Gear ratio change = how much better MPG - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 30 (permalink) Old 07-25-2007, 04:26 AM Thread Starter
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Gear ratio change = how much better MPG

Got a question about my trucks gearing. It's a 2wd cc dually with 4.10's and it will only get about 16 to 17 mpg highway, city whatever and 11 ish pulling my race car trailer.

I have been tossing around the idea of regearing to a 3.73 or 3.55
Tire size on the truck is the stock 215-85-16 so they are pretty short.

What could I expect for milage gains? What about towing...gain or loss in MPG?

How much pulling power will it loose while running along at 60 to 65 MPH towing a trailer?
I really hate it when you have to shift down for every little hill when towing, do you think that would be the case if I changed the gearing?

Eric
96 F-350 CC Dually
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post #2 of 30 (permalink) Old 07-25-2007, 05:31 AM
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Re: Gear ratio change = how much better MPG

keep the 4.10s, had 3.73 swapped in my fsuperduty from the 4.63 and the 3.73s sucked now went to 4.10s and love it

Joe "House" Kupferschmid
1995 F250 7.3 2.6 zf6 Puller
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post #3 of 30 (permalink) Old 07-25-2007, 05:17 PM
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Re: Gear ratio change = how much better MPG

Downshifting depends on the power.

I like the 4:10's in my buddie's 97 for towing ONLY, everything else it sucks and it's way too low.

Not sure what MPG you'd pick up. I'd say at least 1-2mpg at the same speed. It's nice to be able to run 70 at 2000rpms....
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post #4 of 30 (permalink) Old 07-25-2007, 06:10 PM Thread Starter
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Re: Gear ratio change = how much better MPG

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Originally Posted by gregrob View Post
Downshifting depends on the power.

I like the 4:10's in my buddie's 97 for towing ONLY, everything else it sucks and it's way too low.

Not sure what MPG you'd pick up. I'd say at least 1-2mpg at the same speed. It's nice to be able to run 70 at 2000rpms....
I kind of like them while towing up until I get on the interstate and run 75 to 80 MPH. That's approaching 3000 RPM on this beast and I'm sure milage will suffer. Guess I could just not go as fast like that will ever happen.

I have just been kicking the idea around of 3.73's but I will get a better idea of what I think of interstate towing in a month when I head to Boone, Iowa.
90% of the driving I do I don't run over 70 MPH, so maybe it aint even worth it.

Eric
96 F-350 CC Dually
300/100% B codes, Stealth dual pumps, H2E, BTS trans, ARP head studs, Comp 910 valve springs, Tyrant Tunes
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post #5 of 30 (permalink) Old 07-25-2007, 09:24 PM
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Re: Gear ratio change = how much better MPG

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90% of the driving I do I don't run over 70 MPH, so maybe it aint even worth it.
With a statement like that, it ain't worth it to gear swap.

However, it is sad to see that you drive like a granny all the time
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post #6 of 30 (permalink) Old 07-26-2007, 12:45 AM
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Re: Gear ratio change = how much better MPG

No doubt about it. Dropping the ratio will improve your MPG. Doing so (at the same road speed) cuts your engine RPM, thus your engine frictional HP.

I went from 3.73s to 3.08s and picked up 3 MPG in my mixed city/suburban (35%), Interstate (30%) state roads (35%) driving loop. Actually its my 42 mile one-way commute. Why did i go to 3.08s? because i couldn't find any 2.73s.

I don't tow much but when I do, its dense but not draggy loads (10,000 lb of shingles, 8,000 lb of machinery, and the occasional Bobcat). Pulling 10,000 lb of shingles through eastern KY (short steep hills) at night where I couldn't coast at all I got 15.5 MPG. My all time best was 29 MPG lightly loaded all Interstate.

One caution: If you have an automatic, I would not recommend going to less than 3.55. If you slow the engine down you also cut ATF flow through the cooler and a cooked tranny can result. I had a GMC with the wimpy 6.2 and a TH400 but added a Gear Vendor overdrive. That rascal went through transmissions like a teenager through potato chips. Five dead TH400s. spectacular failures - parts and oil scattered down the road. i never thought i'd see the day when something would kill a TH400 but the low end gruunt of even a wimpy dioesel will do just that.

With a manual, no problem.

I intend to much lower but I need someone who can custom-hob hypoid gears for my sterling 10.25.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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post #7 of 30 (permalink) Old 07-26-2007, 12:55 PM
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Re: Gear ratio change = how much better MPG

Quote:
I had a GMC with the wimpy 6.2 and a TH400 but added a Gear Vendor overdrive.
Dave, my parents had the same setup in a Chevy Suburban. Even without the Gear Vendor it was guaranteed that transmission would fall apart constantly. They replaced or rebuilt it every single year they owned it. Pretty sad really, that thing was a pig. But at least I know they weren't the only ones with the same problem.
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post #8 of 30 (permalink) Old 07-26-2007, 11:51 PM
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Re: Gear ratio change = how much better MPG

Pocket posted:
“But at least I know they weren't the only ones with the same problem.”

Dave says:
And the problem is/was by no means limited to GM. Ford automatics fail way too often. Dodge automatics fail way too often. Even the Allison 1000 behind high-revving Duramaxes fail way too often.

Manuals go through clutches at a variable rate depending on the driver. The NV4500 had the tail bearing nut problem but otherwise sticks are very reliable. That’s why even with arthritic football knees I want nothing to do with an expensive, frail, and inefficient automatic.

Racehauler posted:
“90% of the driving I do I don't run over 70 MPH, so maybe it aint even worth it.”

Dave says:
‘Tain’t so! By slowing down the engine at any road speed, you cut the engine frictional HP and thus reduce fuel burn

Hopefully, sometime this fall I intend to do some zero torque fuel burn tests in order to quantify fuel savings from reduced engine RPM. I have an AIC so I can set the engine to “idle” at any RPM I like. If I can put a couple of valves into my fuel system I can use a graduated container to measure fuel burn over a 10-15 minute period at a given zero torque RPM. To get a better feel I’d disconnect all the electrical loads possible so only the engine is in play. Get a figure for fuel burn at an “idle” at 1000, 1100, 1200 (a target RPM for me), 1300, etc up to about 2500 RPM. Then I can tell you how much fuel you are burning just to turn the thing over at a given RPM.

I need to find some new helpers. My old helpers got whacked with the useless stick and I don’t have Sapp’s talented hands myself.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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post #9 of 30 (permalink) Old 07-26-2007, 11:56 PM
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Re: Gear ratio change = how much better MPG

lol
Love reading your posts Dave
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post #10 of 30 (permalink) Old 07-27-2007, 02:05 AM
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Re: Gear ratio change = how much better MPG

maybe a gear venders overdrive..
you can keep your 4.10's and get lower gears when you need them.
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