The difference between nice-on and fas

[bomber991]

Alright, so all I've been doing for a while is nice-on coasting with my p&g routine. I've been able to maintain about 30mpg with the city type driving I've been doing. I think I might start throwing fasing into my routine.

So what I want to do in this thread is show the potential difference between nice-on coasting and fasing.

Ok, so I'm not quite sure how many GPH i'm using while accelerating. I do know that when I go from 50 to 60mph I'm doing about 14 to 15mpg. But with mostly city driving my accelerating seems to be done from 30 to 50mph so the mpg range is lower. I've noticed it doesn't seem to go under 10mpg while accelerating, I think 12mpg is the highest I get it but I haven't watched close enough to tell.

So for the calculations I'm going to do, I'm just going to assume I get 13mpg while accelerating, since this will have less fuel used during accelerating, my numbers should be an underestimate of what I can achieve.

Alright, so lets say I accelerate for a distance of 1 unit at 13mpg. To determine the fuel used we do 1 unit divided by 13mpg. Comes out to 0.0769 gallons of fuel to travel 1 unit.

If we want to get 30mpg, which is what I've been getting with nice-on coasting, then we must have distance/fuel=30mpg. So (fuel)X(efficiency)=distance. In this case, (0.0769)(30)=2.307 units of distance.

So 1 unit is consuming fuel at a rate of 13mpg, and 1.307 units are consuming no fuel since this is a fas, but what if this was a nice-on coast?

My car consumes 0.3gph at idle. So at 40mph in neutral, I get (40/0.3) 133mpg instantaneously and at 30mph I get 100mpg. Most of my coasting seems to be around 40mph, and since 40mph also uses a little less fuel, we'll use that for the calculation to again underestimate the numbers.

So if my car coasts 1.307 units of distance getting 133mpg then thats 0.0098 gallons of gas used. 0.0098+0.0769=0.0867 gallons used over 2.307 units of distance. 2.307/0.0867=26.6mpg.

So:
30mpg FAS
26.6mpg Nice-on
12.7% difference

But I've been getting 30mpg with nice-on coasting, so I'm gonna keep doing some more guesses with Fasing and see how they compare with nice-on till I get something close to what I'm doing.

I'll leave all the calculations out and just put the results below:
pulse:glide ratio

1:1.3839
31mpg FAS
27.3mpg Nice-on
13.5% difference

1:1.4608
32mpg FAS
28mpg Nice-on
14.2% difference

1:1.5377
33mpg FAS
28.7mpg Nice-on
15.0% difference

1:1.6146
34mpg FAS
29.4mpg Nice-on
15.6% difference

1:1.6915
35mpg FAS
30mpg Nice-on
16.7% difference

1:1.7684
36mpg FAS
30.7mpg Nice-on
17.3% difference

1:1.8453
37mpg FAS
31.3mpg Nice-on
18.2% difference

1:1.9222
38mpg FAS
32mpg Nice-on
18.75% difference

1:1.9991
39mpg FAS
32.6mpg Nice-on
19.6% difference

1:2.076
40mpg FAS
33.25mpg Nice-on
20.3% difference

So as we can see, the longer you glide, the more of an impact FAS has vs Nice-on. Now with me averaging around 30mpg with my city driving, I should be able to get around 35mpg if I start doing fas. On one road I hit 40mpg, I wonder how high that would be if I fas'd down it instead.

The only problem that I have is that my scangauge doesn't shoot to 9999 during a FAS, instead it still displays the same numbers as during a nice-on coast but also updates much slower, also it doesn't record all of the distance traveled. So if I do my next tank with fasing, my sg is going to be under estimating what I'm really getting. And also, my lights all turn off when I key off, so no Fasing after the sun sets. I don't care about the daytime running lamps flashing though.

[BudgetFitting]

Very cool.

I did 44.5 mpg tank average with nice-on, compared to 57 mpg tank average with FAS in my Fit. Both with the same P&G cycle and coasts.

This tank I am extending the coasts and am shooting for 60+ mpg.

[lightfoot]

Originally Posted by bomber991

And also, my lights all turn off when I key off, so no Fasing after the sun sets. I don't care about the daytime running lamps flashing though.

Ditto here. Check on your WRX, but on my Outback when I key off the DRL's go out and stay off even when I key back on, and don't come back on until I restart the ICE.

If I have the headlights on, they go off when I key off but come back on when I key back on, so there is just the momentary flash off. So I simply drive with the headlights turned on (what's the diff, the DRL's are on anyway?). I wish we didn't have all this fancy circuitry!

Also, beware: in the Outback if I don't push down the clutch, let off the gas, and wait for 0 GPH to appear in the SG BEFORE keying off, a spurious huge GPH number like 8.8 GPH can pop up later during the FAS. The only way to get rid of it is to restart the ICE. Even if you do as described, a smaller spurious 0.2-ish GPH number can pop up after about 15 sec of FAS but you can get rid of it by kicking the gas pedal to the floor once. The smaller spurious number may not affect the aMPG but the larger one definitely does.

Yes, the SG does take a while to update, which may affect the numbers during the transient things we do.

[CitrusInsighter]

This is an excellent thread with very valuable insights. I will be sure to point any newbies with doubts about the real-world benefits of FAS to this thread.

[PaleMelanesian]

Cool! Numbers. I like numbers.

Keep in mind that this is only for the P&G cycle. Averaged into a whole trip, with maybe 50% of the trip in P&G, the difference will be proportionally smaller. Still significant, but less of a difference.

MetroMPG did a driving test to compare, and found a 12.9% difference. http://www.metrompg.com/posts/coasti...-vs-idling.htm

[phoebeisis]

I get your drift, but I think my pulse glide ratio from 27-35mph is more like 1:6- 1:8 .
I spend maybe 3-4 seconds getting from 27-35 and no less than 24 seconds coasting down.
I'm accelerating for maybe 13-170 ft and gliding for over 1000 ft. I understand you are just using it as an example. The longer the glide, the more dramatic the savings by shutting down.

Your ratios would be a much higher speeds,I guess.

I glide with ICE on in D not N, but that is because a pecularity of GMs ATs-they glide forever with no engine braking until I hit maybe 24 mph or so when I can feel the trans re-engage. Shutting the motor off is just too tricky for me - no question it saves fuel , of course..
Charlie

[JusBringIt]

I think with aero mods, hs pulse and glide Ice-off pays off quite well. with basjoos' civic for example. I could have a delta of 45-70mph and have an extremely long glide distance. What this would be very good for (at least it has been in my case) sometimes there's a dip and your car might drop speed too much before it crests after the dip, so then you have to turn your ICE back on. With this improved gliding distance you can make it over the dip and get a second segment w/o ever having to go Ice-on.

I noticed this helped my final trip mpg tremendously.

[some_other_dave]

I agree with phoebeisis about the "glide ratio". It sounds like I'm not gliding as well as s/he does, but even so I spend 1-2 seconds in pulse, and 10 or more in glide every time.

I found the difference in my case to be pretty dramatic; P&G with FAS seems to be the largest single contributor to my MPG after slowing down.

-soD

[WindPower4ALL]

Great work. Unfortunately it consumes fuel to start ICE back up after FAS so at least for me, FAS distance or time at a light is also a major consideration... I've been FAS with great success but my mileage took a pretty big dip when I started turning my ICE off at red lights.

I haven't broken my SGII out yet; I wonder what a normal amount of cranking fuel is.

[JusBringIt]

older engines use significantly more fuel to start as with larger vehicles, if you fas up to a light, you should gain on a fas, not lose, the sg and a couple aero mods can get you over 30mpg in your silverado