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08-21-2017, 11:24 PM
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#1 |
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Registered User
Join Date: Jul 2014
Location: Alabama
Posts: 112
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Fuel mileage
I have been told that some people are getting around 20 mpg with small blocks with 700r4 trans and 342 or 373 gears . Are any of you guys getting that ?
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08-21-2017, 11:25 PM
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#2 | ||||
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"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,977
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Re: Fuel mileage
  Gary
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'cuz chicks dig scars... My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread. The Rebuild of Creeping Death after the wreck Quote:
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08-21-2017, 11:42 PM
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#3 |
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Account Suspended
 Join Date: Jul 2016
Location: Tacoma, WA
Posts: 6,873
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Re: Fuel mileage
The mileage they "say" they get and the actual measured mileage often varies....by a LOT
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08-22-2017, 12:22 AM
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#4 |
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Registered User
Join Date: May 2013
Location: Post Falls, ID
Posts: 901
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Re: Fuel mileage
327, 2jet carb, points, sm465, not sure of my gears.Non ethanol premium.
16 mpg highway. 60mph (steady) 12 mpg around town (depending how I drive) Smiles per gallon, LOTS 😀 |
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08-22-2017, 01:11 AM
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#5 |
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Registered User
Join Date: Jan 2001
Location: Orem, Utah
Posts: 7,998
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Re: Fuel mileage
20 MPG, downhill, with a tailwind and a light foot?
Still unlikely.
__________________
I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson |
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08-22-2017, 06:45 AM
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#6 |
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Registered User
 
Join Date: Feb 2013
Location: Spring Hill, Florida
Posts: 465
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Re: Fuel mileage
My math says that with my stock 350 with sm465 and well tuned 4 barrel (wide band o2) and 3.08 rear, I average 16 maybe 17 MPG. If I pop the secondaries I can watch the needle drop.
I will be dropping an NV4500 in shortly and will see what difference an OD makes. I have also been toying with going EFI so when i do I will see what i get... maybe with all of that 20 mpg would be possible, but I think I would rather a cam and head swap and pick up 50-100 hp instead. considering the cost of these mods if the goal is to save money on gas, it's a loosing fight. |
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08-22-2017, 07:59 AM
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#7 |
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Registered User
Join Date: Jul 2015
Location: 2nd left past the stump on a dirt road.
Posts: 2,629
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Re: Fuel mileage
I gave up on this one a long time ago, the amount of money to be spent to achieve this I might as well buy a new truck and try again
 I still want one of those carb fan thingys to spin when I lay on the pedal. |
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08-22-2017, 10:11 AM
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#8 |
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Registered User
Join Date: Oct 2005
Location: FL
Posts: 95
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Re: Fuel mileage
I have a 383 stroker with the R4 trans and I know for sure I am not getting 20mpg except when going down long hills.
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1972 C10 SWB, 1970 Corvette, 2017 Grand Sport |
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08-22-2017, 11:41 AM
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#9 |
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Registered User
Join Date: Feb 2014
Location: dallas area
Posts: 221
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Re: Fuel mileage
I get a solid 6-7 with a 402 and turbo 400 lol.
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08-22-2017, 11:54 AM
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#10 |
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Registered User
Join Date: Mar 2005
Location: 10-Uh-See
Posts: 5,609
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Re: Fuel mileage
My old stock 350 crate engine with TH350, 570 Holley carb, setup got around 12-15 with 3.73 gears, then got about 14-16 with the 3.07 gears.
You should expect somewhere between 14-18 with a 700R4, 3.42 or 3.73 gears and the proper carb.
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08-22-2017, 12:25 PM
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#11 |
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Registered User
Join Date: Oct 2016
Location: Dallas Texas
Posts: 3,267
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Re: Fuel mileage
My experience...
Recent: 2.80+/gallon... 402, 700r4, 3.73 in '67 C10 = less than 20MPG no matter how/where you drive it. Long Ago: 0.98+/gallon... 350, 350, 3.73 in a '68 C10 = way less than 20MPG at all times no matter what. Hth, -klb
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67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold |
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08-22-2017, 12:26 PM
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#12 | |
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Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,178
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Re: Fuel mileage
Quote:
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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08-22-2017, 01:18 PM
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#13 |
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Registered User
Join Date: Aug 2015
Location: Alcoa;Tn
Posts: 208
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Re: Fuel mileage
My best mpg with a 307,700r 3;08 rearend was17.6 driving so carefully blue haired old laides were giving me the finger! After that tankfull I never checked again.
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'71 Cheyenne Super LWB - Second Owner in 39 Years! '70 CST/10 SWB - Soon to be Daughter's truck when finished |
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08-22-2017, 01:50 PM
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#14 |
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Registered User
Join Date: Feb 2014
Location: dallas area
Posts: 221
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Re: Fuel mileage
Only c10 I've seen getting 20 had a lb7 duramax in it.
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08-22-2017, 02:40 PM
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#15 |
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Registered User
Join Date: Jul 2015
Location: 2nd left past the stump on a dirt road.
Posts: 2,629
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Re: Fuel mileage
I'm putting a call in to my cousin in North Dakota, those boys need to get back to work.
Turn the dam pump on fellas! |
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08-22-2017, 03:08 PM
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#16 |
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Who Changed This?
Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,790
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Re: Fuel mileage
I haven't checked around town, since it's pretty much start and stop. When I went camping in February, towing a 6000 Lb travel trailer on the freeway, on rolling hills, and some steep ones, not running the AC, I averaged 7 MPG. Still configured like in my sig. It used to get as high as 13 MPG on the highway with the old shell and no trailer. It's got over 100k miles since the rebuild, so it's gonna get it again soon. I'm not too worried about mileage- it's one of those vehicles that gets driven seldom, probably 3k miles a year. I considered an LS swap, but it will never pay for itself in my lifetime, in the fuel savings.
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~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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08-22-2017, 03:04 PM
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#17 |
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Registered User
Join Date: May 2016
Location: N/A
Posts: 55
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Re: Fuel mileage
I got 18 on a long interstate trip once with a 92 lt1 motor and 700r in my truck.
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08-22-2017, 03:39 PM
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#18 |
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Registered User
Join Date: Mar 2005
Location: Jurupa Valley, Ca
Posts: 1,211
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Re: Fuel mileage
70 3/4 ton 350 with th350 trans and 4.10 gears 9-11 city or hwy doesn't really matter. I find it hard to believe it would double with an OD unit. My guess is maybe 14-15 on the hwy.
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Terry 1970 Custom Camper/C20 , GM Crate 350/7004R, Dana 60, factory AC |
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08-22-2017, 06:39 PM
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#19 |
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Special Order
  
Join Date: Nov 2004
Location: Mt Airy, MD
Posts: 85,851
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Re: Fuel mileage
Why would GM come out with 6.2 diesels if 350s could get 20 mpg?
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ |
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08-22-2017, 06:54 PM
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#20 | |
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Who Changed This?
Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,790
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Re: Fuel mileage
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j/k The real reason is that a diesel has a ton more torque for the same displacement. The higher compression ratio allows a slower burning fuel, so they get better mileage, to boot. It's a win-win. I'd use one, but got sensitized to diesel fumes after years of working on them, and have to make sure I'm not following one, ever. The newer ones using DEF are better, though.
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~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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08-22-2017, 09:49 PM
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#21 | |
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Rottenwood Garage Member
Join Date: May 2005
Location: Marietta, Georgia
Posts: 4,321
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Re: Fuel mileage
Quote:
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2004 Chevrolet Suburban C1500 2001 Chevrolet 2500HD Crew 6.0 1999 Harley Davidson Electra Glide 1972 Chevrolet C-20 Custom Camper "Dump Truck" 1972 Chevrolet C-20 Suburban "Big Green" 1969 Chevrolet C-50 Wedge Hauler "Leonidis" 1966 C-10 2x4 short fleet 327 4 speed "Race Truck" 1952 Plymouth Cranbrook "Rican" (my grandfathers) 1931 Ford Model A Coupe "Black Beauty" 1930 Ford Model A truck "Club Cab" 4x4 Rottenwood Garage and Speed Shop.....where everything must be racy! It's not just a hobby..It's a LIFESTYLE!!! Thanks for nothing Barrett-Jackson You cant fix stupid or teach accountability! Time wasters, looky Lous and tire kickers are everywhere! |
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08-22-2017, 09:52 PM
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#22 |
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Rottenwood Garage Member
Join Date: May 2005
Location: Marietta, Georgia
Posts: 4,321
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Re: Fuel mileage
I have said it for years......if gas mileage is a concern, buy a Honda. I have never had any SBC that did better than 18 with a carb or injection.
__________________
2004 Chevrolet Suburban C1500 2001 Chevrolet 2500HD Crew 6.0 1999 Harley Davidson Electra Glide 1972 Chevrolet C-20 Custom Camper "Dump Truck" 1972 Chevrolet C-20 Suburban "Big Green" 1969 Chevrolet C-50 Wedge Hauler "Leonidis" 1966 C-10 2x4 short fleet 327 4 speed "Race Truck" 1952 Plymouth Cranbrook "Rican" (my grandfathers) 1931 Ford Model A Coupe "Black Beauty" 1930 Ford Model A truck "Club Cab" 4x4 Rottenwood Garage and Speed Shop.....where everything must be racy! It's not just a hobby..It's a LIFESTYLE!!! Thanks for nothing Barrett-Jackson You cant fix stupid or teach accountability! Time wasters, looky Lous and tire kickers are everywhere! |
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08-25-2017, 03:49 PM
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#23 |
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Registered User
Join Date: Dec 2007
Location: Southern CA
Posts: 210
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Re: Fuel mileage
Real world 5.3, 4l60, 3.73 with 32.5" tires. 45k overall average 17 mpg. Best was 22 mpg with a tail wind flat land cruise at 65. Worst was during the autocross I won
 .16 gallon fuel tank and low fuel warning comes on at @280 miles. I have 50-80 miles at that point.
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71 C-20 Custom Camper California Truck |
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08-22-2017, 08:44 PM
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#24 |
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Registered User
Join Date: Aug 2010
Location: central oregon
Posts: 160
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Re: Fuel mileage
hi guys, 70 lwb gmc. 350/ 350 3.07 rear, camper shell. 4500# 10067353 crate engine, performer, q-jet ,204-214 420 442 cam. best ever on freeway 14 mpg. in town, who knows, lol maybe 8 mpg.
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08-22-2017, 08:58 PM
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#25 |
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Registered User
Join Date: Mar 2016
Location: hickory, ky
Posts: 1,318
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Re: Fuel mileage
Stock 4 bbl 350 /3ott/ open 3:73 rear. 15 highway @ 55-60 mph all day long
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