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Discussion Starter · #81 · (Edited)
The warmer the air, the less aero resistance you will get. How much that adds to mpg, idnk. Warmer intake air temps definitely = better mpgs... Just be aware of that fan clutch limit.

In general, the higher the ambient air temp is the less time it will take to get the truck heat soaked for the best mpgs. Meaning, differentials, bearings, transmission etc. all will give a lesser amount of resistance hot vs cold
Steve, what is your trucks "ideal" IAT?

I observed on my last 1300 mile trip differences in LOM mileage. In the morning mpg were less than in the heat of the day. Also, when I got up north, that evening temps dropped from 80s to 60s. LOM dropped in relation to IAT. Truck was heat soaked.

I looked at IAT changes as ambient went up and down vs. LOM reading. Naturally, IATs followed ambient temp. IAT was from 5 to 10 degrees F above ambient. Both of ambient and IAT sensors have been replace in the last 12 months.

Humid air is less dense than dryer air. Counter intuitive but the numbers don't lie.

Density of air

I race where a thousands of a second is the difference in winning or loosing. We look at all the variables. Other AIR variables that impact MPG/HP, temp, elevation, barometric pressure. Some folks have weather stations in their trailers to get track data vs. a weather station. It's that important.

I thought since these are compression combustion engines, there is an ideal charge temperature that produces the best MPG. To really know, a test should be run with constant elevation and barometric pressure. My trip to IL didn't take into consideration these two important variables.

My starting point elevation 643' and final destination 670'. Next trip I'll note elevation and B pressure each time I stop. I might have to get an assistant to enter the data as we drive!!

Yet, when I was driving to my final destination in IL, dropped off my load and started back south 50 miles in the evening, MPG dropped. Ambient dropped about 15 degrees. The next morning, in the 60s, truck lost MPG while it heat soaked. After it heat soaked MPG stayed about the same as that evening until later in the day. As temps went up, MPG went up.

Has anyone else notice MPG changes related to IAT or ambient temp?
 

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Discussion Starter · #82 ·
I'd forgotten all about the pesky drag :rolleyes: Seems from your comments then, that the MPGs effect of a 15-20 degree swing in ambient temp in Flatistan's Gulf Coast is likely negligible in steady-state cruising.
On a side, but related note; I will report that thanks to you guyz I spent $70 bucks on that black "air dam" contraption under the front bumper that was missing in my truck! But I'll make my money back in MPG savings right?... Right?... (1,000,000 miles later). Truth is I disliked how it looked without it. :cool:
View attachment 955175 View attachment 955176
I agree, your truck looks better with the air dam.

Yes it will payout. Today's fuel prices sooner than last year! o_O

I might take off my side bars and rear mud flaps on my next trip to IL. They look like more stuff producing drag.

I just replace my tonneau cover. It was 13 years old and had over 200K on it. Folks say this cover helps with MPG. I like to think so too and like to have my contents covered...
 

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I might take off my side bars and rear mud flaps on my next trip to IL. They look like more stuff producing drag.

I just replace my tonneau cover. It was 13 years old and had over 200K on it. Folks say this cover helps with MPG. I like to think so too and like to have my contents covered...
Thank you sir. All 4 flaps on mine are new. Hate the thought of every rock and piece of debris chipping away at the paint. Tonneau cover is on my list but starting with injectors, I have about $8k of "needs" ahead of it so it may be a few... hmmm... years! :D
 

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I'd forgotten all about the pesky drag :rolleyes: Seems from your comments then, that the MPGs effect of a 15-20 degree swing in ambient temp in Flatistan's Gulf Coast is likely negligible in steady-state cruising.
On a side, but related note; I will report that thanks to you guyz I spent $70 bucks on that black "air dam" contraption under the front bumper that was missing in my truck! But I'll make my money back in MPG savings right?... Right?... (1,000,000 miles later). Truth is I disliked how it looked without it. :cool:
I could probably stare at this for about a hour and a half and not get bored..



