I do believe this is the oldest discussion which has been revived . . . as of yet
It’s pretty disappointing that somebody would go to all the trouble of joining this forum, just so they can talk smack
Sounds like this guy may just have an inferiority complex
In my opinion, if you’re the new guy, you should test the waters, see how others are interacting, perhaps sit back and observe for awhile, before joining in
If you just storm into the place, guns blazing, you sure won’t make many/any friends
My wife’s Honda Element gets amazing gas mileage when we take it to Taos, NM. Here in central TX, it normally gets 22-23 mpg. Once we spent an entire week in the Taos NM area and drove all over the place. I got over 30 mpg, a combination of high altitude and slow speed limits on those national forest roads.
And no pinging at all with their 85 octane gas.
Visiting a region of high altitude also temporarily increases the pressure in your tires just like the pressure in your inner ear increases when you go up in an airplane. This may also contribute to better gas mileage.
Not sure why but this reminded me of the humorous college application:
Are there any significant experiences you have had, or accomplishments you have realised, that have helped to define you as a person?
I am a dynamic figure, often seen scaling walls and crushing ice. I have been known to remodel train stations on my lunch breaks, making them more efficient in the area of heat retention. I translate ethnic slurs for Cuban refugees, I write award-winning operas, I manage time efficiently. Occasionally, I tread water for three days in a row.
I woo women with my sensuous and god-like trombone playing. I can pilot bicycles up severe inclines with unflagging speed, and I cook Thirty-Minute Brownies in 20 minutes. I am an expert in stucco, a veteran in love and an outlaw in Peru.
Using only a hoe and a large glass of water, I once single-handedly defended a small village in the Amazon Basin from a horde of ferocious army ants. I play bluegrass cello…I am the subject of numerous documentaries. When I’m bored, I build large suspension bridges in my yard. I enjoy urban hang-gliding. On Wednesdays, after school, I repair electrical appliances free of charge.
I am an abstract artist, a concrete analyst, and a ruthless bookie. Critics worldwide swoon over my original line of corduroy evening wear. I don’t perspire, I am a private citizen, yet I receive fan mail…Last summer I toured New Jersey with a travelling centrifugal force demonstration…My deft floral arrangements have earned me fame in international botany circles. Children trust me.
I can hurl tennis rackets at small moving objects with deadly accuracy. I once read Paradise Lost, Moby Dick, and David Copperfield in one day and still had time to refurbish an entire dining room that evening. I have performed several covert operations for the CIA. I sleep once a week; when I do sleep, I sleep in a chair. While on vacation in Canada, I successfully negotiated with a group of terrorists who had seized a small bakery. The laws of physics do not apply to me.
I balance, I weave, I dodge, I frolic, and my bills are all paid. On weekends, to let off steam, I participate in full-contact origami. Years ago, I discovered the meaning of life but forgot to write it down. I have made extraordinary four-course meals using only a mouli and a toaster oven. I breed prize-winning clams. I have won bullfights in San Juan, cliff-diving competitions in Sri Lanka, and spelling bees at the Kremlin. I have played Hamlet, I have performed open heart surgery, and I have spoken with Elvis. But I have not yet gone to college.
I have never minded bringing up old threads. The information is still relevant. The complaints about old postings tells more about the complainers than the posting.
I have tried to remember, seems to me that my 2002 Sienna has seen nearly 11,000 feet, but that is by memory. When one drives on the high speed tollway from Mexico City toward Puebla, you start at 7200 feet, go way high, then drop back down to 7200 feet for Puebla, then at the east end of the state go back up to around 8200 feet, then in 17 miles drop to around 3000 feet.
But, as I said, that 10,500 or 11,000 is by memory and may not be correct. But, the old Sienna never showed any pain and it was definitely climbing hard. I have seen frost on that peak in the summer. It is not a rocky peak, but has pine trees and grass and normal stuff.
But. the poster is correct. You climb, you reach the peak, and then you go back down to 7200 feet again.
I mean, you’re not wrong in everything you said, but you were pretty bloody rude about it. No need to come on like a carload of turkeys.
BTW, you were entirely wrong with this one:
Cars tend to knock more when the mixture leans. What’s a lean mixture? That’s right. less fuel in the fuel-air mix. Your car can still put the same amount of gas in the cylinders no matter what the altitude is, so assuming the ECU doesn’t adjust the mixture appropriately, then if anything you will run rich, not lean, and therefore reduce pinging that may have already been present. Hence the reason why it’s OK to run 85 octane in Denver while you shouldn’t go below 87 in New Orleans.
