Catch me if you can (MPG)

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Mopar1973Man

Mopar1973Man

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Here you go...

Gasoline 116,090 BTU per gallon / 3.919 = 29,622 BTU per dollar

Diesel 133,000 BTU per gallon / 4.099 = 32,446 BTU per dollar

Diesel still is a better deal...

As for the rise... RV275 injectors, Edge Comp (5x5), and learning how to drive again...
 

ramhunter9

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Now with the mods I have put in I am down to 17/21
Still not bad IMO
 
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Mopar1973Man

Mopar1973Man

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Knowing you've got larger tires how are you getting your distance number correct?

Percentage offset or using a GPS?

With weather at about -2*F for starting low and +22*F for a high and travel all the way to Ontario, OR get some stuff and head home. With my list of mods and running my 265/75 R16's I pulled... Cmg is my round trip... Tmg was from Ontario, OR to home...

attachment.php


Still I think I got you with even colder and nasty weather...
 

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rambob

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I want to get one of those gauges.
would probably pay for it self rather quickly if you (I) could learn to drive from it.
 
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Mopar1973Man

Mopar1973Man

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I want to get one of those gauges.
would probably pay for it self rather quickly if you (I) could learn to drive from it.

Worth every penny... Yes you'll learn that your driving style, mods, tuning, etc. all have a effect on MPG's. Funnier yet the ScanGauge II is more accurate than hand math because the SGII is calibrated and corrected for both speed / distance and fuel flow with my mods. Where my speedometer is off by 0.5 MPH so the odometer is off by about 20-30 miles per tank.
 

Stangshcky12

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Here you go...

Gasoline 116,090 BTU per gallon / 3.919 = 29,622 BTU per dollar

Diesel 133,000 BTU per gallon / 4.099 = 32,446 BTU per dollar

Diesel still is a better deal...

This caught my attention so I looked into a little bit more. Pressure and temperatures a big variables on both fluids. I double checked the NIST values with the AFDC values, gasoline Is 116,090 btu and diesel is 128,450 btu
The current national average of gasoline is $3.483 so 33,330.4622 btu/dollar
Average of diesel is $3.888 a gallon so 33,037.5514 btu/gal

Unfortunatley the government will always tax diesel fuel so it's price per btu is similar/ less efficient then gasoline
 
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Mopar1973Man

Mopar1973Man

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Careful with the diesel BTU value it varies in repect to cetane level...

Using ASTM testing scale for my local summer and winter fuels... Lower the cetane the more BTU's. :naughty:

cetane-btu3.jpg
 

rambob

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if your odometer is off due to larger tires, the hand figures off in what direction?
 

Stangshcky12

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Maybe with your additives, in that case you have to consider * API gravity, distillation range, sulfur content, stability and flash point to determine BTU content since cetane isn't a measure of fuel quality.
ASTM is not the standard for energy properties NIST is. ASTM did set the standard cetane level at 40 in north America (which is the minimum level recommended by almost all diesel engine manf.) using different cetane levels then the manufacturers doesnt always result in better efficiency. Any graphs I've ever seen no. 2 diesels performance and efficiency both plateau at 55.
512eadc5.jpg
Hopefully this works, this is from the dept of energy and matches NIST
http://www.afdc.energy.gov/afdc/progs/fuel_compare.php
Do you have a link for that graph or the information. I'd like to look into it more
 

Rogan68

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Knowing you've got larger tires how are you getting your distance number correct?

Percentage offset or using a GPS?.


Before I got the Edge Juice w/Attitude, I noticed that my larger tires vs speedo wasn't linear.. sub 30-35mph, the speedo was on the money with the gps. as I went faster, the speedo started to lag.
 

Stangshcky12

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Before I got the Edge Juice w/Attitude, I noticed that my larger tires vs speedo wasn't linear.. sub 30-35mph, the speedo was on the money with the gps. as I went faster, the speedo started to lag.
The speedometer is off by a percentage when increasing tire size. A 31-35 will cause the speedometer to be off about %10 which is why it is more noticeable at higher speeds.
I'm just guessing here but to figure out the odometer difference you would use to divide a mile by circumference in ft. And get how many rev. your tire does and divide it by what it did
(31"*pi)/12= 8.11583333 ft/rev
5280/8.11583333= 650.580142 rev/mile
(35"*pi)/12= 9.16 ft/rev
9.162978577 = 576.231839 rev/mile
That's about 12.902% or for ever 1 mile on your odometer, you went 1.12902 miles

Orrr you could just divide new tire size by the old and you can get the difference.....Lol
 
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Rogan68

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My stock tire is 245/75-16. I've got 235/85-16s on it now. 4.1% offset.

245/75-16:
30.5" dia.
7.98 ft/rev
662 rev/mi

235/85-16:
31.7" dia
8.29 ft/rev
636 rev/mi


662 / 636 = 1.0408, or 4.1% (rounding)

60mph + 4.1% = 62.46, or 62.5mph.
 
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Mopar1973Man

Mopar1973Man

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So how do you explain that I'm currently running a stock sized tire 265/75 R16 and my speedmeter is off by 0.5 MPH and total trip difference for a tank of fuel can vary 20-30 miles? GPS and ScanGauge II are right on but the odometer is off???

As for the cetane grid I got it from a ASTM document... I had a connection with a guy that allowed me to grab it... But this is all I got left of that document... I lost the document in one of my hard drive crashes.
 

Stangshcky12

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I might have to go to the library this weekend and see what I can find there as far as ASTM standards on this.

How many miles a tank are you getting? The speedo/odometer gears in your truck might be for 245/75/16 (everywhere list that as the stock size, although I'm not doubting that 265/75/16 may have been an option) so if your using 25-30 gallons a tank at 19mpg and your odometer is off 3.73% your looking at 17.7 to 21.261 gallons a tank.
This is of course all nominal numbers and we know tires are not always ideal size and average mpg is ever changing.

As far as the speedometer, speedometers suck lol I dont really have much of an idea there. Ive driven countless vehicles from my cousins car dealerships and the speedometer was typically 3-5 mph faster then what the GPS read (which of course can be up to 1 mph off (older ones) newer ones seem to be .3-.4 mph off since they use several signals, not just four like old ones)
 
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Mopar1973Man

Mopar1973Man

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Thank you... That's what I want someone else to voice right there... So if your looking for true number you got a use a device calibrated for your application. Hence my setup of the SGII and GPS.

I know know that MPG's is just averaged numbers using the best information you can provide for the math. So if the information is skewed then so is the results.

As for the tires that would be a 2.3 MPH change so I'm right on the tires just the stock speedo/odo is calibrated poorly.
 
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