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#51 |
Registered User
Join Date: Oct 2009
Location: Buhl, Idaho
Posts: 1,438
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Re: Fuel efficiency...what MPG do you get?
on my old 86 c30 crew cab dually (truck in my profile picture) had a 454/turbo400/3.73 gears with the quadrajet and a recent tuneup the best I saw was 12mpg, but the truck usually got around 7-8mpg.
![]() Truck went through lots of gas but it was worth it! ![]()
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86 c30 crew cab dually 454/400 4/6 drop SOLD 1-8-11 1981 chevy K10 short Bed Scottsdale SOLD 10-26-2020 67 GMC Stepside Straight six/3 on the tree "The Peach" 2020 Silverado Double Cab LT Z71 5.3 8 speed Daily Driver K10 build http://67-72chevytrucks.com/vboard/s...d.php?t=671934 The Peach build http://67-72chevytrucks.com/vboard/s...d.php?t=733903 ![]() |
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#52 |
Parts and more parts
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
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Re: Fuel efficiency...what MPG do you get?
City driving with mine does suck, but on the highway, I have spent enough time in getting the RPMs to a point where they are just about right. I still can put down 15 MPG and that is at 70 to 75 MPH.
My son's 86 does not do as well as mine and he has a 350 with a 700 R4 and the same rear end gears. It is all in the mix of each vehicle and how they are built.
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Frank Last edited by piecesparts; 01-16-2015 at 01:15 AM. |
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#53 |
Roadside Rebuilder
Join Date: Oct 2008
Location: Southeast Portland, OR
Posts: 421
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Re: Fuel efficiency...what MPG do you get?
'74 GMC 1/2 ton LWB, 2WD, 250-6, 3OTT, 3.73 rear end, Mighty Monojet (1bbl) with a recent rebuild, HEI, fully desmogged.
Highway, I get 17 if I keep it at 55. Have done as well as 20, but I was taking it super-easy on some relatively flat back-roads between Portland and Eugene. In town, I get about 15. I have no plans to change anything in my drivetrain. Would like to move up to a small 4bbl, or more likely, a 2bbl on a Clifford intake with a set of matching headers. Might be a small improvement in MPG, but mainly it'd just be more fun to cruise around in. I love a column-shifted manual, and prefer back-roads to the interstate. I live in Western Oregon, so I coast down all hills, and we have a lot of them. And I drive a semi for a living, so I'm used to taking my sweet time going uphill, which I do in my pickup too (within reason). If I have some long miles to go in a hurry, I'll take the family Corolla. Or more likely, I'll just leave a lot earlier and drive my truck. An empty road, a deep mug of hot coffee, dawn breaking over the mountains, and a happy inline-six warbling under the hood... Man, that's the only way to fly! |
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#54 |
Registered User
Join Date: May 2011
Location: Goliad, TX
Posts: 672
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Re: Fuel efficiency...what MPG do you get?
1990 Suburban 3/4 ton 4x4
25 mpg highway Cummins 6BT diesel Unfortunately, diesel is $1 more per gallon so there is little savings over a gas vehicle.
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1990 ¾ ton 4x4 Chevy Suburban -Cummins Diesel - 12 valve - factory rebuilt -6 speed bullet proof manual transmission - NV5600 -Gear Vendors Overdrive - HX35 Holset Turbo -NP205 iron transfer case -3.73 gears -2" Lift |
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#55 |
Registered User
Join Date: Oct 2014
Location: Spearfish South Dakota
Posts: 407
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Re: Fuel efficiency...what MPG do you get?
The other thing that happens is you dont have to fudge the# much to realy improve milage. Another guy and i got work trucks same time his got way better milage. No rounding up or down. 200 miles 10 gals 20mpg actual 190 miles 10.8 gals 17.5 mpg
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#56 |
Registered User
Join Date: Feb 2007
Location: Memphis MI
Posts: 1,851
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Re: Fuel efficiency...what MPG do you get?
81 3/4 ton 250 3OTT 3.42 16.5 8 ply snows, 17mpg at 45mph, 15 at 55.
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1987 2 ton ![]() 1982 ![]() Dad's 1981 ![]() Plus a mess o' tractors |
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#57 |
Registered User
Join Date: Jun 2009
Location: Oroville, CA
Posts: 4,827
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Re: Fuel efficiency...what MPG do you get?
'87 GMC SWB R10 4.3 tbi, 700R4 don't know the gears. I'm getting 18 mpg on the highway. It goes from zero to 60 in about 3 1/2 years!
