neutral coasting and engine load - Fuelly Forums

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Old 07-17-2008, 08:48 AM   #1
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neutral coasting and engine load

yesterday, I was playing around with the scangauge and I put it on engine load. I found some very interesting things.

there are some things I know to be true.

if all other factors are the same, the lower your engine load, the better FE

if all other factors are the same, the lower your RPMs, the better FE.

I noticed that coasting in gear let my engine load get down to as low as 7 percent. I understand that the reason for this is that the wheels are basically turning my engine at that point.

I also noticed that If I were at a stop light, my engine load was around 25 percent. I haven't tested this but I figure the same would be true if I were coasting in neutral.

when I tried the neutral coasting, I didn't get great results. I wonder if the fact that my engine load was higher actually took away from the savings. I do believe that the savings are there and that I did get a gain (just not enough for me to notice).

just for comparison purposes, when I am riding on fairly flat roads around 50MPH I am usually hitting 35ish percent as far as engine load.


I was more wondering if other people had thoughts on this one. I have never looked at engine load for coasting and for idling until now.
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Old 07-17-2008, 09:40 AM   #2
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Does your instant MPG go up or down when you shift into Neutral? In the Beast @ 35 mph shifting into Neutral the instant MPG will almost double. Stopped, in Neutral I read about 3% load. In Drive and stopped I read 5% or 6% load. Granted I have not finished my first tank yet, so my SG is not completely calibrated yet, but the numbers going up and down should still provide relative information.

-Jay
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Old 07-17-2008, 09:41 AM   #3
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My xB runs in the 40-50% load at a wide range of speeds in top gear but I have not looked at lod when engine braking / coasting . . . sounds interesting. Another thought I had was that an electric motor connected to the engine all the time as a starter-alternator-motor would not allow you to really run on electric alone but it may have enough to spin the motor at idle when stopped or coasting and get the engine into fuel cutoff!!!! It could also keep the alternator putting out power to the 12 volt system and the AC could also be running without burning any fuel running off a separate high voltage battery pack of course and when engine braking you could recapture the energy back into the battery.
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Old 07-17-2008, 09:51 AM   #4
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That "35ish" figure; is that for neutral coasting at 50mph or in-gear cruising at 50mph?

I wish my stupid ELM327 would come in from China already, it's been far more than "7-14 business days" by now!
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Old 07-17-2008, 09:52 AM   #5
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My instantaneous mileage jumps to over 200 which made me wonder first of all. when I did the neutral coasting (did it for an entire tank) the scangauge said that my average should have been around 43 for the tank. turned out it was 36.1 or so.

I have heard that the scangauge calculates MPG using air flow (not fuel flow) and this obviously threw my scangauge way off.

I just noticed this yesterday and haven't really played with it a whole lot. I think the reason that Jay's load is so low at a stop is because of the 350 vs the 4 banger.

*edit* the 35ish load is in gear cruising. I haven't done much of the neutral coasting thing since that one tank. I did notice that my tanks seem to be one good tank and one bad tank as per my gas log and that was one of the low tanks as far as the pattern goes and it was pretty high considering so maybe it did do a little
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Old 07-17-2008, 09:52 AM   #6
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Quote:
Originally Posted by JanGeo View Post
Another thought I had was that an electric motor connected to the engine all the time as a starter-alternator-motor would not allow you to really run on electric alone but it may have enough to spin the motor at idle when stopped or coasting and get the engine into fuel cutoff!!!! It could also keep the alternator putting out power to the 12 volt system and the AC could also be running without burning any fuel running off a separate high voltage battery pack of course and when engine braking you could recapture the energy back into the battery.
You can buy a brand new Chevy configured exactly like that right now, except it doesn't bother to idle the engine when not necessary (so it doesn't use the electric motor for that purpose).
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Old 07-17-2008, 09:53 AM   #7
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While you're experimenting, try putting it in park at a stop light. I hear tell that some transmissions unload the pump or something in park whereas they don't in neutral.
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Old 07-17-2008, 09:57 AM   #8
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I am actually riding with my buddy today so I don't have my car but tomorrow, I will definitely be playing with this some more.

I don't truely understand how much load affects FE compared to RPMs. there is obviously a trad off there to some extent. more than anything, I saw a pattern and figured I'd share.

I will try the park thing as well.
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Old 07-18-2008, 04:30 AM   #9
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riding to work this morning, I took some data. this isn't an experiment but more raw data that I took. I also want to mention that my car idles a little low (tends to jump a little at idle) so the numbers for that may be a little wonky.

going down hill, no pedal in drive__7-9% LOD
similar hill, in neutral____________21% LOD
stop light, drive______________21-25% LOD
stop light, neutral____________21-25% LOD
stop light, park______________21-25% LOD

it doesn't seem to matter what I am doing at a stop light, I always see the same. also, I realize that these numbers will be different for every car/engine combination. but I think the pattern will be similar which is more what I was looking for.
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