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All things equal, how much are MPGs influenced by ambient temperature? I understand there are a ton of variables and other factors also described in @steve05ram360 various posts, but if you were to take a ballpark guess, would you say 20 degrees make a difference? This morning I ran 300 miles round trip, mostly cruise control @70 (2050 RPMs or so, 4.10 diff), and I seemed to have gotten a 1 mpg difference between the legs. 18 vs 17 mpg. Only material difference was temp at 70F when I left at 6 AM and 85 F when I returned around noon. I know it is too short of a trip to really put too much weight on it, but since turbos like cooler denser air, I figure there is some impact. Or is the difference inmaterial unloaded at those RPMs making 7-8 PSI of boost with EGTs between 7-8k?

PS: Pardon if this has been already discussed but could not find a reference after limited searching
I might be crazy, but I think you have 3.73s. I’m pretty sure 4.10s run much higher at 70.
 

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I might be crazy, but I think you have 3.73s. I’m pretty sure 4.10s run much higher at 70.
You (and others) certainly know more about this than diesel truck rookie me. I am going by the factory Build Sheet "Equipment Listing" based on the VIN. See the particular section below. Everything else in the Build List matches. Also, every time I see peeps posting about speeds and tachs, it seems they always turn less RPMs than me. But I guess it is possible the original 4.10s were replaced. She did come with the taller than stock Falken 285/70/17 Rubitreks which should account for about a 2 mph offsetting difference @70. In any case, I would love to confirm from others that run 4.10s. If I do have 3.73s then ****... my MPGs really SUCK! :oops:
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Steve, what is your trucks "ideal" IAT?

I observed on my last 1300 mile trip differences in LOM mileage. In the morning mpg were less than in the heat of the day. Also, when I got up north, that evening temps dropped from 80s to 60s. LOM dropped in relation to IAT. Truck was heat soaked.

I looked at IAT changes as ambient went up and down vs. LOM reading. Naturally, IATs followed ambient temp. IAT was from 5 to 10 degrees F above ambient. Both of ambient and IAT sensors have been replace in the last 12 months.

Humid air is less dense than dryer air. Counter intuitive but the numbers don't lie.

Density of air

I race where a thousands of a second is the difference in winning or loosing. We look at all the variables. Other AIR variables that impact MPG/HP, temp, elevation, barometric pressure. Some folks have weather stations in their trailers to get track data vs. a weather station. It's that important.

I thought since these are compression combustion engines, there is an ideal charge temperature that produces the best MPG. To really know, a test should be run with constant elevation and barometric pressure. My trip to IL didn't take into consideration these two important variables.

My starting point elevation 643' and final destination 670'. Next trip I'll note elevation and B pressure each time I stop. I might have to get an assistant to enter the data as we drive!!

Yet, when I was driving to my final destination in IL, dropped off my load and started back south 50 miles in the evening, MPG dropped. Ambient dropped about 15 degrees. The next morning, in the 60s, truck lost MPG while it heat soaked. After it heat soaked MPG stayed about the same as that evening until later in the day. As temps went up, MPG went up.

Has anyone else notice MPG changes related to IAT or ambient temp?
On business travel and duty calls so short response, not enough time to catch up on thread...

Mine i found to be 100*-110* give fantastic results...
 

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I might be crazy, but I think you have 3.73s. I’m pretty sure 4.10s run much higher at 70.
Woke up thinking about this, and I ended up here: http://www.grimmjeeper.com/gears.html

Punched-in the numbers & the results seem to match 4.10s best. My tach may be around 100 revs lazy @70, while 100 revs over @75. Maybe at higher speeds the Mega DRW w/AT tires has all sorts of drag of drag, inducing more tire slip, making it show more revs than would be expected with the 4.10? Still 5-7% error range on a 16 yo tach-needle known to be "less than perfect". Speed is from GPS so I don't question that one.
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Steve, what is your trucks "ideal" IAT?

