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#1 |
Registered User
Join Date: Mar 2017
Location: Gladewater, Tx
Posts: 35
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Rear Gear change for better mpg
I have a 63 C10 with a 250 inline 6 put in a 700r4. When I had the tranny swapped I was told I had a 2.73 rear end. I am currently getting 11mpg, and I don't ever expect to get great gas millage out of this truck, but I was told going to a lower gear would probably help. I'm mostly city driving with some hwy miles. Does anyone else have this kind of setup and any thoughts on a good rear end gear setup?
Last edited by BigRed63; 06-21-2017 at 09:20 AM. Reason: change title |
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#2 |
State of Confusion!
![]() ![]() Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 46,860
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Re: Rear Gear change for better mpg
Overdrive with a 2.73 isn't a great combo, when using the OD portion of tranny. Keep it in none OD for in town driving. Personally, I have never heard of a 2.73 in the pre 72 years, mostly just 3.08 or 3.73. My 82 had a 2.73 with a T350. I average 11-12 in town and 15 ish on the highway (65-75MPH)
a 3.73 with 700R4 is a good combo for Hiway. Your intown will remain about the same though, least in my experience. As you know, the 250 is not a gas mileage engine.
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#3 |
Registered User
Join Date: Mar 2017
Location: Gladewater, Tx
Posts: 35
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Re: Rear Gear change for better mpg
Sorry, should have specified. The PO put the rear end on from an 84 Silverado.
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#4 |
Never Ending Projects
Join Date: Jul 2006
Location: San Diego, CA
Posts: 3,836
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Re: Rear Gear change for better mpg
If you do have a 2.73 gear, you didn't need a 700R4. In OD you are totally lugging the engine, which will actually get worse mileage and is not good for the engine in general. With the .64 OD ratio in the trans, you should be at a 3.50 or 3.73 ratio.
Most older engines seem to like a cruise RPM in the 2200-2400 range, as they are most efficient there. What's your OD cruise RPM?
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. 1965 C10 Panel, ![]() 1968 Chevy C10, Long, Fleetside, Hot Rod Hauler http://67-72chevytrucks.com/vboard/s...d.php?t=313233 SOLD 1965 Chevy C10, Long, Fleetside, Hot Rod C10 http://67-72chevytrucks.com/vboard/s...d.php?t=415702 SOLD We were given two ears and one mouth for a reason... listen twice as much and speak half as often... |
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#5 |
Registered User
Join Date: Mar 2017
Location: Gladewater, Tx
Posts: 35
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Re: Rear Gear change for better mpg
Sorry for late response, was wanting to get an accurate reading before posting. OD cruise is only about 1700 and 2000 in D, this is why I'm wanting to change out my rear gears. Hopefully soon I'll get some estimates on how much it will cost.
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#6 |
Post Whore
![]() ![]() Join Date: May 2015
Location: Alabama
Posts: 14,636
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Re: Rear Gear change for better mpg
Agreed with above..2.73s and 700r4 is not the best choice..here's a rpm calculator tool that might help..http://www.csgnetwork.com/multirpmcalc.html
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#7 |
Registered User
Join Date: Sep 2006
Location: Louisiana
Posts: 374
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Re: Rear Gear change for better mpg
Big Red:
One question. With transmission and rear end both changed, are you sure your speedo and odometer are accurate? There are free apps for a smart phone or a GPS where you can compare your speedo to see if it is accurate. I would do that first before you conclude on your current mileage. Regards, Steve New Orleans |
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#8 |
60-66 Nut
![]() ![]() Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 23,247
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Re: Rear Gear change for better mpg
This is confusing....is that in D or OD?
I agree on a gear change to either 3.42's or 3.73's depending on tire size.
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#9 | |
Never Ending Projects
Join Date: Jul 2006
Location: San Diego, CA
Posts: 3,836
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Re: Rear Gear change for better mpg
Quote:
3.73's would be a good choice, if it was my money to spend. Actually at 2000 RPM's in drive, I would have left the transmission alone.
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. 1965 C10 Panel, ![]() 1968 Chevy C10, Long, Fleetside, Hot Rod Hauler http://67-72chevytrucks.com/vboard/s...d.php?t=313233 SOLD 1965 Chevy C10, Long, Fleetside, Hot Rod C10 http://67-72chevytrucks.com/vboard/s...d.php?t=415702 SOLD We were given two ears and one mouth for a reason... listen twice as much and speak half as often... |
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#10 |
Registered User
Join Date: Mar 2017
Location: Gladewater, Tx
Posts: 35
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Re: Rear Gear change for better mpg
This is my first project truck, still have a lot to learn, but the PO told me he thought it had a 3.73 rear end, this is why I chose the 700r4. I didn't realize it was any different until I swap the tranny and the transmission guy told me it was a 2.73
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#11 | |
Never Ending Projects
Join Date: Jul 2006
Location: San Diego, CA
Posts: 3,836
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Re: Rear Gear change for better mpg
Quote:
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. 1965 C10 Panel, ![]() 1968 Chevy C10, Long, Fleetside, Hot Rod Hauler http://67-72chevytrucks.com/vboard/s...d.php?t=313233 SOLD 1965 Chevy C10, Long, Fleetside, Hot Rod C10 http://67-72chevytrucks.com/vboard/s...d.php?t=415702 SOLD We were given two ears and one mouth for a reason... listen twice as much and speak half as often... |
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250 chevy, differential, differential swap, rear diff, transmission |
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