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Old 03-25-2008, 04:06 PM   #1
Rooster's82
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Fuel efficiency...what MPG do you get?

So, a few questions about fuel economy and the 73-87 chevy pickup.

What are you running (engine, tranny, gears, mods) and what are you getting for MPG?

How do you squeeze every last mile out of a tank?

If you could build a truck from the ground up what do you think would be the most fuel efficient setup?

(i have no clue what my MPG is at the moment, my speedo doesn't work right now...but it doesn't seem to be as bad as i thought it would be)
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Old 03-25-2008, 04:35 PM   #2
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Re: Fuel efficiency...what MPG do you get?

-383ci stroker (~450hp/475ft lbs)
-M21 4 speed
-3.42 gears, 28" tires

14-15 MPG (50/50 city/highway)

If I were building a truck from the ground up and wanted max fuel efficiency, I'd do a LS1/T56 swap.
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Old 03-25-2008, 05:02 PM   #3
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Re: Fuel efficiency...what MPG do you get?

well i have a 305 with a th350 recently rebuilt unknown gears and my truck gets about 5-7 mph in NYC the carb seems to be off so im going to go back to a non edelbrock carb
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Old 03-25-2008, 05:19 PM   #4
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Re: Fuel efficiency...what MPG do you get?

the rig- 86 C-10
350 V8, TH350 transmission, an old tired rochester carb
I drive about 80% city and 20% highway, when I do drive it
It has stock 3:08 rear gears, and for some reason it has 31x10.5x15 tires on a 2wd
The only mods I have are royal purple engine oil, no cat converter, flowmaster muffler, and a K&N air filter.
Last time I checked, I got 10mpg. I think it's due to the ineffiency of the carb, and the way I drive it.
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Old 03-25-2008, 05:26 PM   #5
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Re: Fuel efficiency...what MPG do you get?

1984 SWB
383 - around 400hp
Manual Valvebody TH400
2900 stall converter
3.73 gearsl/Detroit Locker
275-60-15's

8-10 mpg.

If all I wanted was fuel economy, I would do a 283 or 302 with a two-barrel Holley, 200R4, 3.08's, should be good for over 20 mpg on the highway...
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Old 03-25-2008, 06:05 PM   #6
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Re: Fuel efficiency...what MPG do you get?

350 300hp edlebroc 650
th350
373 gears

275/60-15 tire

6 to 7 mpg I would get about 12 if I keep my foot out of it
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Old 03-25-2008, 06:14 PM   #7
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Re: Fuel efficiency...what MPG do you get?

I averaged 15mpg on my last tank.
92 carbd 350 with a th350 and 3:08 rear. I drive it like an old man lol
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Old 03-25-2008, 06:16 PM   #8
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Re: Fuel efficiency...what MPG do you get?

8 if Im lucky, on a downhill slope, and the wind is on my tail end...

I pass everything BUT a gas station...
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Old 03-25-2008, 06:29 PM   #9
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Re: Fuel efficiency...what MPG do you get?

1981 K10 305/350 all stock. No muffler, VERY low gears (5.56 or lower), 235/75R15's.

It's about 400-500 pounds lighter than stock due to the rust.

I get between 6-10mpg on it depending on weather. I live out on the prairie so I get the full brunt of ANY wind flat in my face. Generally when I'm late getting to work so I've got my foot in it.

BTW, a block from my house I'm doing 65mph for the 10 miles to work, so pretty much all my driving is highway.
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Old 03-25-2008, 07:27 PM   #10
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Re: Fuel efficiency...what MPG do you get?

88 K5 blazer, stock 350 tbi, 700r4 tranny, unknown rear gears.
14 mpg hwy, 10 or 11 in town


75 C-10. 454, th350 - also unknown rear gears -- might get 9 or 10 at best

(i dont drive 'em much anymore, but the 14 hwy my k5 gets is not much worse than my new 5.4l F150)
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Old 03-25-2008, 10:01 PM   #11
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Re: Fuel efficiency...what MPG do you get?

11 MPG but i need some work on the carb.
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Old 03-26-2008, 01:30 AM   #12
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Re: Fuel efficiency...what MPG do you get?

I'd be lucky if I get near 12mpg.....but that's not the point of my truck. If I was worried about MPG, I'd be driving a 'Yota.....

I guess you could try to build a '73-up truck to get OK MPG, FI smallblock, tall gears, OD, etc....but the truck is still a BRICK......
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Old 03-26-2008, 03:04 AM   #13
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Re: Fuel efficiency...what MPG do you get?

89 454 TBI Burban, just did a 300 mile trip and got a solid 10 MPG thinking of putting a TB spacer, injector spacer and an adjustable fuel pressure reg on , supposed to help mileage.
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Old 03-26-2008, 03:24 AM   #14
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Re: Fuel efficiency...what MPG do you get?

87 Silverado swb 2wd
engine: high mileage 305 TBI
transmission: 700r4
tires: 265/75/15
gear ratio: not sure, but probably pretty high highway gears

I'm only getting about 12 mpg driving pretty easily. I'm a bit dissapointed since I thought the tbi would get a bit better mileage but it does have some pretty big tires, which I plan on dropping to a 255/70/15, and the motor is a bit tired.
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Old 03-26-2008, 03:35 AM   #15
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Re: Fuel efficiency...what MPG do you get?

