Gas milage: 6cyl vs. 8cyl - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Piece of Work · 05-21-2009, 08:33 AM

What gas milage do you get with a 6 cyl, automatic? With a 8 cyl, automatic?

-Mark

big_al_71 · 05-21-2009, 08:37 AM

"406" automatic = 7-8 mpg

68gmsee · 05-21-2009, 08:46 AM

68 GMC six cylinder, 3 speed standard... 15-16 hwy
69 Chevy 350/350..... 14-16 hwy

Lemield · 05-21-2009, 04:19 PM

383 W/Th350 and GV overdrive: 15-16 on hiway....12-13 in town
454 W/Th400 : 9-11 MPG
Diesel VW: 44+ MPG combined city and hiway....done as well as 52 MPG once....sorry couldn't resist...

Ackattack · 05-21-2009, 05:37 PM

TPI 350/ 700R4/ 3.73 gears : 18mpg highway

Gray Ghost · 05-21-2009, 05:46 PM

Very little difference in the 6 and 8 mileage. You might see 3 mpg more with the six if you are careful.

Longhorn Man · 05-22-2009, 05:19 AM

the MPG listed here are not typical MPG of these trucks.

72BlckButy · 05-22-2009, 08:20 AM

With my I6 250/2spd powerglide, I have ranged from 12-21mpg, depending on my driving habits.

With my old '72, with a 400SB/TB350 I usually got 10mpg.

**WorkinLonghorn** · 05-22-2009, 09:07 AM

1963 C-10 LB 230 6 cyl, 3 on tree, 12MPG (work truck,lots of city traffic).
1969 2500 "longhorn" 350,4spd (truck type) 373 gears, 11-12 MPG(same roads)

Reno's71 · 05-22-2009, 11:06 AM

I was thinking that the 6 would get worse MPG because it needs to work harder to get the truck moving.

Botietruck · 05-22-2009, 07:34 PM

250 with 3 spd. manual & overdrive, with a/c on in the mountains & flat land = 16 mpg

red71c10 · 05-22-2009, 10:31 PM

Isn't it mostly about the rear end gears and not the engine transmission combo? My 1/2 ton gets close to twice the mileage my old 3/4 ton Camper Special got and they both had 350/350's.

67shortie · 05-23-2009, 05:14 AM

I run a 350 cid, aftermarket vortec heads, voodoo 262 equivalent cam, 10-1 compression, headers, performer intake, 1850 600 Holley with a dialed in HEI. The trans is a 700r4 with 3.42 rear gears.

I can't get better than 15 on the freeway, which I think is pretty decent considering. Now, add wind, higher than limit speed, traffic etc and it will dip down in the 12 range which is more common than 15 most of the time.

Around town, 10 is normal so I average 11-12 overall.

Never owned a 6cyl, so I have no comment on that engine

Brad · 05-27-2009, 08:30 AM

My old '67 with L6/T5/3.73 combo got a best of 18mpg with 150,000 miles on the clock. My current 350/350/3.08 gets a best of 13~14mpg with unknown miles, but it sure is fun!

big_al_71 · 05-27-2009, 08:38 AM

Some of these gas mileages are

UltraBlue71 · 05-27-2009, 10:24 AM

I gotta raise the flag too, I have heard of 15mpg plus 350 Chevrolets on the hiway, but I have yet to own one or witness it firsthand 12-13 mpg is it for these ole girls in stock form IMO. If you are doing better than that come by Idaho and give mine a tuneup please!

wHATANERD · 05-27-2009, 10:28 AM

my 69 350/400 combination 10.5 mph.

blakeaz33 · 05-27-2009, 10:34 AM

I get about 16 mpg combined city / hwy driving original 250 6cyl 3 spd with 3.73's.

69GMCLonghorn · 05-27-2009, 05:59 PM

It's all about those almighty RPM's! The more you get 'em down, the more MPG you're going to get (to a point, of course!). With 4.10's, I'm taching about 3050 at 70 MPH. I get a consistent 10 - 11 MPH with a somewhat built small block. it got 9 MPG bone stock, with choked up exhaust, Quadra-puke, and oil bath air cleaner. I've probably gained 75 HP and gained 10 - 20% in mileage; I have no complaints... wait, yes I do...

tim21391 · 05-27-2009, 06:27 PM

402 big block/auto.. i get about 4.. that is because im 18 years old and i have a heavy right foot..

