I feel the only way to "debunk any myth" is to take every little conceivable possible anomaly out of the equation which is impossible. I think this thread was entertaining and very informative (scientific wise) but certain individuals like to make it a habit of souring a good debate.

Not pointing fingers.

 

I agree with the group that thinks 2 tanks isn't enough testing to come to a conclusion on the mpg. I check my truck every tank.I fill it to the top of the filler neck. Even by doing this I doubt I'm getting the exact mpg. I think you would need a extra tank that you could monitor the exact amount of fuel used on each test.Plus the test would have to be run under the same weather conditions & on the same course.My truck averages 18 mpg by my hand testing. Its best mpg was 22 highway with 75 mph being my top speed on a 400 mile all interstate highway trip. I used the cruise most of the trip. I made no fast starts & took my time when I passed cars on the highway. I've made the same run with my Grand Marquis & got 29 mpg. Its all flat highway I 40 between Memphis & Little Rock.The car really surprised me with its mpg numbers. I knew it got good mileage but it was about 4 more mpg than I expected.I want one of the scan gauges mentioned in this post. I'd check my mileage every tank & use it to find where my truck got its best mileage.

 

I responded to the "just pull numbers out of thin air" comment that challenged my assertion many standards we use were based arbitrarily. In Watt's case defining HP as the power of a particular horse. Its not well known even what breed of horse, let alone it's particular strength. History suggests that Watt used a draft horse, a breed that is dramatically larger & stronger than most horses & that this animal was harnessed to a mechanical device that converted muscle power into rotational power for Watt's experiments. I posted the alternative of a dog on a treadmill, Watt could've used a common treadmill too, but may have used a device like a turnstyle. For Watt horses from Shetland ponies to Clydesdales were commonly found harnessed to such machines, as well as dogs, goats, mules, donkeys & oxen.

Please feel free to try to edit & correct Wikipedia on "Horsepower is not a unit of power." Google 'horsepower' & the 1st thing you see is 1 HP=746 Watts, then the 1st sentence in the 1st entry (Wiki) states "HP is the name of several non-metric units of power". Also let the POWER company know that the kilowatts they sell me are not POWER. Then try to correct the standard reference 'Handbook of Chemistry & Physics' which under "Definitions" for "Power" lists "Units of power", "the watt, the horsepower". Finally lead a campaign to have the POWER taken out of HorsePOWER.

IMO avator did an adequate job of explaining what he meant by the "gas mileage myth" & page 6 is really late not to be sure what the Topic is.

 

After 7 pages & much derailing, reviewing avator's claim might be useful, especially since we haven't heard from him lately:

Upon review I don't recall anybody pointing out a glaring variable "then refilled from another station"! It appears avator didn't even use the same fuel both ways when he "ran this as a test"! Its nearly 200 miles between Huston & San Antonio, he had to refill before returning to estimate 1 way useage & may have been able to minimize this variable by carrying a pair of 6 gallon gas cans filled w/same fuel as he started out. Its not even clear if he used the same brand of fuel.

At this late point I'm curious if anyone still agrees w/avator & believes he's "debunked" what he considers the "gas mileage myth"? If anybody wants to help support his claim, there's a "gas mileage myth of driving slower saves gas" specifically in an F150 going 62 oneway & 75 the other, OR more generally, during normal 'high gear' cruising, for average vehicles, driven as they were designed to operate-let's hear it.

Anybody? Anybody at all? Or is it possible to find consensus on FTE, where everyone agrees w/the generally accepted wisdom, that driving faster consumes more gas, certainly in the common 62-75 MPH cruising range & that it is not a "myth"?

 

I guess that sums it all up. Club wagon has addressed all the issues here. I'm gonna do some tests... I think I know where a ox is; I got a dog; where can I find a goat....

 

Hopefully, it should at least lay to rest any lingering debate claiming "Horsepower is not a unit of power". I presume nobody has "issues" w/pointing out avator used different gas on each leg when he "ran this as a test" & the implication this fact alone could easily invalidate his conclusion?

Sarcasm has a place, as long as you realize that Watt might've just as easily used an ox, mule, dog, or goat as the basis to estimate his "unit of power". We could've all ended up talking oxpower, mulepower, dogpower, or goatpower had Watt arbitrarily hit upon a different working species or been raised in another part of the world. More importantly, those alternative units would be as valid as horsepower & demonstrate the arbitrary "out of thin air" nature the concept was based on. No 2 random horses are likely to have the same power & dwarf horses aren't even in the same ballpark as Watt's draft horse. Had Watt's whim arbitrarily chosen a Quarter horse or Welsh pony for estimates, his horsepower would've represented dramatically less power & skewed our numbers.

Do you still need to "do some tests" to become "really sure" what avator's "gas mileage myth is" & post an opinion on whether he "debunked" it?

