12 Mpg @ 75-80 Mph - The 1947 - Present Chevrolet & GMC Truck Message Board Network

dmsteele92831 · 08-08-2007, 03:30 PM

I just got my truck back last Friday and went on a 500 mile round trip. I averaged 12 MPG at 75-80 MPH almost the entire way. I think thats pretty good for a 350 with all the bolt-ons and a 2004R tranny. Does that sound about right? I'm sure if I dropped it down to 60 MPH I'd be around 14 or 15 MPG.... oh yeah I've got 31" tires on there too.

67ChevyRedneck · 08-08-2007, 03:34 PM

Sounds kinda low. What rear axle do you have and is your speedometer correct? Mine runs slower than whats shown.

I got 15 mpg on my last trip to charlotte going about 75 the whole way with a 700R4.

dmsteele92831 · 08-08-2007, 03:41 PM

Speedometers not hooked up, I just gauged the speed of traffic and am pretty sure I was at about 75-80 MPH. I did have a dirtbike in the back. I think my TV cable needs to be adjusted though (that's getting done tomorrow). Not sure on the rear axle, I'm pretty sure it's geared high.

fastom · 08-08-2007, 03:50 PM

I get 14 MPG from my 2005 Nissan Titan 4X4, engine is a 5.6

The best I've gotten in the truck is 15 1/2 going 55 on a 300 trip.

I don't expect our old trucks should get better than a modern computer controlled vehicle. A carburetor is not that efficient!

Pl4yboy · 08-08-2007, 03:48 PM

I drive 75-80mph about 30 miles 3-4 times a week, and I'm getting 11-12 with a TH400, 350 with some mild mods, and a 3.73.

67ChevyRedneck · 08-08-2007, 04:16 PM

^That's crappy! My 00 Z71 consistently gets 18+ on the highway unloaded, and that's going 75 mph.

Edit: I see you live in Cali, y'all have "watered down" crap gas out there. It's cut with so many things (like ethanol) to reduce pollution that ALL vehicles in Cali typically get lower fuel mileage than other parts of the county.

72 cheyenne pdx · 08-08-2007, 04:32 PM

I get about 12-13 gpm in my truck. I also have about another 500-600 lbs camper on my truck. I figure I would be getting 13-14 gpm without that camper.

1970bowtie · 08-08-2007, 04:39 PM

Quote:

Originally Posted by 72 cheyenne pdx

I get about 12-13 gpm in my truck. I also have about another 500-600 lbs camper on my truck. I figure I would be getting 13-14 gpm without that camper.

gpm= gallons per mile..lol

sb69chevy · 08-08-2007, 04:42 PM

cdowns · 08-08-2007, 04:41 PM

when i had my truck with350/300hp 2004R tranny 4:11 rear carrying heavy fleamarket loads on the open road 1200miles in a weekend over 80mph i always got at least 16mpg unless i had the AC on then it would drop to 14.5

dmsteele92831 · 08-08-2007, 05:11 PM

Damn, then that's really bad if you were getting 16 mpg. I'm sitting right around 300hp with my 350 too and I'm pretty positive my gearing is higher than 4:11

bad6772 · 08-08-2007, 05:58 PM

my 67 gets around 16 mpg .292/3speed with stock gears. my 72 gets around 10/12 mpg. 375 horse ZZ3/400 trans 4.56 gear. and i doesnt see 80 alot........well it sees it real fast

and then about 65 is max on the freeway runnning some high RPMs after 65....im going to change it to 3.73s or 355s

Longhorn Man · 08-08-2007, 06:13 PM

Cad 425/TH350/4.10 gears, one ton fleet side truck, just over 5000 pounds on the scales, 12.5 MPG at right about 70 MPH revvin 3100 RPMs.

BurnoutNova · 08-08-2007, 06:31 PM

last month i hauled my truck fully laoded w/ a fully loaded 20' car trailer to a swap meet and got 16 mpg. 71 k10, 3.07 gears and 32x11.50 tires about 65-70 mph

a kid i work with just rebiult the original q-jet for me at school, he told me the instructor and him set it up for gas mileage... i was pretty impressed

snj8198 · 08-08-2007, 07:07 PM

With my set up I've been pulling a consistent 13 mpg on the hwy running 70-75mph.

Warren · 08-08-2007, 07:26 PM

worked it out, when I drive I can see the needle move so dont want to know.