ANTHONY67 · 05-27-2009, 08:20 PM

327 700r 373 17 hwy

UltraBlue71 · 05-28-2009, 02:00 PM

Quote:

Originally Posted by tim21391

402 big block/auto.. i get about 4.. that is because im 18 years old and i have a heavy right foot..

Holy Smokes, I knew 402's were bad, but damn! You must have a good job, or no bills, or both! Your dumping all that hard earned pay right into the tank, let off er son, let off er! Four Barrels are alot of fun tho!

69GMCLonghorn · 05-28-2009, 03:38 PM

Quote:

Originally Posted by tim21391

402 big block/auto.. i get about 4.. that is because im 18 years old and i have a heavy right foot..

When I was 18, I had my dad's '69 3/4 ton 307 4 BBL 4-speed. I floored it all the time too. The advantage was having that 307 instead of a big block, so I'd still get about 9 - 10 with my foot through the floor board.

Mayo · 05-28-2009, 03:43 PM

I got a 292 with a 5 speed and I get between 8-12 mpg

Blue71LWB · 05-28-2009, 04:47 PM

My inline 6 got 13.5 last time I checked. it was before I tweeked the carb , I'm hoping to have 15 in sight next time I check.

Manual trans.

05-21-2009, 08:33 AM	#1
Piece of Work Cultural Infidel Join Date: Jan 2007 Location: Clearwater, FL Posts: 668	Gas milage: 6cyl vs. 8cyl What gas milage do you get with a 6 cyl, automatic? With a 8 cyl, automatic? -Mark __________________ posted via La-Z-Boy -Mark 1972 C-10 Fleetside 350/TH350 PS PB A/C Cab Sadly....Sold 1968 Short Fleet 350/TH400 PS PB Delivered by Fine69 Also sadly Sold! It may be that your whole purpose in life is simply to serve as a warning to others. A man is not complete until he is married -- then he is finished.

05-21-2009, 08:37 AM	#2
big_al_71 Registered User Join Date: Jun 2008 Location: South Florida Posts: 11,375	Re: Gas milage: 6cyl vs. 8cyl "406" automatic = 7-8 mpg __________________ Get your facts first, and then you can distort them as much as you please!!!!!. Sylvester's build thread >>>http://67-72chevytrucks.com/vboard/s...ht=big+rebuild

05-21-2009, 08:46 AM	#3
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Gas milage: 6cyl vs. 8cyl 68 GMC six cylinder, 3 speed standard... 15-16 hwy 69 Chevy 350/350..... 14-16 hwy Last edited by 68gmsee; 05-21-2009 at 08:47 AM.

05-21-2009, 04:19 PM	#4
Lemield Registered User Join Date: Dec 2004 Location: Arvada Colorado Posts: 1,321	Re: Gas milage: 6cyl vs. 8cyl 383 W/Th350 and GV overdrive: 15-16 on hiway....12-13 in town 454 W/Th400 : 9-11 MPG Diesel VW: 44+ MPG combined city and hiway....done as well as 52 MPG once....sorry couldn't resist... __________________ Larry 1949 Willys CJ2A, Kubota Turbo Diesel engine, Warn Overdrive, 11 inch brakes, 12volt, Warn M8000 Winch "Little Green" 1970 Rustoleum Roller Red C20 Custom Camper 454 TH400 "Big Red" 1971 K20 6.2 Turbo Diesel 4x4 4spd Ranger Overdrive "Pumpkin Wagon" 2005 VW Beetle Diesel 44+ MPG "Silver Bullet"

05-21-2009, 05:37 PM	#5
Ackattack Senior Member Join Date: Aug 2002 Location: Valley Center KS Posts: 3,525	Re: Gas milage: 6cyl vs. 8cyl TPI 350/ 700R4/ 3.73 gears : 18mpg highway __________________ Project Bruiser: 68 Pro-Touring C-10 5.3L / 4L60E Project Ironhide: 97 GMC Crew Cab 4x4 Cummins SOLD: '69 GMC 1/2T SWB TBI'd: Project No Buck Assembly Manual Index Sign up Thread!!! Factory Service Manual Index

05-21-2009, 05:46 PM	#6
Gray Ghost Senior Member Join Date: Sep 2004 Location: Terrell, TX Posts: 1,967	Re: Gas milage: 6cyl vs. 8cyl Very little difference in the 6 and 8 mileage. You might see 3 mpg more with the six if you are careful. __________________ Kelly '05 GMC Sierra SLE Z71 Bone stock except for new bed rail caps.

