6.4 Bad Fuel Milage - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 9 (permalink) Old 03-20-2007, 06:52 PM Thread Starter
 
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Exclamation 6.4 Bad Fuel Milage

Don't know why everyone is crying about the fuel milage. Oh and its not going to increase 10mpg after breakin. Here is why:

First, go educate yourself about BSFC (break specific fuel consumption) on a diesel.
2nd- displacement. The more volume in the cylinders, the more fuel/air it requires for the same rpm.
3rd-Every body thinks the twin turbo is cool.......spools quicker right! that equals more air which requires more fuel- sooner.
4th- HP, takes fuel to make power, more power=more fuel (see number 1) Thats why everybody has to put bigger fuel pumps on when they start doing the high hp mods.
ReGen- wastes fuel
4.30/4.88 gears-aren't conducive to any thing but pulling. Unless some makes a trans with a quadrupple overdrive, milage WILL suck.

Moral of the story-if you can't afford the fuel bill, don't buy the truck. On average the 6.4 WILL NOT get better milage than a 6.0 in the same truck with the same final drive ratio. A 6.7 Cummins won't be better than a 5.9. The 05/06 cummins (325/610) IS less than an 03/04 (305/555) See number 4
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post #2 of 9 (permalink) Old 03-21-2007, 12:16 AM
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not to ask a dumb question hear. But wouldn't it seem that you should be able to get very similar mileage with (ex. 325hp as the 305hp) version as long as you keep your foot out of it? Yes i know it takes more fuel to make that extra hp but shouldn't fuel comsumption be about the same if you don't use that extra hp?

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post #3 of 9 (permalink) Old 03-21-2007, 12:38 AM Thread Starter
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If the programing on the higher hp motor was tuned to make the same or less hp/tq at cruise rpm or any same rpm minus the difference in volume..But as most diesels are programed to have power come on sooner (low rpm/high torque) not likely. Take a look at the hp/tq curves on the engines and then compare the fuel consumption on both and you shall see.

Because the engines are capable of so much power beyond stock, they should develop an inline 4 or 5 cylinder around 3 liter at 200hp and put it in a half ton. It would get over 30mpg
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post #4 of 9 (permalink) Old 03-21-2007, 01:13 AM Thread Starter
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http://marine.cummins.com/attachment...6B/fr91260.pdf

http://marine.cummins.com/attachment...6B/fr90208.pdf

Here are the charts, both for a 5.9 cummins 355 vs 315 hp even at idle, the higher hp uses more fuel.
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post #5 of 9 (permalink) Old 03-21-2007, 02:12 AM
 
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Good post to set expectations. I am surprised that my 6.4 is returning almost the same mileage as the 6.0. To your point about the available power under the curve; that is why the truck holds the gear when it's on an incline so much longer. No mystery though, more power equals more fuel/energy used.

The more I drive the 6.4 the more I like it. It's worth 1 or 2 MPG vs. a 6.0.
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post #6 of 9 (permalink) Old 03-21-2007, 09:22 PM
 
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Whats the deal my truck only holds 23.5 gallons. The two times I filled up with under 15mi till empty I have not filled over 23.5 gal. The window sticker claim the truck has a 30.5gal. tank. I need more than a 300mi range.:shrug:
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post #7 of 9 (permalink) Old 03-22-2007, 12:12 AM
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Quote:
Originally Posted by Rainman
Whats the deal my truck only holds 23.5 gallons. The two times I filled up with under 15mi till empty I have not filled over 23.5 gal. The window sticker claim the truck has a 30.5gal. tank. I need more than a 300mi range.:shrug:
Are you filling it up yourself or is it at a full service station. The pump will shut off when it senses the foam come up to the neck. If you do it yourself, once the auto nozzle stops let the foam settle a little and run the fuel nozzle slow to prevent too much foam built up. I usually get about 5-6 more gallons after it shuts off automatically.

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post #8 of 9 (permalink) Old 03-22-2007, 01:00 AM
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Quote:
Originally Posted by duckbill
Don't know why everyone is crying about the fuel milage. Oh and its not going to increase 10mpg after breakin. Here is why:

First, go educate yourself about BSFC (break specific fuel consumption) on a diesel.
2nd- displacement. The more volume in the cylinders, the more fuel/air it requires for the same rpm.
3rd-Every body thinks the twin turbo is cool.......spools quicker right! that equals more air which requires more fuel- sooner.
4th- HP, takes fuel to make power, more power=more fuel (see number 1) Thats why everybody has to put bigger fuel pumps on when they start doing the high hp mods.
ReGen- wastes fuel
4.30/4.88 gears-aren't conducive to any thing but pulling. Unless some makes a trans with a quadrupple overdrive, milage WILL suck.

Moral of the story-if you can't afford the fuel bill, don't buy the truck. On average the 6.4 WILL NOT get better milage than a 6.0 in the same truck with the same final drive ratio. A 6.7 Cummins won't be better than a 5.9. The 05/06 cummins (325/610) IS less than an 03/04 (305/555) See number 4

I would have bought one of the new 6.4's if they would have done the smart thing and introduced a 6 speed TQshift with it this year. IMO, it's the bare minimum for the 6.4L. A 7 speed manual would have been an improvement over the ZF6, too. That was dumb on Ford's part, they need another O/D gear. Couple that 5 speed auot with an unproven (in the real world) diesel and I just couldn't do it. I hope it all works out for Ford!
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post #9 of 9 (permalink) Old 03-22-2007, 01:11 AM
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Quote:
Originally Posted by Duke
I would have bought one of the new 6.4's if they would have done the smart thing and introduced a 6 speed TQshift with it this year. IMO, it's the bare minimum for the 6.4L. A 7 speed manual would have been an improvement over the ZF6, too. That was dumb on Ford's part, they need another O/D gear. Couple that 5 speed auot with an unproven (in the real world) diesel and I just couldn't do it. I hope it all works out for Ford!
I would've considered a 7speed:Thumbup:
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