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#58 |
Registered User
Join Date: Jul 2011
Location: back 40, bc
Posts: 3,817
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Re: Fuel efficiency...what MPG do you get?
lousy....
5 mpg's empty, around 3 with the camper & trailer on it... '85 K30 crew 454/T400/205, 4:56's 39" swamps |
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#59 | |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,484
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Re: Fuel efficiency...what MPG do you get?
Quote:
No numbers on my 82 C10 with 250 six, but will post some when I get the 355 installed. Should be pretty good with a mild GM roller cam, Vortec heads, and a 2.73 axle. Maybe 16-17 highway? I think the biggest problems with these trucks is wind resistance. And you can't tune that out or make up for it with taller gearing.
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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#60 | |
Roadside Rebuilder
Join Date: Oct 2008
Location: Southeast Portland, OR
Posts: 421
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Re: Fuel efficiency...what MPG do you get?
Quote:
I had a guy at work claiming his 14L Detroit was making 7 mpg over 900 miles. I pulled his fuel receipts and logs, and showed him how to do math with decimal points. Turns out he made 5.2 mpg... 7mpg in a 80,000 lb truck would be unheard of. If the numbers seem outlandish, they probably are. Last edited by Oregoon; 01-16-2015 at 03:28 PM. |
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#61 |
Registered User
Join Date: Jul 2011
Location: WV
Posts: 946
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Re: Fuel efficiency...what MPG do you get?
The 86 K10 I had, had a 305, 4 speed and 3.08's. Ran 32's on it and would regularly get 15.5 MPG.
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72 GMC C2500 402/Th400 first truck (still have) 77 GMC C3500 CC dually Sold ![]() 70 C50 dump truck "Rusty" 87 K10 Suburban Sold 93 K2500 xcab 6.5TD 96 GMC K2500 Suburban 6.5 TD |
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#62 |
Registered User
Join Date: Apr 2013
Location: New Mexico
Posts: 44
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Re: Fuel efficiency...what MPG do you get?
1990 1 Ton Crew Cab 4x4 Cummins 4" lift 34" tires with a heavy foot 22mpg
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#63 |
Just here to tinker
![]() Join Date: Jun 2008
Location: Holland, MI
Posts: 3,692
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Re: Fuel efficiency...what MPG do you get?
1978 1/2 ton with 5.7 diesel, T400, Gear Vendors overdrive, and 3:73 rear end yields me around 20 MPG on the highway and around 17 MPG in the city.
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78 C10 SWB Diesel #1 (wrecked)http://67-72chevytrucks.com/vboard/s...1978+silverado 78 C10 SWB Diesel #2 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=650751 60 GMC Suburban (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=445526 60 GMC 1000 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=298235 67 GMC 1500 (sold) http://67-72chevytrucks.com/vboard/s...d.php?t=803695 86 Suburban(summer unit) http://67-72chevytrucks.com/vboard/s...d.php?t=810697 88 Suburban 4x4(winter unit)https://67-72chevytrucks.com/vboard/...25#post8900725 |
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#64 |
Registered User
Join Date: Aug 2009
Location: S.C.
Posts: 1,593
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Re: Fuel efficiency...what MPG do you get?
Ok, I'll add mine. '73 included as I still owned it when this thread started.
--'73 K-20 Vortec headed 350, Summit 1103 cam, dual exhaust and headers. Stock size tires, no lift, 4.10 gears, turbo 350, np 205, plow gear installed, no dump, dump bed installed. 13mpg --'86 C-30 Stock 454, stock size tires, 4.10 gears,turbo 400, headers into factory duals. 11 mpg.
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'86 C-30 dually, 454/tbh400 '73 K-20 350/350/205 (sold ![]() I'm kinda like duct tape- no real purpose, but handy to have around. |
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#65 |
Parts and more parts
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
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Re: Fuel efficiency...what MPG do you get?
The tranny and rear end gear combinations is the whole trick to this. My Son's truck had 3.08 gears and when we put a 700 R4 in front, the mileage disappeared. The engine had to work too hard to keep up with the hills and traffic. We put a set of 3.73 gears behind the OD tranny and his mileage returned to a 14 to 15 MPG average.
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Frank |
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#66 | |
Roadside Rebuilder
Join Date: Oct 2008
Location: Southeast Portland, OR
Posts: 421
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Re: Fuel efficiency...what MPG do you get?
