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Old 07-05-2008, 10:48 AM   #99
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After reading Andy's ideas about an air speed indicator a couple of years ago, I installed one. It have found it quite interesting to see the difference between a headwind, tailwind, sidewind and no wind. I can't say it has saved me any fuel, because I run between 55 and 60 already, so I really can't slow down from that, practically speaking. But it does explain why one tank gets better mileage than another. It is just like the difference between driving in mountains vs the flats. By the way, I also have an inclinometer that helps alert me to the effects of that in advance, too.

Now, if I drove at a speed that would allow some slowing down in unfavorable conditions, then the air speed indicator would, indeed, allow economy adjustments.

Nevertheless, the air speed indicator was well worth the $120 investment to me, just like all the other instruments that keep me informed as to what's affecting my rig's safety and performance.

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Old 07-05-2008, 12:09 PM   #100
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with PICTURES and GRAPHS and hifalootin' explanations...

here are 2 more threads that COULD be rolled into this one...

for the sake of economy.

some smart stuff there on mixing 'air' and other combustibles...


all of the true things that i am about to tell you are shameless lies. l.b.j.

we are here on earth to fart around. don't let anybody tell you any different. k.v.
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Old 07-05-2008, 01:37 PM   #101
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Originally Posted by vswingfield View Post
Sorry, but exactly wrong. When the vacuum goes down, you are opening up the throttle. You are implying that you get your greatest economy with your vehicle floorboarded!
Sorry, but exactly right.

Originally Posted by vswingfield View Post
I gotta admit, "pumping loss" is a new one to me. I can see that there is some inherent loss of energy when pulling a vacuum, but still, the higher the vacuum the less fuel you burn, period.
"Pumping loss" is the technical term for the energy your engine exerts to pump the exhaust out, and draw air in. Air you saying that freeing up exhaust flow does nothing for fuel economy?

You've heard of "displacement on demand" and "mutli displacement system" right? They improve fuel economy because a four cylinder with the throttle wide open and no intake vacuum is more efficient than an eight cylinder with the throttle half closed and loads of vacuum.

The pumping loss is why putting taller gears in the rear end kills the fuel economy. Does the wind resistance magically increase when you put taller gears in? Ofcourse not. But the engine RPM does increase, so you need to close the throttle a little more to keep the mass air flow the same.

Originally Posted by vswingfield View Post
Also, not all diesels are "turbo" diesels. Old Detroit Diesels had a mechanical supercharger (the 6-71 supercharger became famous on 426 hemi drag racers in the 50s and 60s) and were two-stroke diesels. Some other diesels have no supercharging at all.
I'm well aware of the history of engine aspiration methods and application.
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Old 07-05-2008, 06:37 PM   #102
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I tow my 71 4200# Tradewind with a 99 F250 Triton, 2wd, auto transmission. I usually tow with the transmission in D and overdrive on. I will turn off overdrive for steep uphills. I get around 12mpg in the 60-65 range.

Given the recent posts about throttle and mpgs would I be any better off towing without overdrive or in drive 2?
Sail on silver girl. Sail on by. Your time has come to shine.
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Old 07-05-2008, 09:11 PM   #103
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Basically you want the highest gear you can get away with. With an automatic all you can do is give it the option of taking the higher gear, you can't force it into the higher gear. With some vehicles the automatic transmission has a full manual mode though.

Transmissions are getting more and more gears, six in the Chrysler Hemi with automatic, and seven or eight in luxury cars. This combined with throttle by wire lets the computer decide the most efficient combination of gear and throttle opening to give you the power you're requesting.

I'm no Dodge person, but Chrysler has really been leading the way in the Hemi with low fricton coatings on the piston skirts, and heat insulating coatings on the cylinder head and piston crown to improve efficiency. Combine with a six speed automatic and throttle by wire and you can't go wrong.
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Old 07-10-2008, 03:19 PM   #104

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Wink I'm Happy

Just got back from a trip thru the Adirondacks with the 06 Burb. 8.1L

4:10 diff., 75psi/tires...Ave 11.9 mpg/550 miles,toe/hall mode,Up-hill AND

Down, 15 mph. vertikel wind speed. Toeing the "Frantic Banana".

Whatever flotz your bote.

Stream Safe
AF #1

"Sticks & stones can break your bones...and hail will dent your Airstream"

So when is this..."old enough to know better" supposed to kick in?
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Old 07-23-2008, 08:19 PM   #105
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That Big a Difference

On my just-completed 1800 mile round trip on mostly flat land (TX-OK-MO), I ranged from 12.5 to 14.7 MPG. The difference between a standard 65 MPH and slowing down to 60 was amazing. I did use max pressure on all tires (35 TV, 65 TT). Somehow I couldn't convince myself 5 MPH made that much difference.

This compares to 9-10 MPG with the same TV and the SOB. I reckon A/S's claim of 15% better mileage is no exaggeration.

My medium-sized truck has a short tank (22 gal), so getting around 250 miles of range was a real bonus. Heck, I wish I'd bought an A/S three years ago!

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gas mileage, tow vehicles

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