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Originally Posted by Tahoe_Hybrid
7.3L is about 10-11MPG on average so 26.6 is incorrect... the best bet is to find a wreaked newer diesel that is a 4 banger.... most of those 4 banger are getting 30-35ish in pickups...
the top part of the gas tank is larger i burn 15 of 25.5 gallons before it hits the 1/2 mark on my tahoe
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Tell that to my fuel usage vs distance traveled. I know the fuel tanks aren't great for being consistent so that tank might be abnormally high, but not quite that much. The next tank ended up being around 16mpg, averaged together it's still 20mpg, double of what you state.
I don't drive the truck like I stole it, it's a stick, and it's got the highest geared axle it could come with stock, 3.55. The topper on it helps slightly with areo. My dad's is the same thing but 4.10 gearing, no topper, and he was getting 15mpg with a tuner and beating the snot out of it. Both trucks have stock sized tires, not 40in like a lot of people like to do.
Generally speaking, the physical shape of a fuel/gas tank is tapered in at the top, so it should hold less fuel at the top vs the bottom. However if you're using the fuel gauge, then it depends how the OE company designed the float in the tank. I've had vehicles that were very linear like my corolla, while my dad's Camry goes 80+ miles before coming off full. Tank mounted angle and a ton of factors effect the reading including the wiring, connectors etc. It's a resistive based reading.
Anyway, as I drive the truck more, the mpg I'm getting should average out and become more and more accurate. Ball park 20mpg is right in the range I see a lot of people claiming with similar gearing and similar speeds.
Remember, this isn't the 7.3 IDI engine, it's the power stroke. It injects the fuel at much higher pressure which makes it burn better, plus the computer has more control over timing and such. I've seen some claims that the IDI's can do alright, but that's with modifying timing and injection amounts (like tuning a carb).
Empty a 4 cylinder would give better mpg I'm sure, but make the whole vehicle weight 19k lbs and that 4 banger will have a heck of a time with hills. 7.3L isn't my first pick for engine size, there's no real happy medium in the diesel world for Ford's. A cummins swap could give better mpg, but the cost of another truck, doing the swap etc will likely far outweigh any fuel savings I'd have. No point in spending a $1 to save $0.01.
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Originally Posted by Isaac Zachary
10-11mg in a diesel sounds depressing seeing how there are a few getting up to 15mpg in V8 gasoline trucks of similar sizes. Not that there wouldn't be an advantage with the 4 banger.
I wonder if it would be advantageous to deactivate certain cylinders in a large diesel. The more the load the more effcient so maybe that would help. ?? I guess it depends on the type of injection system, whether it's a common rail or an injector pump, for an example.
With an injector pump, adding a few extremely high pressure 12V solenoid valves on certain injector lines and then routing that back into the fuel return would do the trick.
There may be problems with the turbo spooling correctly when running on just a few cylinders though. Maybe multiple staged turbos would do the trick. ??
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Cylinder deactivation would be a neat concept on a diesel. I wouldn't trust Ford's electronics to do a good job though if it was designed that way from the factory (like their gas 8-6-4 setups, people always seem to have problems with it). I suspect an cylinder not getting fuel for extended times might have excess wear, but I don't know how the oil circuits are in the 7.3L. Moving the "dead" cylinders around would offset that issue, but then it takes a fast computer to process which cylinders to kill and such.
Ironically, I had a through of what the 7.3L would be like as a 4 cyl. It would turn into a 3.65L. I saw a video of someone reworking an engine and claiming to recover enough heat out of the engine to not need a radiator. If I remember right, one of the engines he did was the 4.3L v6, but turned it into a 3 cylinder. The head was removed and I suspect a block off plate was added, not sure how the actual cylinder deactivation was done, might have removed the pistons, or maybe they were left in to keep balance. I can't seem to find the video or any pages about it now. I do remember one of the things he did with the heat was pre-heat the gas coming into the engine. If I remember right, the target was just below the boiling point, or maybe it was over the boiling point but under pressure where it didn't boil till sprayed into the cylinder. I figured it was more on the lines of conspiracy theory, but I don't think the guy was claiming super crazy numbers and he converted several engines.
Anyway, a 3.65L that was tuned a bit hotter than factory with a turbo that works well with it and intercooler might meet my needs for hauling and give good mpg while empty. Most 4 cyl engines seem to be half that size so it would probably have a nice vibration running too lol.