeping back up towards 46 avg now with P&G and gliding. I still managed to get 479 miles on that tank with aggressive driving. I attribute some of that to the fact I used Shell gas on that tank, my mpg always shoots up easily when using Shell gas. The prius loves it, the new Nitrogen enriched stuff seems even better.

driving 50 in a 65 is dangerous around here, likewise going 25 in a 45 is really bad, and will probably get you a ticket. The only time I P& G are on side routes, off the main drags.

 

if anything shouldnt the Nitrogen decrease gas milage b/c the gas then has a lower % of gas in it and thus a lower energy content?

 

Ken@Japan found it in a Japanese web site. This is the rolling drag used for the NHW11 Prius, the model I drive.

Folks have been using one of two formulas to express the vehicle performance:

• Drag_force = rolling_drag + (Cd*A*p*(v**)) ## traditional
• Drag_force = C + (B*v) + A*(v*v) ## EPA approach

rolling_drag - treated as a constant
Cd - coefficient of drag for vehicle
A - cross-section area of vehicle
p - air density
v - velocity

C - fixed drag force
B - drag force proportional to velocity
A - drag force proportional to velocity squared​

Bob Wilson

 

For all we know it's more energetic than gasoline, but in any case it's a trivial amount of material and will have no significant direct effect on MPGs. Even E10 is only 3% less energetic than gasoline, gallon for gallon.

 

interesting b/c I have my own version of your spreadsheet I made some time ago and I use 144 N for the rolling drag

F = mg*mu

m = mass = 1398 kg
g = accel of grav = 9.81 m/s^2
mu = coefficient of friction = 0.0105

I forget where I found the 0.0105 but is the difference in the equation.

 

I can believe it is lower for the NHW20 due to the lower transaxle drag. Pump the tires to max PSI and you're there.

Bob Wilson

 

That's all good, but do you know how to consciously stop the gas engine (ICE) , at will, and attain a glide below 41 MPH, or warp stealth above that speed? If you don't do that, or are not aware that you can, you won't get the stellar mileage that you read about here.
Turn you A/C back on. set it for about 76-78. Running the A/C has little impact on MPG, infact you need to run it when it's hot, to keep the battery cool, which will result in better MPG by allowing you to better glide and warp stealth. If you are feeling hot, so is the battery.
What do you inflate you tires to? I'd suggest 42/40 psi as a minimum if striving for great gas mileage.
I leave my A/C at 78 deg. and never get hot. I regularly get 60 MPG and over 600 miles to a tank.

 

Hi Bob,

That "EPA Approach" is just a polynomial expansion. Its common for experimentalists to use a polynomial expansion to describe a measured curve, rather than an theory based equation, that is incomplete (such as the what you call "traditional") and thus does not match the measured curve exactly.


Hi Best....,

Well, when I was using the MYCANSCAN, I saw failures to auto-stop with the car as hot as 90 C (194 F) and with speeds greater than 35 mph. So, the car is well into stage 4, had been for 10 minutes or more, and still would fail to auto stop. The 70 C (158 F) limit just gets you into to a point where it will auto stop if you go for a glide above 35 mph. It still has a whole bunch of warm-up tricks to do before it locks in the auto-stop during with a 35 mph speed, let along at low speeds. Possibly your not noticing this because your driving in an area where the car rapidly transistions from 70 to 90 C . In suburban traffic, its common to have the car up and down between those two numbers before it will finally stays up at 90 C. When the car gets above 73 C, it will stop auto-stoping (at speeds greater than 35 mph). Then it will start back up when it gets above 76C. Additionally, I forget the actual temp, but somewhere in the mid-80s, the temp will do a little drop , and during that time (presumably when the thermos is being filled with hot coolant), the car will not auto-stop at speeds above 35 mph. This comfounded my mileage on one route, because that happened just where there was a nice shallow 2 mile long glide road. Everytime you glide its down below that 80 something temp, and then back up near that 80 something temp, and the car is going to no-auto-stop mode. They need to make that action more asyncronous, such that it happens once, and is done with it. The effects there are dramatic - if auto-stop is working 100 mpg plus for that section, if not, 60 mpg.

That last paragraph is all about the 35 mph plus autostoping. Sub 35 mph autostoping is not even noticed till the car has been running about twice as long.

SO, now I am more than 1/3 the way through my commute and the car is now reliable at auto-stopping above 35 mph, and the temp is 88 C or above. But lately, due to a deviation to avoid construction, there is a long shallow 30 mph glide I am doing, and after that there is a hill. With the normal route on this hill the car reliabley autostops above 35 mph. Not with the new route and the 1 mile 30 mph glide (after peaking at 35 mph briefly) just before it, even after climbing the 35-40 mph hill. Without the Mycanscan I cannot tell you temps, and also without it I am not risking more grill blocking than 1/3 on the bottom and full on the top. This happens with temps in the mid 70's F. I have never been able to correlate these actions to cat temps on the Mycanscan, but I did not know what to look for. The temps get above 400 C rather quickly and stay up in the 500's C most of the time.

Its this issue that prevents me from getting over 70 mpg on a tank. Somedays it will be flawless, others it will not develop the no-auto-stop syndrome.

I have no modifcations to my car other than some aero-mods, and the above mentioned grill blocks.

I am loathe to try the thermistor hack, without some sort or more smarts in the modifications. Something like a PIC controller, which would present the true temps to the ECU, after a certain temperature is reached (90 C?). I am also loathe to use a scan-gauge due to poor operational ergonomics of this legal device. The MYCANSCAN resolves the operational egonomics of an almost full (does not have injector pulse width) featured dash board. But, its illegal here in Illinois as its implemented on a PC platform. If it was a stand-alone, even with the same 7" diagonal screen, single purposed device, it would be legal. Without the temp gauge, I cannot run more sumertime grill blocking. From when I was running with the temp gauge, I could tell that for my routes, a good grill block in temps above 60 F at the beginning of the trip, was too much at the end (to the point where autostop was not occuring, as the engine wanted to run the water pump to stay cool). A variable grill block is really needed.

BTW, finished this latest tank at 66.6 mpg.