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Old 07-31-2002, 12:19 PM   #1
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Who Wins Bragging Rights on MPG?

What is the BEST Miles Per Gallon rate that you can achieve with your stock, semi-modified, or fully modified Motor Home?

With low restriction and/or swirled intake systems; hot spark systems with multiple electrode plugs; tuned headers; oversize dual exhaust, or even quad exhaust; larger radials with higher air pressures and dual tires replaced with the larger single wheel and tires; tuned suspensions, air-lift shocks and careful loading to insure a slight forward rake to the coach; cruise control, ACs running on generators; constant value mpg read-out gauges; and the natural streamlining of AirStream Motor Homes...

On our old Vogue 43' with less streamlining than an AS but with everything else done correctly; we were able to achieve 25 years ago 15 mpg at 50 mph under ideal conditions which was I-95 from south of Boston to Norfolk in the cool fall season in the very early hours of Sunday morning when there was no traffic. This is all flat land and the humidity as well as temp were about 40. THE REST OF THE STORY, as Paul Harvey would say is: at 55 it dropped to about 13 mpg and at 60 mph it dropped to about 9 or 10 mpg and at 70 mph the mpg dropped to about 8 or less mpg. And, when trying to pass and flooring that big engine the mpg indicator would drop to 1 or 2 mpg!!!! Those ones and twos don't average in very well.


Who is getting the best gas mileage over let's say a 100 mile approximate distance or more; this would be BEST on flat land of course and probably at night in cool weather:

Here are the categories as I see them:

50 mph is anyone getting OVER 20 mpg?
55 mph >>> is anyone achieving 20 mpg?
60 mph >>> Here is where the AS streamlining really comes in
65 mph >>> is there anyone over 15 mpg?

70 mph >>> the REAL slow lane speed on many Interstates and this is where I think we SHOULD be able to beat 15 MPG by using all we know and doing it all correctly...

OK folks: HOW WELL CAN YOU DO???
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Old 08-03-2002, 11:00 PM   #2
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You can tune the engine all you want but you also need to consider the transmission. The newer units (90's) have a 4 speed OD transmission that gives them a big advantage of the late 70's and 80's models with trannys geared for the earth saving speed of 55mph. Going 60-70mph only increases your RPM's and decreases fuel economy. My 85 345 has the standard 3 speed transmission. I think 55-60 is my best RPM to speed ratio. Today's motorhomes are geared to cruise with low RPM's at 65-75mph.

The best options seem to be Banks, Jacobs, mid-grade gas, and to go easy on the pedal.
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Old 08-04-2002, 07:59 AM   #3
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I have the Banks system and the gas....but what's the Jacob's? I once figured my mile per gallon to be around 8? I about fell over.

And that was highway driving.....miscalculation or for real?
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Old 08-04-2002, 02:13 PM   #4
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I also go about 55-60 and it seems to be the "sweet spot" for my rig. I got about 9mpg on my last trip, in 90 degree weather and uphill and all that.
I expect that in the fall with cooler less humid days i might eek out 10, with generator off, and a flat road. But I won't be driving much over 60 anytime soon. I once did 65 on the way home from Mystic last April, on flat Alabama roads- and not for long.
By the way the Jacobs is the electronic ignition system that Peter and many others have ( or want to) . It has an uphill unit especially for Rv's.
check out their site at www.Jacobselectronics.com
they also have ceramic spark plug wires.
I also would like to know how to tilt my rig up in the back.. no actually I would like to know how to increase the rear ground clearance some, so my bikes don't drag going up to a hill from another road. Any way short of new, or more springs?
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Old 08-04-2002, 02:44 PM   #5
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Alan,
the airbags control your height. Remember how high mine were set?
This is how I solved the bike rack issue:
cut'n weld.
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Old 08-04-2002, 05:35 PM   #6
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Hi Alan,

Humidity actually enhances mileage. I just don't know if temperature has anything to do with it.
A certain amount of water content in the mixture makes the combustion process more efficient.
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Old 08-04-2002, 08:17 PM   #7
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Jacobs Ignition

I called Jacobs and talked with them, when I heard the price I decided to go another way. Then the guy said that they had some they pulled from production and checked as part of quality control, it was $100 less than the regular price. You might have to call a few times because I don't think it is a daily thing, but would be worth the time.

John
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Old 08-04-2002, 09:12 PM   #8
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My 28 ' gets 8 mpg most of the time I still have the stock ignition.I do have dual pipes though on the way back from newport oregon (the coast) this weekend we got 10.5 that is the best that we have done so far.we have done this once before but its not all that comon for us .On the way to the coast we got 8mpg but we ran the gen with the roof and dash air on and alot more hill climbing.the sweet spot seems to be 65 mph I'm not sure if its because its a little smaller than the 31s or what.Ive heard the banks system is the way to go.I still need to do the economy upgrades.
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Old 08-04-2002, 09:38 PM   #9
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I IMAGINE that the AS MotorHomes are more aerodynamic than our old Vogue was, although it did have a little bit of a sloped front end.

However, the difference in gas mileage from 45 to 50 and from 50 to 55 and 55 to 60 was in each case LARGE. I realized why the military convoys were designed to go 45 mph as a gas consumption control.

If any of you have a constant flow mpg gauge; give it a try for a few dozen miles at different speeds and check your mileage. It could well be that the streamlining of the AS makes 55-65 a sweetspot but I wonder if the mpg wouldn't be far greater at 50.

Nevertheless, for most people, I imagine, the mpg is not nearly as important as getting there quickly. Perhaps I enjoy the challenge of engineering efficiencies a little TOOOOOO much...
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Old 08-04-2002, 09:41 PM   #10
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Oh, and Ewe, yes the humidity and in fact water injection are able to give extra energy to the engine. The water converts to steam and boosts the HP and torgue to some extent.

Some of us old back-yard mechanics used to put water injection systems on our drag racers or road racers; and it was just some water jets which pumped small ammounts of water spray into the throat of the carb; you could FEEL it when you hit the water injection switch at mid-range rpms.
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Old 08-04-2002, 09:48 PM   #11
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John,
did you go with the Jacobs. If so, I would be interested to know your choice of plug gap.
I set mine to .055 - .060 and I am very pleased with the results.
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Old 08-04-2002, 10:06 PM   #12
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Jacobs

When I ordered it I never thought about gap, when Installing and looking at the coil I began to wonder. Called them back and they said .055. Runs great, plugs stay nice and clean. They are great to deal with, my fuel injection and ignition are all hybrid, spent about 20 minutes with me explaining how their system worked so I could make it work with mine. Probably some of the best people I have dealt with since starting this.

John
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Old 08-04-2002, 10:23 PM   #13
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John, with your 24' lenght, you must have a hot rod.
The Jacobs people are proud of their product and stand behind it. Did yours come with the small uphill/downhill module?
I was amazed at the performance enhancement on my 454. I can easily climb steep hills @ 40- 45 mph even passing slower cars. And you are right about the nice looking plugs.
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Old 08-04-2002, 10:33 PM   #14
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Jacobs

Just the coil and controller, and a 'valet switch.' Nice feature, but confused me at first. Has to be grounded and I couldn't figure why it would run and die. Had so many wires from so many different directions, kept checking everything, low oil pressure shutdown, fuel pump, ecm power, etc. Finally thought about that and have been OK since.

John
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