I observed on my last 1300 mile trip differences in LOM mileage. In the morning mpg were less than in the heat of the day. Also, when I got up north, that evening temps dropped from 80s to 60s. LOM dropped in relation to IAT. Truck was heat soaked.

I looked at IAT changes as ambient went up and down vs. LOM reading. Naturally, IATs followed ambient temp. IAT was from 5 to 10 degrees F above ambient. Both of ambient and IAT sensors have been replace in the last 12 months.

Humid air is less dense than dryer air. Counter intuitive but the numbers don't lie.

Density of air

I race where a thousands of a second is the difference in winning or loosing. We look at all the variables. Other AIR variables that impact MPG/HP, temp, elevation, barometric pressure. Some folks have weather stations in their trailers to get track data vs. a weather station. It's that important.

I thought since these are compression combustion engines, there is an ideal charge temperature that produces the best MPG. To really know, a test should be run with constant elevation and barometric pressure. My trip to IL didn't take into consideration these two important variables.

My starting point elevation 643' and final destination 670'. Next trip I'll note elevation and B pressure each time I stop. I might have to get an assistant to enter the data as we drive!!

Yet, when I was driving to my final destination in IL, dropped off my load and started back south 50 miles in the evening, MPG dropped. Ambient dropped about 15 degrees. The next morning, in the 60s, truck lost MPG while it heat soaked. After it heat soaked MPG stayed about the same as that evening until later in the day. As temps went up, MPG went up.

Has anyone else notice MPG changes related to IAT or ambient temp?
The 100~110 number I posted has always given me great mpg numbers regardless of the tune. Once upon a time i played with the IAT compensation tables to see if I could move that performance down to lower IAT temps and was not successful. The same thing holds true to the CTs... 200-210 seemed to be a sweet spot.

On elevation change, you could log the baro sensor on your next trip, might need to ensure there is enough disc space for the file or start and stop it at some interval, or set the logging interval to max so the file does not get to big for the operating system.
 

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I could probably stare at this for about a hour and a half and not get bored..



View attachment 955182
This truck would not benefit from the bed seals... I would predict more drag because of the rear fenders. If anything you could try a seal from the top down to the top of the flare line, thats just 4~6" or so, I doubt that will impact much.

I have been thinking of doing the trip wire on the rear axle tube on the bottom half of the tube (top half has the brake line IIRC). I would doubt that mod would do much by itself but with all the other aero mods, may add a small amount of drag reduction to the mix.





edit: thought just crossed my mind.. the rear axle tube is probably pretty dirty, I am wondering if that dirt is causing drag...
 
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Discussion Starter · #93 · (Edited)
The 100~110 number I posted has always given me great mpg numbers regardless of the tune. Once upon a time i played with the IAT compensation tables to see if I could move that performance down to lower IAT temps and was not successful. The same thing holds true to the CTs... 200-210 seemed to be a sweet spot.

On elevation change, you could log the baro sensor on your next trip, might need to ensure there is enough disc space for the file or start and stop it at some interval, or set the logging interval to max so the file does not get to big for the operating system.
Good info, again.

App Baro vs weather station Baro, is elevation and atmosphere. In then end, we would need to develop a spreadsheet to compare all the variables. Torque will log instanace mpg as well and would help confirm
external changes. I might do a few Torque logs on my next trip and compare the data.

In then gas burner world we use apps that calculate Density Altitude (Baro pressures, elevation, temp, humidity). We can predict performance base on this number. Counter to combustion ignition, internal combustion produces power when iat is lower. Folks "chase" low DA track days to run personal bests. I use to do this as well. Then I switched to burning Methanol. It's not a DA sensitive as gas.

Without a lab, measuring mpg mods is not that easy. Looking for the obvious works to a point. Many users doing one mod at a time and posting would be ideal. So far I have not followed my own advice. 😆
 

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That did not pan out on the Dakota when I increase IATs... mpg's stayed the same with the stock tune, 195* stat running at 203~206*
It’s what I found with several cars over the years.