400 sml block and 410 rear, have a 700R gathering dues that would be better in the truck and when I marry rich opting for a six speed. Other than burnouts I am not an auto guy.

One day will check, for now do the long drives in the little car.

Warren

Huck · 08-08-2007, 09:22 PM

My 72 cheyenne with a new crate 350, HEI, Edelbrock carb===18-20mpg highway. When I put an Edlebrock intake on it, it dropped down 1-2 mpg. When I put in Hooker headers, I lost another 1-2mpg. When I went back to stock intake and ram horns, I regained my original mpg. It's all about torque and gearing. I had 307 rear posi gears.

dmsteele92831 · 08-08-2007, 10:17 PM

That makes sense then, I've got Doug Thorley Headers, an Edelbrock performer intake, mild cam, dual flowmaster 40's, and an edelbrock 600 cfm carb (the 1406). I'll gladly give up the extra 4-5 mpg for the added power though

08-08-2007, 03:30 PM	#1
dmsteele92831 Registered User Join Date: Oct 2006 Location: SoCal Posts: 191	12 Mpg @ 75-80 Mph I just got my truck back last Friday and went on a 500 mile round trip. I averaged 12 MPG at 75-80 MPH almost the entire way. I think thats pretty good for a 350 with all the bolt-ons and a 2004R tranny. Does that sound about right? I'm sure if I dropped it down to 60 MPH I'd be around 14 or 15 MPG.... oh yeah I've got 31" tires on there too. __________________ 1968 c10 Chevy 2005 Infiniti G35 2006 Subaru WRX STi Last edited by dmsteele92831; 08-08-2007 at 03:34 PM.

08-08-2007, 03:34 PM	#2
67ChevyRedneck Hittin E-Z Street on Mud Tires Join Date: Nov 2004 Location: Greenville, SC Posts: 23,090	Re: 12 Mpg @ 75-80 Mph Sounds kinda low. What rear axle do you have and is your speedometer correct? Mine runs slower than whats shown. I got 15 mpg on my last trip to charlotte going about 75 the whole way with a 700R4. __________________ Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride American Born, Country by the Grace of God 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications!

08-08-2007, 03:41 PM	#3
dmsteele92831 Registered User Join Date: Oct 2006 Location: SoCal Posts: 191	Re: 12 Mpg @ 75-80 Mph Speedometers not hooked up, I just gauged the speed of traffic and am pretty sure I was at about 75-80 MPH. I did have a dirtbike in the back. I think my TV cable needs to be adjusted though (that's getting done tomorrow). Not sure on the rear axle, I'm pretty sure it's geared high. __________________ 1968 c10 Chevy 2005 Infiniti G35 2006 Subaru WRX STi

08-08-2007, 03:50 PM	#4
fastom That's right, it's Copper!! Join Date: May 2007 Location: Bakersfield, Central California Posts: 558	Re: 12 Mpg @ 75-80 Mph I get 14 MPG from my 2005 Nissan Titan 4X4, engine is a 5.6 The best I've gotten in the truck is 15 1/2 going 55 on a 300 trip. I don't expect our old trucks should get better than a modern computer controlled vehicle. A carburetor is not that efficient! Last edited by fastom; 08-08-2007 at 09:57 PM.

08-08-2007, 03:48 PM	#5
Pl4yboy Freeeeee Mason... Join Date: Sep 2006 Location: McAlester, Oklahoma Posts: 320	Re: 12 Mpg @ 75-80 Mph I drive 75-80mph about 30 miles 3-4 times a week, and I'm getting 11-12 with a TH400, 350 with some mild mods, and a 3.73.

08-08-2007, 04:16 PM	#6
67ChevyRedneck Hittin E-Z Street on Mud Tires Join Date: Nov 2004 Location: Greenville, SC Posts: 23,090	Re: 12 Mpg @ 75-80 Mph ^That's crappy! My 00 Z71 consistently gets 18+ on the highway unloaded, and that's going 75 mph. Edit: I see you live in Cali, y'all have "watered down" crap gas out there. It's cut with so many things (like ethanol) to reduce pollution that ALL vehicles in Cali typically get lower fuel mileage than other parts of the county. __________________ Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride American Born, Country by the Grace of God 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! Last edited by 67ChevyRedneck; 08-08-2007 at 04:24 PM.

08-08-2007, 04:32 PM	#7
72 cheyenne pdx Registered User Join Date: Nov 2006 Location: Portland Posts: 382	Re: 12 Mpg @ 75-80 Mph I get about 12-13 gpm in my truck. I also have about another 500-600 lbs camper on my truck. I figure I would be getting 13-14 gpm without that camper.

