View Poll Results: What's your highway mileage and fuel delivery system?
1 to 3 mpg 0 0%
4 to 6 mpg 0 0%
7 to 9 mpg 6 100.00%
10 to 12 mpg 0 0%
13+ 0 0%
Fuel Injection 2 33.33%
Carburetion 3 50.00%
Multiple Choice Poll. Voters: 6. You may not vote on this poll

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Old 04-23-2018, 12:34 AM   #1
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1966 26' Overlander
Houston , Texas
Join Date: Nov 2015
Posts: 6
Gas Mileage of the carbureted vs. fuel injected 454

Hi there,

I have a cousin who runs a small car dealership and has bought a few motorhomes over the years. He keeps them for awhile, fixes a few things, and then eventually sells them. He's not a motorhome dealer but he's driven and used perhaps a few more motorhomes than average. He was telling me that in his experience only that the fuel injected 454s (especially the Vortec 454) usually got about 12 MPG while the carbureted 454s got around 6 MPG on the highway.

Has this been everyone else's experience?
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Old 04-23-2018, 02:37 AM   #2
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1984 27' Airstream 270
Scotia , New York
Join Date: Oct 2012
Posts: 823
I doubt anyone has doubled their MPG in a change from carb to injection, unless the carb was in really bad shape.

I believe my 77 20 foot Argosy with the Qjet and headers "Could get" 10mpg.

My 84 27 foot Airstream came with a Qjet and it usually got about 6 to 8 mpg. I installed a TBI system and maybe I get 1 to 2 mpg better, but it is hard to tell. I dont drive enough miles, on the same route, carrying the same weight to get good numbers.


With the TBI, 12MPG in my rig would be unloaded, all down hill and a good tail wind


No matter what your fuel delivery method, weight plays a large factor in the final number.

If you are going to measure MPG, you cant use the gas gauge because it's accuracy is totally useless for that. You can fill to the top on each fuel stop, but that is a lot of weight to carry. I installed a dip stick in my tank and even parked on level grade, it is only accurate to 2 gallons out of 60, but better than nothing.


My next cheap method for better mileage is to try synthetic oil.
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Old 04-25-2018, 05:43 PM   #3
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1966 26' Overlander
Houston , Texas
Join Date: Nov 2015
Posts: 6
Quote:
Originally Posted by WayneG View Post
I doubt anyone has doubled their MPG in a change from carb to injection, unless the carb was in really bad shape.
I'm sure that's right. I don't think FI alone would make that change. Technically speaking the doubling mileage (in his experience) was from the 454 Vortec, which according to him is supposed to have different head designs in addition to fuel injection.

Quote:
Originally Posted by WayneG View Post
No matter what your fuel delivery method, weight plays a large factor in the final number.

If you are going to measure MPG, you cant use the gas gauge because it's accuracy is totally useless for that. You can fill to the top on each fuel stop, but that is a lot of weight to carry. I installed a dip stick in my tank and even parked on level grade, it is only accurate to 2 gallons out of 60, but better than nothing.
All good points. Thanks.
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Old 04-25-2018, 08:23 PM   #4
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Menomonee Falls , Wisconsin
Join Date: Jul 2010
Posts: 143
Hey,
I had 2 GMCs. One had a 455, the other had a 403. The 455 got 7 to 8 mpg.The 403 got around 10 mpg. My brother bought the 78 GMC from me. And claimed he got 13 one time. Point is, these old 454 s were basically from the 60s like 1966 I think. If you put aluminum heads on them, did some engine work internally, put on fuel injection, I suppose you might pull 10 to 12 out of these things. We re pulling a lot of weight and wind drag. I'm putting on a FiTech TBI unit. I'll be impressed if I can get 10 mpg out of it. One trip out west will almost pay for itself in gas savings. We ll see. In my experience, 62 mph is the break point for top mileage. My GMCs got there best mileage at that speed. The airstream is a little taller so that may be a factor. Angle of windsheilds on both units seem to be pretty close. My GMCs weighted 11 k loaded
Alignment played a huge factor in the GMCs. That tag axle could also present a milage drainer. I'm going to put my AS on my Aligner this spring to see if the tag is scrubbing. I'm going to bet it is. My years with Hunter engineering, showed me many senerios in alignments tag axles were notoriously out of any kind of normal alignment spec. Sorry, got off on a tangent. Anyway... We ll see if the FTech tbi system is as good as they claim. DJ
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Old 04-26-2018, 06:29 AM   #5
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1986 34.5' Airstream 345
Londonderry , New Hampshire
Join Date: Mar 2017
Posts: 71
I bought a NOS Zemco ZT4 driving computer that I am going to install in my 345.
It measures the MPG continuously as you drive. It should be good at combating
my heavy foot.

I have not completed my restoration project so I am not on the road yet. Has
anyone else installed one of these?
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Old 04-28-2018, 10:15 AM   #6
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Menomonee Falls , Wisconsin
Join Date: Jul 2010
Posts: 143
Hey.
We got that vacuum gauge in the dash. If you keep the vacuum as high as you can, while driving, that would be your optimum gas milage. The FiTech fuel injection I'm installing has an O2 sensor on the collector of the header,. That is where the precise metering of fuel comes from. I'd be curious to see if the later AS with TBI injection, got better milage than our QUadrjets carbs. 454s were never great on milage, but today we got so many things we can do to enhance the engines capabilities. Headers, mufflers, better heads, fuel injection, radial tires, better alignment capabilities. Overdrive transmissions.I would think we should be able to pull 12-14 out of these units. That's my goal. From my racing friends, they say the heads are where you get the most performance from. I may go that route in the future. But for now, 62 mph should be the sweet spot . I think 22-2400 rpm is the best rpm to run at. I hope that doesn't put me at 55 mph. I may getting old....er but 55 is just to slow for me. DJ
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