12 mpg Help!! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

OrangeAnimal · 05-10-2009, 05:52 PM

I drove my truck this weekend to houston and back. About 220 miles round trip. Burned almost 2 tanks of gas. 16 gallon tank. The engine is pretty much stock. 350 4 bolt main, RV cam (wish I had specs) Flat top pistons, 1.94/1.50 valves stock heads. Edelbrock Performer EPS intake, Edlebrock Performer Carb. Timing is set base 8*, Vacuum Advance hooked to full vacuum limited to 14* at idle, My full mechanical timing is 32* My full vacuum timing no load is 42* degrees. I spent alot of time working on it and have not gotten the mileage any better. My rear end is a 3.07 open diff. I am lowered 5/7 running 20's with a 28 inch total tire diameter. At 65 mph I am running 2300 rpm could this be the culprit? I didn't think is was too high rpm.

I Figured this thing would get better mileage than this. I could be wrong though. I guess it could be a jetting issue as well. It's a 1406 carb. Anyone have a good starting point for the jetting or should I ditch this for the Fuel injection if I am looking for mileage? I also noticed one other issue. It is too rich once it's warmed up good floods easy when try to start it. I hadn't ever had this problem b4 the trip to Houston. Any thoughts or ideas would be great.

3r!c84 · 05-10-2009, 05:59 PM

i have the same thing on my truck and its all stock,with the 305 and th350 and im runing the stock tire size,stock gearing.
when i went to daytona i got 12.7 -13 mpg? and i was only going 60-65mph

OrangeAnimal · 05-10-2009, 06:11 PM

Well crap thats no good. I am sure that these trucks got better highway mpg than that.

3r!c84 · 05-10-2009, 06:16 PM

yea but with no O/D they rev high going down the highway
idk about the trucks with the 700r4's

look at this

http://www.73-87.com/7387info/ads_GM/82_20mpg.jpg

you know the guys at GM where lieing lol

pokethesmot · 05-10-2009, 06:17 PM

i have a sbc 400 and thats about what i get

Manbearpig · 05-10-2009, 06:33 PM

Quote:

Originally Posted by 3r!c84

look at this

http://www.73-87.com/7387info/ads_GM/82_20mpg.jpg

you know the guys at GM where lieing lol

Im sure that's with the 6.2 and sm246 or 700r4

hicktownhotrodder · 05-10-2009, 06:54 PM

12 mpg? hell, i only get 9 with my stock 350 and 4.56 rear end

OrangeAnimal · 05-10-2009, 07:14 PM

Yeah 4.56 haha I am surprised you get that much.

My 425 HP Mustang that ran 12's on street tires got better mileage than the truck and that was with 4.10's and 5 speed. So I looked up on fuel economy.gov and found that 12-15 is what You should expect with these trucks. So I guess I am only slightly behind on those numbers.

3r!c84 · 05-10-2009, 08:23 PM

i think its gas motor ?
look this is with the diesel

http://www.73-87.com/7387info/ads_GM...r_on_earth.jpg

grinch4om · 05-10-2009, 08:24 PM

mine was a stock 305, 7oor4 and got 13.5, put a 454,700r4, headers,3"exhaust, weiand,holley, yadda yadda and guess what? 12 3.42:1 gear

Doug's68SS · 05-10-2009, 08:34 PM

Beleave it or not back in the mid 80's my 68 LWB with a 396 and 3.73 gears got 17 mpg when I put a brand new Holley Economaster for a BBC on it. I still have the motor and Carb setting in the Corner. I might should think hard about putting it back in when I finish my truck.

gchemist · 05-10-2009, 08:56 PM

Mine just averaged near 19 MPG doing 70!! Ya need some work on the carb. You should bring it to Austin! Oh, the cruise speed at 70 is 1950 RPMs. Yea OD makes a difference.

Manbearpig · 05-10-2009, 09:19 PM

Quote:

Originally Posted by 3r!c84

i think its gas motor ?
look this is with the diesel

http://www.73-87.com/7387info/ads_GM...r_on_earth.jpg

A square body suburban with a 6.2 and a 5 speed getting 20mpg city would be awesome!

OrangeAnimal · 05-10-2009, 10:03 PM

Hum I wonder if anyone has some suggestions on the jetting for the Edelbrock carb. I could go with fuel injection but what a pain and who makes a good kit? I looked at Holley Pro Jection but I don't really see it being right for what I am going for.

I also have been thinking about going to a 200R4 that is what I did with my El Camino but it was a pain in the ass. I like the OD from GearVendors but boy it's pricey. And you have to shorten the drive shaft. The 200R4 goes in without shortening the drive shaft. Anyway that is all together another topic.