08-08-2007, 04:42 PM	#9
sb69chevy Registered User Join Date: Oct 2006 Location: Springfield, MO Posts: 375	Re: 12 Mpg @ 75-80 Mph __________________ 1969 C/10 swb, 350, powerglide (daily driver) 2005 CRV (wife's ride)

08-08-2007, 04:41 PM	#10
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: 12 Mpg @ 75-80 Mph when i had my truck with350/300hp 2004R tranny 4:11 rear carrying heavy fleamarket loads on the open road 1200miles in a weekend over 80mph i always got at least 16mpg unless i had the AC on then it would drop to 14.5 __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

08-08-2007, 05:11 PM	#11
dmsteele92831 Registered User Join Date: Oct 2006 Location: SoCal Posts: 191	Re: 12 Mpg @ 75-80 Mph Damn, then that's really bad if you were getting 16 mpg. I'm sitting right around 300hp with my 350 too and I'm pretty positive my gearing is higher than 4:11 __________________ 1968 c10 Chevy 2005 Infiniti G35 2006 Subaru WRX STi

08-08-2007, 05:58 PM	#12
bad6772 Official Site Guitar Shredder Join Date: May 2006 Location: Oz Posts: 3,955	Re: 12 Mpg @ 75-80 Mph my 67 gets around 16 mpg .292/3speed with stock gears. my 72 gets around 10/12 mpg. 375 horse ZZ3/400 trans 4.56 gear. and i doesnt see 80 alot........well it sees it real fast and then about 65 is max on the freeway runnning some high RPMs after 65....im going to change it to 3.73s or 355s

08-08-2007, 06:13 PM	#13
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: 12 Mpg @ 75-80 Mph Cad 425/TH350/4.10 gears, one ton fleet side truck, just over 5000 pounds on the scales, 12.5 MPG at right about 70 MPH revvin 3100 RPMs.

08-08-2007, 06:31 PM	#14
BurnoutNova Registered User Join Date: Mar 2004 Location: CA Posts: 2,057	Re: 12 Mpg @ 75-80 Mph last month i hauled my truck fully laoded w/ a fully loaded 20' car trailer to a swap meet and got 16 mpg. 71 k10, 3.07 gears and 32x11.50 tires about 65-70 mph a kid i work with just rebiult the original q-jet for me at school, he told me the instructor and him set it up for gas mileage... i was pretty impressed

08-08-2007, 07:07 PM	#15
snj8198 Registered User Join Date: Feb 2007 Location: Star Valley, WY Posts: 2,038	Re: 12 Mpg @ 75-80 Mph With my set up I've been pulling a consistent 13 mpg on the hwy running 70-75mph. __________________ Steve 1971 GMC Longbox. Full Roller Stroker 489 w/ FiTech EFI, Chris Straub Cam/NV4500/205/D60/14B w. Grizzly Locker and 4.11's. 2" Lift on 33's

08-08-2007, 07:26 PM	#16
Warren Registered User Join Date: Dec 2006 Location: Ontario Posts: 73	I havent worked it out, when I drive I can see the needle move so dont want to know. 400 sml block and 410 rear, have a 700R gathering dues that would be better in the truck and when I marry rich opting for a six speed. Other than burnouts I am not an auto guy. One day will check, for now do the long drives in the little car. Warren



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08-08-2007, 09:22 PM	#17
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,261	Re: 12 Mpg @ 75-80 Mph My 72 cheyenne with a new crate 350, HEI, Edelbrock carb===18-20mpg highway. When I put an Edlebrock intake on it, it dropped down 1-2 mpg. When I put in Hooker headers, I lost another 1-2mpg. When I went back to stock intake and ram horns, I regained my original mpg. It's all about torque and gearing. I had 307 rear posi gears.

08-08-2007, 10:17 PM	#18
dmsteele92831 Registered User Join Date: Oct 2006 Location: SoCal Posts: 191	Re: 12 Mpg @ 75-80 Mph That makes sense then, I've got Doug Thorley Headers, an Edelbrock performer intake, mild cam, dual flowmaster 40's, and an edelbrock 600 cfm carb (the 1406). I'll gladly give up the extra 4-5 mpg for the added power though __________________ 1968 c10 Chevy 2005 Infiniti G35 2006 Subaru WRX STi

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