You guys DARKEN UP!


your trucks.

I hear BLACK is a good color

;D

SWEET

 

[quote author=Hoss link=board=20;threadid=18317;start=0#msg171930 date=1060784211]
[quote author=cp link=board=20;threadid=18317;start=0#msg171827 date=1060745208]Lighten up yourself. [/quote]

I AM lightened up you red necked, yellow bellied, ring tailed, sap suckin', snow blowin' egg head!!!! ;D

There....now I feel better. ;D :P


[/quote]

You really shouldn't hold back like this...Tell the man how you really feel :

 

;D

 

ok, boys, since the original question had to do with real fuel economy sweet spot, rather than other intangibles contributing to the man/machine relationship, I'll take a stab at the objective side of this.

I propose that at a given HP output, the engine does indeed have an optimium rpm range for best fuel economy. Such an efficiency curve resembles the peak torque curve and is somewhat corrleated to it.

At low rpms, friction losses consume a large portion of engines HP. Also, a low rpm engine is a very poor energy source due to the small combustion chambers, small number of strokes per minute and the small volume of air that the engine can move. so more energy from the fuel goes out the tailpipe instead of to the crank.

At high rpms, the engine has to overcome some very high piston accelerations (especially for long stroke engines) as well as the mechanical limits of the valve train including the cam.

As for the vehicle itself, there is no sweet spot. HP requirements increase as the square of vehicle speed, so faster is always less efficient. At slow speeds, friction losses dominate and wind drag is very small, so in that case faster is better. But for real traveling speeds, speed gobbles HP

So what this means is that the driver picks the vehicle speed, whatever that is to acheive travel goals, and the gears (should be able to) pick the right rpm, generally believed to be in the 1700-2000 region. Hence the success of after market over/under drive units which reportedly claim 20% improvements in economy for towing. more gears are better.

In actual practice, most of us have 6 gears or less, so we DO have a vehicle speed component that contributes to the sweet spot thing.

 

So.....there IS a sweet spot then, right? :P

 

SWWEEEEEET Spot for mileage towing for me is 2,000 rpm
go a bit slower and I guess I negate the combo of HP and torque that give it better mielage in tow at 2000 RPM.
I lose about 1mpg below and 2 mpg above 2100 RPM.

empty the RPM range is a little bit greater changes and I do get better mileage at 55 mph but I don't drive that speed on average.

I believe when the engine is working...towing...it is optimizing what I got the diesel for.

SWEETER

 

But the real question relates to the effect of color on the sweet spot. the darker the color the sweeter it is!

seriously, I was just starting to wonder if the towing sweet spot might be a bit higher in rpm than the empty sweet spot. thanks for the confirmation, Scotty.

 

My truck seems to operate best between 65-70 mph. With the 4:10's that places me right at 2k rpm. I think thats the best compromise between "fuel efficiency" and "towing performance" Obviously, the slower you go, aka fewer rpm's the engine is turning, the better fuel economy you will get. (to a point) but you also risk hurting the engine by lugging it too hard. I hope that I've given the correct input to the original question, after all the technical information I've read, I kinda lost track of ....what was I saying???

Cat Cracker.

 

[quote author=Doug link=board=20;threadid=18317;start=15#msg172031 date=1060797994]
ok, boys, since the original question had to do with real fuel economy sweet spot, rather than other intangibles contributing to the man/machine relationship, I'll take a stab at the objective side of this.

I propose that at a given HP output, the engine does indeed have an optimium rpm range for best fuel economy. Such an efficiency curve resembles the peak torque curve and is somewhat corrleated to it.[/quote]

Sort of. Specific fuel consumption curves are, for all practical purposes, flat. To have a 'sweet spot' it would need a valley, though, not a peak.

This is all accounted for in the sfc graph.

I don't understand the next to last sentence. Faster is better at slow speeds? Also, horsepower required increases proportional to the cube of vehicle speed, not squared.

If we define 'sweet spot' to mean something intangible such as a pleasant exhaust note, then by all means, there probably is one. But as far as mileage goes, faster always means less.

 

[quote author=Hoss link=board=20;threadid=18317;start=15#msg172051 date=1060799747]
So.....there IS a sweet spot then, right? :P
[/quote]

Awwww Hosssss......... :-*

 

[quote author=cp link=board=20;threadid=18317;start=15#msg172162 date=1060816759]If we define 'sweet spot' to mean something intangible such as a pleasant exhaust note, then by all means, there probably is one. But as far as mileage goes, faster always means less.
[/quote]

Not necessarily. Going 20 mph at 1000 RPM's will yield less MPG than going 65 mph at 1900 RPM's.

 

[quote author=spots link=board=20;threadid=18317;start=15#msg172177 date=1060818038]Awwww Hosssss......... :-*
[/quote]

Didn't I hear someone say you were a girl??

By the way...nice signature. ;D

 

Mine seems to be to the floor but thats just me. : close to 2800rpms or higher
DM01

 

Hoss, you are a mess. We luv ya, man.

Mileage wise, I seem to get the best on the road at about 55 mph (4.10 axle). I am pushing around 23 mpg at that speed. It quickly deteriorates to 19 at 70. Sweet spot as to humming along, that intangible, ungraphable (hey, new word), speed at which all seems well in the world, I would put it at about 70.

Now, if I get out the slide rule, plot the curves for the exponential rise in resistance to love bugs hitting the windshield with the speed at which they hit and whether or not they are pregnant when they hit, now we have an ungraphable equation. (I just had to use that word again). ;D ;D

 

<Such an efficiency curve resembles the peak torque curve and is somewhat corrleated to it>
My overhead trip computer does not suggest a flat fuel consumption curve, which is why this subject is of interest to me. Also, I'm refering to an energy efficiency curve (units in percent) which would peak if there is a fuel economy sweet spot. I'd be interested in seeing an sfc curve for the 3rd gen CTD. Do you have one? The only information I have on the 3rd gens is that usage at 2900 RPM and 305HP is on the order of 10% more fuel efficient than usage at 3200 RPM and 233 HP. Thats interesting, but not very useful in this inquiry

<As for the vehicle itself, there is no sweet spot. HP requirements increase as the square of vehicle speed, so faster is always less efficient. At slow speeds, friction losses dominate and wind drag is very small, so in that case faster is better. But for real traveling speeds, speed gobbles HP>yea, my oversight. wind drag increases as the square of speed and I forgot about the linear friction component which turns the polonomial into a cubic.

The reason faster is better (for fuel economy in miles per gallon) is that for slow speeds and low HP requirements, a greater portion of the engine's HP is used to overcome friction of all the moving parts (including the engine) instead of moving the vehicle. If that were not true, then the overhead mpg indicator would read 18 mpg while crawling in 1st gear.