*78 Chevyrado* · 05-10-2009, 10:07 PM

A lot of it is the crappy fuel. I used to get 16-17mpg out of my 3/4 ton with a 350 and now I usually get 13mpg or so unless i get a good tank of gas.
On my stock 350 with a 1406 carb I changed my primary jets/ rods to go one step leaner in the instruction manual.

If you don't have OD running 70-75 mph will get worse mileage than on the back roads. I get better mileage around 55-60mph. Anything over that with no OD and my mileage drops to 8-9mpg.

88 Dippy · 05-10-2009, 10:08 PM

with the 700R4 i get 17mpg average with a 70/40 mix of highway/ city driving

this is with 4.10:1 rear

pig rig · 05-10-2009, 11:17 PM

my crew cab with the big block gets 14 towing, empty, 75mph its all the same no matter how I'm driving it. I'D look into dialing in your carb a little along with a econemy type tune if your after gas milage

I hear people say "I just bought this 1ton dually and it only gets 10mpg I don't think I can aford to drive it" and the only thought that come's to my mind is what'd you think your buying? a smartcar!

77shortybawx · 05-10-2009, 11:28 PM

is it possible that the gas was better quality back then?

pig rig · 05-10-2009, 11:59 PM

yea the quality of gas has dropped off a lot in the last 5 years with all the clean air acts that the oil refinerys have had to meet in the last 3 years and I think they have another emission standerd to meet in 2012

88 Dippy · 05-11-2009, 12:05 AM

back then there was no ethanol in gas. now there is a minimum of 10% unless it says other wise on the pump. i can always see a rais in MPG when i use ethanol free gas (abought 2-3 MPG)

also i wa expecting my tuck to get 8mpg with the 4.10 gears the 17 was a pleasant surprise

MylilBowTie · 05-11-2009, 01:48 AM

What size tires with those 4.10 gears?

88 Dippy · 05-11-2009, 02:28 AM

Quote:

Originally Posted by MylilBowTie

What size tires with those 4.10 gears?

they say 30" on them but when i messured them they came to 30.5"

**78 Big10 454** · 05-11-2009, 03:18 AM

I get 12 mpg in my dreams.....(sigh).

68GMC454 · 05-11-2009, 05:13 AM

i was happy to get 6 to 8 on a good day with my ol 84, loaded or empty, but best truck i ever owned..

OrangeAnimal · 05-11-2009, 07:56 AM

I didn't buy it to get gas mileage but I just figured it should get better than it does. From what I am reading I am getting about average compared to others except for some folks getting 17 mpg or so. I think I should be able to squeeze 15mpg out of it. The other thing that might make it better is putting more miles on the engine. It currently only has about 600 miles on it so there is a possibility that it will loosen up.

05-10-2009, 05:52 PM	#1
OrangeAnimal Registered User Join Date: Jan 2009 Location: New Orleans, LA Posts: 702	12 mpg Help!! I drove my truck this weekend to houston and back. About 220 miles round trip. Burned almost 2 tanks of gas. 16 gallon tank. The engine is pretty much stock. 350 4 bolt main, RV cam (wish I had specs) Flat top pistons, 1.94/1.50 valves stock heads. Edelbrock Performer EPS intake, Edlebrock Performer Carb. Timing is set base 8, Vacuum Advance hooked to full vacuum limited to 14 at idle, My full mechanical timing is 32* My full vacuum timing no load is 42* degrees. I spent alot of time working on it and have not gotten the mileage any better. My rear end is a 3.07 open diff. I am lowered 5/7 running 20's with a 28 inch total tire diameter. At 65 mph I am running 2300 rpm could this be the culprit? I didn't think is was too high rpm. I Figured this thing would get better mileage than this. I could be wrong though. I guess it could be a jetting issue as well. It's a 1406 carb. Anyone have a good starting point for the jetting or should I ditch this for the Fuel injection if I am looking for mileage? I also noticed one other issue. It is too rich once it's warmed up good floods easy when try to start it. I hadn't ever had this problem b4 the trip to Houston. Any thoughts or ideas would be great. __________________ 82 Chevy SWB "OrangeAnimal" Lot of Goodies! Sold 93 GMC 1500 "Angry Red" 383 TBI Powered Fun! 300hp/410ft.lbs. 09 Yaris wife's daily.

05-10-2009, 05:59 PM	#2
3r!c84 Badass Join Date: Jan 2009 Location: lox. fl Posts: 4,586	Re: 12 mpg Help!! i have the same thing on my truck and its all stock,with the 305 and th350 and im runing the stock tire size,stock gearing. when i went to daytona i got 12.7 -13 mpg? and i was only going 60-65mph __________________ Think outside the box? -84c10 (1stcar)→My Build← -00 Saturn 5spd drop a gear and disappear! 1/4:13:90

05-10-2009, 06:11 PM	#3
OrangeAnimal Registered User Join Date: Jan 2009 Location: New Orleans, LA Posts: 702	Re: 12 mpg Help!! Well crap thats no good. I am sure that these trucks got better highway mpg than that. __________________ 82 Chevy SWB "OrangeAnimal" Lot of Goodies! Sold 93 GMC 1500 "Angry Red" 383 TBI Powered Fun! 300hp/410ft.lbs. 09 Yaris wife's daily.

