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Rear end order option 8.8 or 9.75

Which rear end


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KBKEITH

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All I can say is that the 2.7/3.73 is a really nice combination if you’re interested in low end acceleration. Truck pulls like a mule from a dig.

My summertime highway MPG is in the 22.5 - 23.5 range. The best tank I had last summer was 23.8.

ETA: here is a calculator so you can get an idea of the difference in engine RPM at a given speed between the 3.55 and 3.73.

Engine RPM Calculator | Spicer Parts
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Mtnman1

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Thanks! And yeah the price is very similar. For the 2.7 you have to get the payload package to get 9.75, which is like $1k or something.
But yeah, my biggest concern with the 3.73 is whether the gearing and overall size will cause any noticeable impact on fuel economy. If not then this seems like the way to go.
Your driving style/habits have more effect on MPG than the rear diff.
 

Buyer2021

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@shawizkid I suggest you pay attention to the use-habits of those who advocate the lower-ratio / physically larger gearset and ask yourself if that's really comparable to your situation.

.... truck will be daily driver, hauling cargo in the bed from time to time, but rarely used for towing.
Given that use-profile, IMO you're a good candidate for the numerically lower ('taller') 3:55:1 ratio. Nothing about your described use-habits would stress the smaller gearset and related components, you might as well get the day-in-day-out long-term benefit of slightly better mileage for that daily driving.

Yes, your driving style likely has more effect on mileage, but unless you've a propensity for frequent jack-rabbit launches the lower ratio will yield better mileage all other things being equal (e.g. your driving style).

Nor does anything in your use-profile suggest that you would benefit from the payload package that's required for the 3:73, making that a rather expensive front-end cost for IMO no benefit for you. The payload package may have the side-effect of slightly harsher ride when empty or lightly loaded (which seems to be your typical situation); is that a characteristic you want for your daily driver?

Just for your consideration.
 
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shawizkid

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@shawizkid I suggest you pay attention to the use-habits of those who advocate the lower-ratio / physically larger gearset and ask yourself if that's really comparable to your situation.


Given that use-profile, IMO you're a good candidate for the numerically lower ('taller') 3:55:1 ratio. Nothing about your described use-habits would stress the smaller gearset and related components, you might as well get the day-in-day-out long-term benefit of slightly better mileage for that daily driving.

Yes, your driving style likely has more effect on mileage, but unless you've a propensity for frequent jack-rabbit launches the lower ratio will yield better mileage all other things being equal (e.g. your driving style).

Nor does anything in your use-profile suggest that you would benefit from the payload package that's required for the 3:73, making that a rather expensive front-end cost for IMO no benefit for you. The payload package may have the side-effect of slightly harsher ride when empty or lightly loaded (which seems to be your typical situation); is that a characteristic you want for your daily driver?

Just for your consideration.
Thanks for the input.
I agree on most accounts. Although my thought is if spending 55k on a truck, $700 extra for additional capability is probably worth it in case we were to buy a camper, which we’ve discussed previously.
Honestly if the 3.73 to 3.55 netted more than 1mpg, it might be worth it to go with the taller gear. But unfortunately I don’t think there’s enough reliable data to show how much of an impact between those gears.

ride quality isn’t really something I’d considered. But I’m guessing either are going be be better than my 2012 gmc 1500
 

Buyer2021

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.... in case we were to buy a camper, which we’ve discussed previously.
No worries, that's a different use-profile than stated in your original post; we can only make considered comments based on the info provided.
 

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amschind

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I voted for the 3.55, but that's not my favored option. The 5.0 NA engine with a 3.31 can pull well and get excellent mileage, but I wouldn't trade any of them for my Powerboost (which only comes with a 3.73).
 
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shawizkid

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I voted for the 3.55, but that's not my favored option. The 5.0 NA engine with a 3.31 can pull well and get excellent mileage, but I wouldn't trade any of them for my Powerboost (which only comes with a 3.73).
I have a 2.7 on order with the 3.73 9.75” rear. Even with that gear it’s final drive is taller with the 10 speed than a 3.55 and a 6 speed.

Glad to hear you’re enjoying your truck
 

tony72cutlass's'

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Honestly, I would be surprised if a final drive gear will make a crazy difference to your fuel mileage. Get what you like and give ‘er hell

The biggest contributor I can guarantee will be keeping your foot out of the go-juice pedal

if you’re not moving, gallons per mile = infinity

Ford F-150 Rear end order option 8.8 or 9.75 94-f150-monster-burnout-600
 
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konoplya

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is there a way to tell which rear i have, whether 8.8 or 9.75?
 

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fordtruckman2003

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is there a way to tell which rear i have, whether 8.8 or 9.75?
If you don't know your gear ratio you can get under truck and look. They are different designs with different bolt count.
 

amschind

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I would strongly recommend the 3.5 over the 2.7. The 2.7 is a great engine and overbuilt in most ways. HOWEVER, the oil pump is driven by a belt immersed in hot oil vs a chain or gears like every other engine out there. WHEN that belt fails, your engine will immediately die with almost zero warning.

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Atlee

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I voted for the 3.55, but that's not my favored option. The 5.0 NA engine with a 3.31 can pull well and get excellent mileage, but I wouldn't trade any of them for my Powerboost (which only comes with a 3.73).
4x2 PB's come with 3.55 rears. 4x4 PB's come with 3.73 rears.
 

tony72cutlass's'

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My vote is for 3.73 but NOT HD towing. I have abused my 3.73 standard 9.75 axle and it is an absolute beast.

Bonus points for axle nuts not coming adrift.
 

Samson16

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The 3.55 is the appropriate axle for this guys usage.
I voted before reading his post because that's the way the thread is layed out. Vote then find out why lol. 3.55 seems ideal for the 2.7 non-towing application.
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