My car always gets much better gas mileage at higher altitude. Going from 500 to 5000 nets me a 5 mpg increase in mileage at highway speed. I assume it must be lowered air resistance.
More like lowered fuel use. As the amount of air in the cylinder goes down, the computer automatically reduces the amount of fuel going into the cylinder. You end up burning less fuel as a result, hence better mileage.
By the same token, people often compensate for the reduced power by pressing further on the pedal to maintain speed.
Most of my altitude driving involves uneven terrain. Climbing steep grades followed by long downgrades coasting. If I’m gentle on the uphills, the coasting is icing on the cake.
Likely, the reduced consumption is a combination of all the factors mentioned.
Truth! I used to live near Sandia Peak in New Mexico. 10,500 feet up or so. We had an old Dodge Ram van with all of 95hp. By the time you got up to the peak you were flooring it just to maintain the 25mph speed limit.
Your post echoed the so-called “John Mongen Letter” which Tommy read on Cartalk maybe 2 decades ago. But your version seemed to have some different details if I’m remembering right. Either way, it’s hilarious and I’m glad to be reminded of it. Thanks for posting it!
I tend to get better gas mileage in uneven terrain, provided that the downhills aren’t too steep. The upgrades put your engine in its thermodynamic efficiency sweet spot and the extra energy you gave the car climbing the hill is returned on the downhill coasts.
Where you lose out in gas mileage is when the downhills are so steep that you end up throwing away the energy you burned gas to obtain during the climb because you have to ride the brakes to keep the speed in check.
Here’s an interesting article on the octane vs altitude topic. Denver gas apparently is a little lower in octane than the rest of the country by what the article says anyway.
I thought carbs compensated for air density in a similar way as fuel injection systems do, by effectively metering the air mass flowing down the venturi. If the air is less dense the venturi effect will product less vacuum, and less fuel will be sucked from the fuel bowl, so you end up with roughly the same fuel/air mix at high altitudes vs low. I know that some carbs had a kit you could install for high altitude use, so carbs probably don’t compensate as well, but it seems like they do compensate a little anyway. I used to drive my 2B carb’ed truck at 8-10K feet routinely when I lived in Colorado and never noticed much loss of engine performance at that altitude. I wasn’t drag racing at 10,000 feet of course, but for normal driving around not much difference, other than perhaps more of a tendency to overheat. At really high altitudes above 12,000 feet I would notice an engine power loss then.
Carbs compensate but not enough. If you cut airflow through a venturi in half by keeping the air density the same but reducing the velocity in half, you have 1/4 the vacuum but 1/4 the vacuum results in 1/2 the fuel flow through the metering circuit. Thus fuel flow tracks air flow quite well when airflow is reduced by lower rpm or more closed throttle.
If you have 1/2 the airflow by keeping the velocity the same but cutting air density in half, then you have 1/2 the vacuum and now instead of 1/2 the fuel being sucked through the jets, you have the square root of 1/2 fuel being sucked through the jets, or 70.7 percent.
50% of the air getting 70.7 percent of the fuel makes for a rich mixture.
It takes four times the head to push twice the fluid though an orifice because in order for two times the fluid to go through an orifice, it has to go through it twice as fast and that means you are giving the fluid four times the kinetic energy.
Pitot tubes used to give indicated air speed on airplanes have the same issue. A pitot tube air speed indicator that is calibrated to show true air speed at sea level will not indicate 1/2 true air speed at an altitude where the air density is 1/2 that of sea level air, it will indicate 70.7 percent of the true air speed at that altitude. This has the fortunate effect of keeping the airplane’s indicated stall speed nearly constant at all altitudes. If a plane has a fifty knot TAS (true air speed) at sea level, it will have a 70.7 knot TAS stall speed at an altitude where the air is half as dense, but the IAS (indicated air speed) will still be 50 knots.
That’s why air speed indicators are not corrected for altitude to indicate true air speed. The indicated air speed is more useful to the pilot.
Yeah, there’s that pesky issue of roasting your brakes to death if you get careless and wait too long to start controlling the descent. Roasting brake pads have a unique odor that lingers. Smelled it many times and knew I would see a car or truck off to the side or in the runaway lane ahead…