05-10-2009, 06:16 PM	#4
3r!c84 Badass Join Date: Jan 2009 Location: lox. fl Posts: 4,586	Re: 12 mpg Help!! yea but with no O/D they rev high going down the highway idk about the trucks with the 700r4's look at this http://www.73-87.com/7387info/ads_GM/82_20mpg.jpg you know the guys at GM where lieing lol __________________ Think outside the box? -84c10 (1stcar)→My Build← -00 Saturn 5spd drop a gear and disappear! 1/4:13:90

05-10-2009, 06:17 PM	#5
pokethesmot profeshinaly unimployed Join Date: Dec 2008 Location: hazlehurst, GA Posts: 1,232	Re: 12 mpg Help!! i have a sbc 400 and thats about what i get __________________ my ride click here my myspace "having mud flaps is like asking for a smaller trophy"

05-10-2009, 06:54 PM	#7
hicktownhotrodder Rollin Coal Join Date: May 2009 Location: Winnebago Illinios Posts: 131	Re: 12 mpg Help!! 12 mpg? hell, i only get 9 with my stock 350 and 4.56 rear end

05-10-2009, 07:14 PM	#8
OrangeAnimal Registered User Join Date: Jan 2009 Location: New Orleans, LA Posts: 702	Re: 12 mpg Help!! Yeah 4.56 haha I am surprised you get that much. My 425 HP Mustang that ran 12's on street tires got better mileage than the truck and that was with 4.10's and 5 speed. So I looked up on fuel economy.gov and found that 12-15 is what You should expect with these trucks. So I guess I am only slightly behind on those numbers. __________________ 82 Chevy SWB "OrangeAnimal" Lot of Goodies! Sold 93 GMC 1500 "Angry Red" 383 TBI Powered Fun! 300hp/410ft.lbs. 09 Yaris wife's daily.

05-10-2009, 08:23 PM	#9
3r!c84 Badass Join Date: Jan 2009 Location: lox. fl Posts: 4,586	Re: 12 mpg Help!! i think its gas motor ? look this is with the diesel http://www.73-87.com/7387info/ads_GM...r_on_earth.jpg __________________ Think outside the box? -84c10 (1stcar)→My Build← -00 Saturn 5spd drop a gear and disappear! 1/4:13:90

05-10-2009, 08:24 PM	#10
grinch4om dang its hot Join Date: Nov 2006 Location: frankfort kentucky Posts: 1,349	Re: 12 mpg Help!! mine was a stock 305, 7oor4 and got 13.5, put a 454,700r4, headers,3"exhaust, weiand,holley, yadda yadda and guess what? 12 3.42:1 gear

05-10-2009, 08:34 PM	#11
Doug's68SS Registered User Join Date: May 2009 Location: Canton, Tx Posts: 175	Re: 12 mpg Help!! Beleave it or not back in the mid 80's my 68 LWB with a 396 and 3.73 gears got 17 mpg when I put a brand new Holley Economaster for a BBC on it. I still have the motor and Carb setting in the Corner. I might should think hard about putting it back in when I finish my truck.

05-10-2009, 08:56 PM	#12
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	Re: 12 mpg Help!! Mine just averaged near 19 MPG doing 70!! Ya need some work on the carb. You should bring it to Austin! Oh, the cruise speed at 70 is 1950 RPMs. Yea OD makes a difference. __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

05-10-2009, 10:03 PM	#14
OrangeAnimal Registered User Join Date: Jan 2009 Location: New Orleans, LA Posts: 702	Re: 12 mpg Help!! Hum I wonder if anyone has some suggestions on the jetting for the Edelbrock carb. I could go with fuel injection but what a pain and who makes a good kit? I looked at Holley Pro Jection but I don't really see it being right for what I am going for. I also have been thinking about going to a 200R4 that is what I did with my El Camino but it was a pain in the ass. I like the OD from GearVendors but boy it's pricey. And you have to shorten the drive shaft. The 200R4 goes in without shortening the drive shaft. Anyway that is all together another topic. __________________ 82 Chevy SWB "OrangeAnimal" Lot of Goodies! Sold 93 GMC 1500 "Angry Red" 383 TBI Powered Fun! 300hp/410ft.lbs. 09 Yaris wife's daily.