05-22-2009, 05:19 AM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Gas milage: 6cyl vs. 8cyl the MPG listed here are not typical MPG of these trucks.

05-22-2009, 08:20 AM	#8
72BlckButy Tot Roddin' Join Date: Apr 2005 Location: Mid-MO Posts: 24,461	Re: Gas milage: 6cyl vs. 8cyl With my I6 250/2spd powerglide, I have ranged from 12-21mpg, depending on my driving habits. With my old '72, with a 400SB/TB350 I usually got 10mpg. __________________ -Nate 1969 CST SWB - Project Blank Slate (4.5/6" ECE Static Drop, 6-lug disc brake upgrade (manual), Billet Specialties Vintec 20x8.5 255/40 (F) 20x10 295/40 (R), 250 I-6) 1960 AMF Skylark - Tot Roddin' (Lowered with custom frame; soon to include custom push bar and interior) 2008 Silverado CrewCab 1LT (5.3L, 3:73, 4x4, LT1, Z-71, Towing Package)

05-22-2009, 09:07 AM	#9
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,873	Re: Gas milage: 6cyl vs. 8cyl 1963 C-10 LB 230 6 cyl, 3 on tree, 12MPG (work truck,lots of city traffic). 1969 2500 "longhorn" 350,4spd (truck type) 373 gears, 11-12 MPG(same roads) __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme.

05-22-2009, 11:06 AM	#10
Reno's71 Registered User Join Date: May 2009 Location: San Diego CA Posts: 47	Re: Gas milage: 6cyl vs. 8cyl I was thinking that the 6 would get worse MPG because it needs to work harder to get the truck moving.

05-22-2009, 07:34 PM	#11
Botietruck '71 chevy s.bed/s.side Join Date: Mar 2005 Location: Chesapeake, VA Posts: 1,571	Re: Gas milage: 6cyl vs. 8cyl 250 with 3 spd. manual & overdrive, with a/c on in the mountains & flat land = 16 mpg __________________ STILL PLAYS WITH CARS...AND TRUCKS!! Parents! Be good to your kids...they get to choose your nursing home! 250 I-6 with a 3 speed Saginaw and Borg Warner Overdrive...She's got overdrive!

05-22-2009, 10:31 PM	#12
red71c10 The Red Menace Join Date: Feb 2009 Location: Roseburg, OR Posts: 577	Re: Gas milage: 6cyl vs. 8cyl Isn't it mostly about the rear end gears and not the engine transmission combo? My 1/2 ton gets close to twice the mileage my old 3/4 ton Camper Special got and they both had 350/350's. __________________ 1971 Custom 10 - 350/350TH - Pwr steering, gauges, Chrome front bumper, Chrome hubcaps, Door edge guards, HD rear springs (current) 1968 C-20 Custom Camper - 350/350TH (orig 327), Pwr steering & brakes, gauges w/tach (former) 1968 C-20 - 307/3sp column (Dad's when I was a kid) "Driving is like coloring. Things get messy if you can't stay inside the lines."

05-23-2009, 05:14 AM	#13
67shortie Green club Join Date: May 2002 Location: Central CA Posts: 1,059	Re: Gas milage: 6cyl vs. 8cyl I run a 350 cid, aftermarket vortec heads, voodoo 262 equivalent cam, 10-1 compression, headers, performer intake, 1850 600 Holley with a dialed in HEI. The trans is a 700r4 with 3.42 rear gears. I can't get better than 15 on the freeway, which I think is pretty decent considering. Now, add wind, higher than limit speed, traffic etc and it will dip down in the 12 range which is more common than 15 most of the time. Around town, 10 is normal so I average 11-12 overall. Never owned a 6cyl, so I have no comment on that engine __________________ 71 short/fleet ECE 4/6 drop, LQ4/700r4/3.42 gears 70 SS396 Chevelle 427/200-4R/3.73posi 61 Lincoln Continental, black on black Son you are going to drive me to drinkin if you don't stop drivin that hot rod lincoln

05-27-2009, 08:30 AM	#14
Brad Out of the carpool lane. Join Date: Jan 2000 Location: Clark Co, WA Posts: 5,673	Re: Gas milage: 6cyl vs. 8cyl My old '67 with L6/T5/3.73 combo got a best of 18mpg with 150,000 miles on the clock. My current 350/350/3.08 gets a best of 13~14mpg with unknown miles, *but it sure is fun!* __________________ 1968 C-10 SWB, 5.7 Vortec/700R4/3.73 posi, Torch Red 1968 Camaro, 250/Powerglide, all original (No, I'm not gonna drop a 350 in it!...Jeez!) 2000 Honda VFR in the faster yellow! 2008 Husqvarna TE-610 1967 C-10 SWB 'Six Appeal'-Gone but not forgotten... Last edited by Brad; 05-27-2009 at 08:31 AM.