 

What would we have had if Isaac Newton sat under a grape vine?

 

Where are you getting 19 miles per gallon? Let alone a staggering 24....Down a hill. I'm getting about 13-15, and if you're almost doubling that I'm going to need to make a purchase or two. I've also got a 99' 4.6 V-8. I've got the K & N air filter. I've also added the Tornado to the intake. At 4.00 a gallon I would love to make the modifications you're talking about.

 

Everyones truck is different, all kinds of variables as has been stated several times with people getting good/bad gas mileage. Id say at 13-15 your pretty average. Ive got a 5.4L with 35s and 4.56s, I usually average 13 and my best was 16.5 on the highway. Their trucks...not made for great mileage!

IMO...use that Tornado as a gun target. And also, I get better mileage with my stock intake and filter than I did with a "cold air" which is really a "hot air" intake! Your paper filter works fine!

 

Thanks for providing another example that illustrates my point about the arbitrary "out of thin air" basis of many manmade units of measure. Newton's theory was independant of the apple, "a grape" or coconut falling would've been just fine. Has absolutely no bearing on the physical principles observed, BUT if applied as the basis of units of measure, would make a difference in the abstract numbers we assign.

Of course in this case the unit of measure was not based on an apple's mass/inertia, or named after an arbitrary choice of fruit or animal. Gravity came to be measured in units named after him-Newtons, just like units of electrical power are called Watts. Man is free to make up any number of different scales to measure the same things, invent units of measure & arbitrarily assign values, that's why the numbers are abstract.

 

I am not sure if this was really mentioned, as I kind of got lost in some of the arguments, but I feel the point to take away from the HP & TQ being numerically equal at 5252 isnt the specific numbers but rather simply that HP is a calculated value based on torque, they are a fixed relationship and cant deviate from this. Some seem to think they are both measured values and independant of each other. If you know one, and the rpm, then you can calculate the other.

As for the OP as so many others have said the test was not over a large enough distance, and plenty of other factors too. Generally speaking on the highway, wind resistance is the biggest factor so generally you get the best mpg the slower you go in the top gear. Of course there are some exceptions. I often drive pretty slow attempting to save gas. However on one stretch I often take if I drive through the county, my truck with hwy gearing, 33" tires, and a wimpy v6 struggles to maintain speed going up hills at 40-45mph on 5th gear. I mean the rpms are so low I could put the pedal all the way down and still be decelerating. However if I did 55-60 the extra engine power seems to not struggle nearly as bad. In that situation i'd almost bet I am getting better mpg cruising at 60 than I would be at 40 with the pedal mashed down (or constantly downshifting). I have no actual data for that though (yet) so thats just a WAG.

With an 80mi round trip for me daily to work on the hwy I plan on trying to do some mpg experiments myself to the best of my ability. So far I am getting extremely consistant results hand calculating (last five all within .1mpg).

 

It's due to the scaling differences of HP and TQ on the dyno graph. But yes, all HP and TQ curves intersect at 5252, and for engines that don't spin that RPM they too would intersect at 5252 if they they could spin to that RPM.

Look at the formula for HP.

 

again, the torque and HP curves "meet" or "intersect" at 5252 only if the curve is drawn that way. what you mean to say is the numerical value of both is the same at 5252 due to the formula being the ratio of ------rpm/5252

 

The reason the curves meet at that point on all graphs drawn as such, is that scaling on a single X and Y axis is used for both <both> curves.
It has noting to do with the curves themselves no matter if it's 10 hp or 1000 hp and their attending torque curves, the same scaling is used for both, they will cross at the same point.
The only thing you can get from a torque curve is the straightest portion of the curve indicates the best motor efficiency in terms of RPM which is the measure of it's total max. ability to injest air.
At the point the torque curve begins to flatten and fall, the motor's ability to injest air is becoming limiting due to such things as cam timing, port flow restrictrictions, exhaust restrictions etc.
Only reason HP may keeps rising is due to the RPM allowing the motor pass more air through it even though the torque is falling, then even HP begins to become restricted and falls as well because then even high RPM cannot keep forcing more air to flow through for the same reasons the torque falls much earlier in the RPM range..
Said another way, if you look at the torque and HP drawn on seperate graphs, the relationship is only to RPM and the value each attains anywhere in it's range and has nothing to do with 5252 at any time.
The term 5252 is just a convient factor to use in calculation of HP from recorded torque values.
After all, a motor only generates torque from which 5252 is a term used to derive the HP figure for the curve.
Said another way, the motor takes fuel expansion and converts it to rotational torque. This opertion knows nothing about HP that is only a derived math function.
</both>

 

hp and torque are not exclusive values. Torque comes first and hp is calculated from that. They are not independent values drawn on axis of same scale directly. It is a simple logorithmic relation.