05-10-2009, 10:07 PM	#15
78 Chevyrado Account Suspended Join Date: Dec 2007 Location: Unnapreciative, Trollville Posts: 2,079	Re: 12 mpg Help!! A lot of it is the crappy fuel. I used to get 16-17mpg out of my 3/4 ton with a 350 and now I usually get 13mpg or so unless i get a good tank of gas. On my stock 350 with a 1406 carb I changed my primary jets/ rods to go one step leaner in the instruction manual. If you don't have OD running 70-75 mph will get worse mileage than on the back roads. I get better mileage around 55-60mph. Anything over that with no OD and my mileage drops to 8-9mpg.

05-10-2009, 10:08 PM	#16
88 Dippy Registered User Join Date: Feb 2009 Location: mt. Pleasant, MI Posts: 246	Re: 12 mpg Help!! with the 700R4 i get 17mpg average with a 70/40 mix of highway/ city driving this is with 4.10:1 rear __________________ 1974 chevy Cheyenne C10 "The Mutt":4x4 convertion, NP208, 700-R4, stock 350, edelbrock Torker intake, edelbrock 600 CFM carb, duels 2001 Pontiac Grand Prix GT: 3.8L supercharged, 9.2:1 comprestion, ZZP XP cam, home made intake, 2 1/2" exhuast, 10psi of boost

05-10-2009, 11:17 PM	#17
pig rig Registered User Join Date: Feb 2009 Location: washington the state Posts: 730	Re: 12 mpg Help!! my crew cab with the big block gets 14 towing, empty, 75mph its all the same no matter how I'm driving it. I'D look into dialing in your carb a little along with a econemy type tune if your after gas milage I hear people say "I just bought this 1ton dually and it only gets 10mpg I don't think I can aford to drive it" and the only thought that come's to my mind is what'd you think your buying? a smartcar! __________________ my sports car rolls on six wheels only because I'm to fat to get in and out of new corvette http://hubgarage.s3.amazonaws.com/ph...ped_detail.JPG



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05-10-2009, 11:28 PM	#18
77shortybawx Registered User Join Date: Jan 2009 Location: belmond Posts: 22	Re: 12 mpg Help!! is it possible that the gas was better quality back then?

05-10-2009, 11:59 PM	#19
pig rig Registered User Join Date: Feb 2009 Location: washington the state Posts: 730	Re: 12 mpg Help!! yea the quality of gas has dropped off a lot in the last 5 years with all the clean air acts that the oil refinerys have had to meet in the last 3 years and I think they have another emission standerd to meet in 2012 __________________ my sports car rolls on six wheels only because I'm to fat to get in and out of new corvette http://hubgarage.s3.amazonaws.com/ph...ped_detail.JPG

05-11-2009, 12:05 AM	#20
88 Dippy Registered User Join Date: Feb 2009 Location: mt. Pleasant, MI Posts: 246	Re: 12 mpg Help!! back then there was no ethanol in gas. now there is a minimum of 10% unless it says other wise on the pump. i can always see a rais in MPG when i use ethanol free gas (abought 2-3 MPG) also i wa expecting my tuck to get 8mpg with the 4.10 gears the 17 was a pleasant surprise __________________ 1974 chevy Cheyenne C10 "The Mutt":4x4 convertion, NP208, 700-R4, stock 350, edelbrock Torker intake, edelbrock 600 CFM carb, duels 2001 Pontiac Grand Prix GT: 3.8L supercharged, 9.2:1 comprestion, ZZP XP cam, home made intake, 2 1/2" exhuast, 10psi of boost

05-11-2009, 01:48 AM	#21
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	Re: 12 mpg Help!! What size tires with those 4.10 gears? __________________ 1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI

05-11-2009, 03:18 AM	#23
78 Big10 454 78 Big10 454 Join Date: Jul 2008 Location: Pismo Beach, CA Posts: 839	Re: 12 mpg Help!! I get 12 mpg in my dreams.....(sigh).

05-11-2009, 05:13 AM	#24
68GMC454 THE VILLIAGE IDIOT Join Date: Nov 2006 Location: Tooele, Utah Posts: 1,405	Re: 12 mpg Help!! i was happy to get 6 to 8 on a good day with my ol 84, loaded or empty, but best truck i ever owned.. __________________ honestly honey,,i have no idea how that truck got here. Last edited by 68GMC454; 05-11-2009 at 05:13 AM.

05-11-2009, 07:56 AM	#25
OrangeAnimal Registered User Join Date: Jan 2009 Location: New Orleans, LA Posts: 702	Re: 12 mpg Help!! I didn't buy it to get gas mileage but I just figured it should get better than it does. From what I am reading I am getting about average compared to others except for some folks getting 17 mpg or so. I think I should be able to squeeze 15mpg out of it. The other thing that might make it better is putting more miles on the engine. It currently only has about 600 miles on it so there is a possibility that it will loosen up. __________________ 82 Chevy SWB "OrangeAnimal" Lot of Goodies! Sold 93 GMC 1500 "Angry Red" 383 TBI Powered Fun! 300hp/410ft.lbs. 09 Yaris wife's daily.

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