05-27-2009, 08:38 AM	#15
big_al_71 Registered User Join Date: Jun 2008 Location: South Florida Posts: 11,375	Re: Gas milage: 6cyl vs. 8cyl Some of these gas mileages are __________________ Get your facts first, and then you can distort them as much as you please!!!!!. Sylvester's build thread >>>http://67-72chevytrucks.com/vboard/s...ht=big+rebuild



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05-27-2009, 10:24 AM	#16
UltraBlue71 Registered User Join Date: Feb 2009 Location: OKC OK Posts: 489	Re: Gas milage: 6cyl vs. 8cyl I gotta raise the flag too, I have heard of 15mpg plus 350 Chevrolets on the hiway, but I have yet to own one or witness it firsthand 12-13 mpg is it for these ole girls in stock form IMO. If you are doing better than that come by Idaho and give mine a tuneup please! __________________ "You can put lipstick on a pig, sure it's pretty pig, but it's still just a PIG... 71 LWB Last edited by UltraBlue71; 05-27-2009 at 10:25 AM.

05-27-2009, 10:28 AM	#17
wHATANERD Registered User Join Date: Mar 2003 Location: Uvalde, Tx Posts: 407	Re: Gas milage: 6cyl vs. 8cyl my 69 350/400 combination 10.5 mph. __________________ 1969 C/10 Longbed undergoing rebuild. Old Chevy's Never Die, They Just Rust Around The Edges

05-27-2009, 10:34 AM	#18
blakeaz33 Registered User Join Date: Nov 2007 Location: Scottsdale, AZ Posts: 152	Re: Gas milage: 6cyl vs. 8cyl I get about 16 mpg combined city / hwy driving original 250 6cyl 3 spd with 3.73's.

05-27-2009, 05:59 PM	#19
69GMCLonghorn Registered User Join Date: Dec 2006 Location: Porter Ranch, CA Posts: 978	Re: Gas milage: 6cyl vs. 8cyl It's all about those almighty RPM's! The more you get 'em down, the more MPG you're going to get (to a point, of course!). With 4.10's, I'm taching about 3050 at 70 MPH. I get a consistent 10 - 11 MPH with a somewhat built small block. it got 9 MPG bone stock, with choked up exhaust, Quadra-puke, and oil bath air cleaner. I've probably gained 75 HP and gained 10 - 20% in mileage; I have no complaints... wait, yes I do...

05-27-2009, 06:27 PM	#20
tim21391 Registered User Join Date: Jul 2007 Location: Salina, Kansas Posts: 1,998	Re: Gas milage: 6cyl vs. 8cyl 402 big block/auto.. i get about 4.. that is because im 18 years old and i have a heavy right foot.. __________________ 1972 C-10...402/400..flowmaster 40 series 1967 Mustang 347 stroker/C-4 1966 Mustang 289/3-speed 2013 Mustang V6/6speed w/300 ponies I may be 23, but i sure do knows 67-72s are sexy! Its not MPG its smiles per gallon! build started 11/25/08 build thread: http://67-72chevytrucks.com/vboard/s....php?p=2993796

05-27-2009, 08:20 PM	#21
ANTHONY67 Registered User Join Date: Nov 2008 Location: FOREST MS Posts: 92	Re: Gas milage: 6cyl vs. 8cyl 327 700r 373 17 hwy

05-28-2009, 03:43 PM	#24
Mayo Cool Truck Join Date: Dec 2008 Location: Bowie,MD Posts: 1,869	Re: Gas milage: 6cyl vs. 8cyl I got a 292 with a 5 speed and I get between 8-12 mpg __________________ 1968 Chevrolet C20 Longhorn "Cool Truck" 1937 Chevrolet Pickup - Project Looking for a patina'd 68 50th Anniversary longbed

05-28-2009, 04:47 PM	#25
Blue71LWB Registered User Join Date: Nov 2006 Location: Alabama Posts: 120	Re: Gas milage: 6cyl vs. 8cyl My inline 6 got 13.5 last time I checked. it was before I tweeked the carb , I'm hoping to have 15 in sight next time I check. Manual trans. __________________ Working on my first 1,000 post. I'm sure I'll get there before this project is over .

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