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Old 12-01-2007, 03:06 PM   #51
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Quote:
Originally Posted by brucepick View Post

(I copied the link address and opened in a separate window to see graph full screen.)

And thanks to you, Mira!
No problem!

Quote:
Can you give me more information so maybe I can understand the chart?
Specifically, what is the meaning of the scale on the right (values shown .70-1.70)?
The link I posted earlier explains it all, although I'll explain it. Those numbers mark the value for the particular lines that are nearest. Those lines are isopleths, contours that have the same value, in this case, BSFC (brake specific fuel consumption). Which is basically efficiency, or mass of fuel/energy output of engine, in lbs/(horsepower hour). So the smallest island is 0.42, then 0.45, 0.50, 0.55, 0.60, 0.70, 0.80, 0.90, 1.0, 1.7. Those last 5 values were what you were asking about.

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And where do I/we see these in the graph:
2000 72%
3300 74%
3600-4500 70 - 100%

Percent of what? Where is it shown in the graph?


Sorry, the graph was actually in that link, but I'll post it here for everyone to see (immediately above). I also posted it in my spreadsheet for calculating pulse and glide, and regular steady state cruising fuel economy here.

Anyway, you will see some dashed lines on that graph, 5%, 10%, 20%, 40%, 60%, 80%, 100%. That is % of maximum power. This is one of the easiest specs of a car to find. Notice that maximum power is only at 1 point in the graph, at about 5300 rpm. So if you have an engine map for your car, or something roughly similar, you can tell how much actual power your car is producing at that point in the engine map by multiplying the max power (hp or kW) by the % power at that point.

So, to get 72%, 74%, etc, I was just interpolating values between islands.
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Old 12-14-2007, 06:01 AM   #52
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Many thanks, Mira.

I looked at the central isopleth a bit.
What I see is of course first, the central point is right about 2000 rpm.
And as you increase or decrease rpm from the center point you reach the isopleth ring pretty quickly.
However as you increase/decrease load at 2000 rpm, you have a good distance to go before you reach the ring.

Of course, it's just a graphic and changing the scale would change the shape of the central blob. But anyway you can make a case to not worry about load too much as long as it remains midrange, and try keep the rpms near the center point.

In my case with an auto tranny without lockup, 2000 rpm is about the lowest I can run it when cruising over 50 mph before it downshifts. It's pretty happy at around 2100/2200 so I often run it there. I can keep it in or near the optimum range, but I have to pay attention.

Thanks again!
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

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Old 12-31-2007, 01:09 PM   #53
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Overlooked the obvious

It's funny that I haven't seen one person put something up about trucks. I read this entire thread and signed up just to post this.

2-3 MPG - put tailgate down.
3-5 MPG - remove tailgate.
1-3 MPG - put in one of those aero nets.

I've noticed several people talk about indexing plugs, but I've had terrific luck with Bosch +4 plugs.

Amsoil. I swear by the stuff. If your rig has the room, definitely get the externally mounted double oil filter.

1998 Nissan Frontier, 182K miles, 2.4L DOHC engine, 5-speed manual. Amsoil since I bought it, Bosch +4s, had tailgate up less than 25x in six years (2001-2007). Nearly new when I bought it. I averaged 32 MPG. Highway, actual real-world miles - 36 MPG, about 120K of those miles.

Wouldn't drive it over 60, and it could tow a 12-foot U-Haul trailer 1800 miles, both springs on truck and trailer bottomed out, never went below 40 MPH and 3rd gear. All this with a 3025 pound curb weight. Turned A/C off or removed it from belt system (different belt, A/C hooked to other items) for best mileage.

I MISS that truck.

Stock was 22/26. Revised EPA estimates 20 city/24 hwy. Yes, I really could get 36 MPG out of that thing without the tailgate, Amsoil and +4 plugs. I did the same trips repeatedly (Seattle to Los Angeles and back, about once per month for three years) and found the +4s gave me about 3-4 MPG, same with Amsoil, same with the tailgate. Exact same stops, same gas stations, same time of day (better MPG in daytime), etc.

Thought you'd like to hear that one. BTW tailgate UP for snow and better traction.
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Old 12-31-2007, 01:09 PM   #54
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Overlooked the obvious

Edit: removed double post
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Old 12-31-2007, 02:48 PM   #55
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well that depends on the size and configuration of said truck. lets say a regular cab regular bed s-10 compared to a full size quad cab regbed dodge ram or somehting.

not to mention all the different cabs: quad, extended, regular

then beds, short, long, regular, fleetside flareside

then full size or compact pickups.

then all the different brands, some with smooth curved fronts, others flat boxy fronts.

so what works with one might not with others ya know? just like cars...
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Old 01-01-2008, 11:39 AM   #56
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...i think he forgot to say his tailgate was about 12' tall
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Old 01-12-2008, 11:33 PM   #57
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Don't drive if you can walk. It's not only good on gas, but it's better on your waistline.
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Old 01-15-2008, 11:35 PM   #58
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Hello, very nice forum here. My very first post.

I was wondering if changing to manual transmission should be on the list. Manual transmission is always lighter (at least in the cars I know). I have always thought about manual transmission as more fuel efficient in general, though I have never seen any real studies.
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Old 01-16-2008, 12:32 PM   #59
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maybe but LOTS easier to coast with manual, will last forever, can upshift downshift and prepar for upcommin road events, engine brake quicker and more while going downhills (maybe not a BIG advantage gas wise cuz an auto can do the same but maybe save on brakepads etc) dont have to do 30k fluid changes just every 100K swap fluid so you may save on not having to buy filter+gasket+fluid every 30K or so.

plus even if you have a slow car it can seem fast and fun with a manual tranny.
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Old 01-24-2008, 08:15 AM   #60
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Thanks for all the tips. I'm very interested in any cheap way to increase mileage.
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