Last time I posted BS started walking because some people don't think it's possible.

old stock 305 - 18 MPG at 70 MPG. Drove straight though the tanks too. Long 1000 mile trips.
305 - 13 MPG in the city. Lots of work on engine and truck.

ZZ4 - 13 MPG in the city so far. I can't seem to keep my foot out of it. 2500 stall and higher than normal shift points until the tranny is well broken in. I can't wait for a long trip out of town. I'm really curious on what it can pull off. Planning a trip in May. I'll drive through full tanks and calculate.
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Old 03-26-2008, 07:30 AM   #16
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Re: Fuel efficiency...what MPG do you get?

400- preformer II intake, 650 thunder carb, mild ( i mean mild RV cam crane i think), HEI, serp belt, hooker long tubes, flowmaster 50's with stock Y pipe and cat.
TH350C with Hurst shift kit. TQ is unknown stall
Stock open 10 bolt rear with the shatty 273's

On the high way i get about 12-15 MPG
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Old 03-26-2008, 11:22 AM   #17
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Re: Fuel efficiency...what MPG do you get?

After seeing and reading what I see here I guess I'm pretty lucky. I can understand Bob (Rusty) only getting 5 to 7 MPG in NYC on account it takes 3 days to cover that much ground, but the rest of you guys at 10 to 12?? Mine is an 84 K20 all stock. The engine has 465,000 miles on it and all I have ever done to it is rebuild the Q jet 4 times and do a valve job at 250,000. I did swap out the oil pan for a 5 qt and use the tall GM oil filters and really good oil (Mobile 1) Truck does ALL highway miles. Specs are 350 cid "M" eng 285 HP, Q jet carb, HD4 speed manual, 3:73 gears and tires are 235-85-R16 and a real light right foot. 15 to 17 MPG loaded or empty. jim 33 year GM mechanic
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Old 03-26-2008, 01:19 PM   #18
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Re: Fuel efficiency...what MPG do you get?

Bout 12 with a 454, t400 combo 4.56 gears and 33 x 12.5 tyres running straight propane, average driving conditions, hope to improve that with the addition of the gear vendors I have
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Old 03-26-2008, 06:29 PM   #19
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Re: Fuel efficiency...what MPG do you get?

I really need to get my speedo working. I feel like im getting over 12 but have no clue. i drive 12 miles to work each way, and i have made the trip 3 times plus errons and stuff over the weekend and im still on tank one with 1/4 left. So....about 100 miles on 12 gallons (16 gallons/.75)...12mpg?

PS. I cruz, no lead foot here, and the drive is on US 19 so the average speed is 45-60mph.
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Old 03-26-2008, 07:54 PM   #20
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Re: Fuel efficiency...what MPG do you get?

1980 3/4 ton, stock carbed 350 bored .030 over, turbo 350, 3.73 gear, I average 11 mpg no matter city or hwy, how fast or if I am pulling my camper I can always count on right around 11.
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Old 03-27-2008, 12:41 AM   #21
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Re: Fuel efficiency...what MPG do you get?

1975 C20 long bed with clamp shelf.
Engine 350 with a mild RV cam, TBI and custom real time tuning (highway lean cruise not enabled, yet)
Transmission 700R4 with stock converter (about 1400 RPM)
Rear end 4:10 with 33 inch tires

Highway about 17 mpg, city 13 mpg. Previously, before converting to EFI with Q-Jet i was getting 12 mpg on highway and 9 in city.

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Old 03-27-2008, 06:08 AM   #22
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Re: Fuel efficiency...what MPG do you get?

engine: reman 350 vortec w/headers, performer 600 cfm
tranny: reman TH350
rear: no idea
tires: 255/70-15

I get 15 with a pretty long freeway drive to work.
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Old 03-27-2008, 07:05 AM   #23
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Re: Fuel efficiency...what MPG do you get?

I get around 15mpg or so going 75mph...

78 c20, bone stock original 350, th400, 3.73 gears 265/75/16 tires.
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Old 03-27-2008, 10:59 PM   #24
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Re: Fuel efficiency...what MPG do you get?

82 Chevy c10- 350, th350, 3.08s and 32" tires.. about 8 city and not sure on highway... the high gears and big tires killed the around town mileage but the highway mileage was pretty good unless there was much of a head wind. With that tire/gear compo the torque just wasnt there.

87 GMC 2wd- tbi 305, 700r4, 3.08s and 235/75r15... about 16 around town. Which I thought was pretty good since my wife's 97 s10 blazer 4x4 got 16 as well.
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Old 03-28-2008, 09:01 AM   #25
Robert1970C20rstbukt
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Re: Fuel efficiency...what MPG do you get?

On the '86 crewcab, I don't wanna know! It's an off the road only truck at the moment.

'84 Chevy flatbed dually with around 60,000 original miles
454/SM465/4.10 D70 cab-chassis rear
I figure about what, 6? in town and MAYBE 10-11 highway? I hadn't driven it on the highway long enough to check. About a month ago I installed a high performance cap/rotor, then a set of Bosch 8MM wires and R45TS Delco plugs gapped at .045. Monday the timing(4 degrees before TDC) and carb were adjusted and she's running good!
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