Quote:
![]() You can wring some damn good numbers out of damn near anything, Squares included. But, life is meant for living. Do it your way. I sure do! |
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#67 |
Registered User
Join Date: Dec 2012
Location: Preble county ohio
Posts: 1,914
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Re: Fuel efficiency...what MPG do you get?
mine got about 8 when i got it with the stock engine, i just rebuilt the engine with a small cam and a decent bump in compression, im hopeing for 11 or 12, the truck is a c30 crewcab,(like you dont already know!) with a 454/th400/3;73s,it has too short of tires on it right now, i am running 225/70/16, i believe they are 29" tall, i would like something 31" tall
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"DON'T TOUCH THE TRIM!!"-Early Kyler |
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#68 |
Registered User
Join Date: Aug 2011
Location: Tucson Arizona
Posts: 164
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Re: Fuel efficiency...what MPG do you get?
I've tracked my mileage very carefully over the last 65,000 miles and have averaged 12.01 MPG. About 65% highway driving, not necessarily expressway speed. I usually drive 65 on the x-way. Occasionally tow a boat or haul a 2000 lb camper which drops it down to 10 MPG but still figures in the overall average.
1985 GMC HD 3/4 4WD, stock 350, 790 cfm edelbrock, no overdrive, 3:73 gears, manual trans, dual exhaust, no headers. |
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#69 |
Registered User
Join Date: Nov 2014
Location: Alameda, CA
Posts: 877
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Re: Fuel efficiency...what MPG do you get?
790cfm carb on a stock 350? Why so large?
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1973 C20, 350/350 |
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#70 |
Registered User
Join Date: Aug 2011
Location: Tucson Arizona
Posts: 164
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Re: Fuel efficiency...what MPG do you get?
Sorry for the late response.
Had to replace the original Q-jet shortly after installing a new GM crate motor about 12 years ago. This was the recommended carb for that app. GM refers to this as an engine for commercial use (towing etc.). It has most of the torque at a fairly low rpm, seems to max out under 4000 rpm. Certainly doesn't bog so it's not overcarbed. Can't remember the original carb CFM but I believe it was similar to the Edelbrock. |
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#71 | |
Registered User
Join Date: Apr 2001
Location: DALLAS,TX
Posts: 21,964
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Re: Fuel efficiency...what MPG do you get?
Quote:
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67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... Cubic inches is like Indiana Jones with a cheap pistol. |
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#72 |
Registered User
Join Date: Jul 2012
Location: Winston, OR
Posts: 26
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Re: Fuel efficiency...what MPG do you get?
Shortbed lowered 2/4, 350 with Comp 280H cam, Edelbrock intake & 600 carb, headers-n-Flowmasters(2.5"), TH350, 3.43 gears, 29x12.50 tire= 13.3mpg mostly cruising around between 45-60mph..
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'59 Apache, short Fleetside, work in progress. |
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#73 |
Parts and more parts
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
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Re: Fuel efficiency...what MPG do you get?
I believe that your gear ratio and the 350 tranny is killing you. Your tires should be around 29" tall and when cruising at 60 MPH, you are at approximately 2300 to 2400 RPMs. That is not bad for the engine, but apparently you are missing the power curve somewhere. You may not be getting into the cam profile effectively.
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Frank |
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#74 |
Post Whore
![]() Join Date: Aug 2014
Location: Sacramento, CA
Posts: 10,827
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Re: Fuel efficiency...what MPG do you get?
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#75 |
Registered User
Join Date: Feb 2015
Location: Baltimore MD
Posts: 6
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Re: Fuel efficiency...what MPG do you get?
82 Long Bed 2wd
350 crate motor Edlebrock 600 carb and Edelbrock manifold Headman headers, Thrush Turbo mufflers 33x12.5 15 tires (old and brittle Mickey Thompson ATs) SM465 Trans gearing unknown (but probably stock as speedo says 45 when you are doing 65) Levelling/Lift kit (1 inch rear 3 inch front) Recently, I got around 10 mpg on a mostly highway miles tank (using MapQuest to determine actual miles covered), and driving 65 mph Switching to 235/75 15 Goodyear Wranglers this week as these weigh 33% less than existing tires and were a stock size for this truck. Thinking about removing the lift kit, as well, if it does not involve sourcing too many expensive suspension components. I would like to get 15 mpg on long highway drives down to North Carolina and up to New Hampshire for motorcycle rallies. Am I dreaming? This truck was a badly neglected old girl that I would like to bring back to good health and mostly stock condition and eventually pass along to my grandson. I have replaced the plugs, fluids, relocated a fuel line that was firmly hugging one of the right side header pipes (yikes!) and replaced the blown out glass pack mufflers. I drive like a grandpa. Even on the bikes. (Well, most of the time, anyway) |
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