Heat-stove pre-warmed air maintaining that range was best for steady-state cruise. Cars with 185-195F thermostats. It was part of emissions tuning from 1970 onwards (combined with heat crossover passage in the intake manifold).

— Fuel atomization at carb and maintained out to each cylinder.

The tweaks came with keeping the carburetor (fuel) cool while passing hot air thru it to an engine with a raised intake manifold temp.

EFI makes that last part easier.

.
 

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I agree, your truck looks better with the air dam.

Yes it will payout. Today's fuel prices sooner than last year! o_O

I might take off my side bars and rear mud flaps on my next trip to IL. They look like more stuff producing drag.

I just replace my tonneau cover. It was 13 years old and had over 200K on it. Folks say this cover helps with MPG. I like to think so too and like to have my contents covered...

— GM reports that Side Step Rails “help” (which is a surprise to the rest of us). I think it comes down to design thereof.

— Mud Flaps exert drag more noticeable on pickups than semis. Texas Flyswatter would be the substitute style of design.

Tonneau MPG improvement isn’t automatic. It’s best when half-open starting behind cab. Pressure equalization to both sides of the closed tailgate is the thing.

MPG against air temps is neither here nor there. Avoidance of traffic volume is the reason to start extra early (and finish for the day) as it’s the greatest penalty past fixed conditions.

Address-to-Address GPS navigation for each trip leg is: ideally, cruise control engaged at set speed coming down the ramp and neither throttle nor brakes used prior to exiting the Interstate at the ending address. The easiest method to replicate.

Unchanging test method
is Signal-to-Noise Ratio reduction.

As before, once 100% cruise control + set speed below commercial traffic is in use, the penalty phase are those periods from CC Off to CC On to exit and later re-enter the roadway.

1). Chasing cheapest fuel is where most screw up.

— The ideal fuel stop is the one right next to the entrance ramp.

2). Not investigating each stop via satellite pic ahead of time is the second big mistake.

— Some planned stops are less-desirable than others. Farther off the road than normal is one for Rest Areas. A fuel stop at a highway junction with a great deal of retail or a major factory type of situation = too much traffic.

Both 1 & 2 are how one learns to trip plan.

— They’re time-wasters (which effects my sense of momentum), they’re riskier (higher propensity for damage), they cause undue wear via throttle, brake & steering inputs (a better choice of stop eliminates this), and there is no offsetting $ fuel savings that shouldn’t have been done during Daily Driver Miles.

** Buying fuel at Wal-Mart flat off-limits as an example of How Not to Do It when combining the very worst of 1 & 2.**

To back into that again: get the City MPG higher annually and there’s no savings on a road trip justifies chasing a few pennies.

Plan Every Stop
Start & Stop Early
100% CC


My opinion is that these three constitute adequate changes to ensure relative highest MPG. Chasing more tenths of a mpg entails higher stress and results which vary too much one trip to another.

— Doing each of these well has more detail which experience will light up.

.
 

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Discussion Starter · #96 ·
It’s what I found with several cars over the years.

Heat-stove pre-warmed air maintaining that range was best for steady-state cruise. Cars with 185-195F thermostats. It was part of emissions tuning from 1970 onwards (combined with heat crossover passage in the intake manifold).

— Fuel atomization at carb and maintained out to each cylinder.

The tweaks came with keeping the carburetor (fuel) cool while passing hot air thru it to an engine with a raised intake manifold temp.

EFI makes that last part easier.

.
Gas Burners:
We have found 180F ish ECT makes more power, MPG, OEM T Stats, +-200F.

Chassis, engine dynos and drag racing gives the opportunity to hold many of the variable constant and change one at a time. The Dyno software has built in weather info and provide SAE data. Makes it easier to compare to other dynos.

Racing, we can control ECT with Rad electric fan and electric water pump. With standalone ECUs PWM and SS relays we speed up and slow Rad fan and water pump.

Each engine combo has a sweet spot ECT. Normally between 160 and 190.
 
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