str8 6 help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

lil blue · 02-15-2010, 10:18 PM

does anybody know how to get good gas mileage from this motor cause i dont even think im getting 10 in the city
any kind of help would help

tecky11 · 02-15-2010, 11:08 PM

250 or 296 st8 6 auto or manual, what is your reaer end ratio, 1bbl or 2bbl carb

lil blue · 02-15-2010, 11:14 PM

Quote:

Originally Posted by tecky11

250 or 296 st8 6 auto or manual, what is your reaer end ratio, 1bbl or 2bbl carb

its a 250 1bbl auto and i dont know my rear end ratio but it was getting around 10 mpgs now i dont even want to know

tecky11 · 02-15-2010, 11:22 PM

I THINK that you have a 3.08 rear, and should be geting better that 10, i get 10MPG with my 351 CI V8 in my full size f$rd!!!!!

68GMCCustom · 02-15-2010, 11:47 PM

keep it tuned up and your tires properly inflated.

lil blue · 02-16-2010, 07:27 AM

i always keep the tires full i should get a 350 get the same mpg but more power

bigblockorange · 02-16-2010, 07:35 AM

I installed a HEI and went with a larger air cleaner. I also put a higher geared rear in it. My buddy had a 4 on the tree and was able to go with a higher gear ratio and also ran taller tires.

69GMCLonghorn · 02-16-2010, 02:56 PM

What a lot of people forget to verify is that their speedo is reading correctly. Maybe you are only getting 10 MPG, but with the number of screwed up speedo's I've seen, get it calibrated, then figure out what you have. I was off by 30% in mine!!!

If it is accurate and you're still barely getting 10 MPG, start troubleshooting, tuning up and doing all the little crap that most people will suggest... Here are some questions to answer for yourself.

Are the float(s) leaking in the carb causing it to run fat? Or some other carb issue?
Has the mileage changed recently or has it always sucked?
Do your driving habits cause the mileage to change very much?

lil blue · 02-16-2010, 10:49 PM

no i just checked it like 10 mins ago its right and i drive it so slow people fly past me leaving the red lights i know its not the way i drive

lil blue · 02-16-2010, 10:53 PM

i had the motor tuned one time and i did really good for about 2 weeks then it went to crap and i didnt touch anything

jsmithbm · 02-17-2010, 12:42 AM

is there smoke coming out the tailpipe if so what color? Is there a fuel leak? Check the gap on your sprak plugs. There are a lot of little things you can do. i know a rebuild kit for the carb is less than 20 bucks.
I was getting about 16 mpg in my 6-er. Then the carb went south on me.

Shaky · 02-17-2010, 06:08 AM

The Rochester Carburetors book has a small section on Monojet Economy Modifications. It says to increase the main jet size one or two sizes, plug the APT, and cut not more than two full coils from the power spring.

That said, you should be getting better mileage already without these mods.

An HEI helps a little too.

02-15-2010, 10:18 PM	#1
lil blue Registered User Join Date: Dec 2008 Location: orlando fl Posts: 203	str8 6 help does anybody know how to get good gas mileage from this motor cause i dont even think im getting 10 in the city any kind of help would help __________________ 1978 c10 stepside Last edited by lil blue; 02-15-2010 at 10:18 PM.

02-15-2010, 11:08 PM	#2
tecky11 Registered User Join Date: Jan 2009 Location: phoenix,AZ Posts: 451	Re: str8 6 help 250 or 296 st8 6 auto or manual, what is your reaer end ratio, 1bbl or 2bbl carb

02-15-2010, 11:22 PM	#4
tecky11 Registered User Join Date: Jan 2009 Location: phoenix,AZ Posts: 451	Re: str8 6 help I THINK that you have a 3.08 rear, and should be geting better that 10, i get 10MPG with my 351 CI V8 in my full size f$rd!!!!! Last edited by tecky11; 02-15-2010 at 11:51 PM. Reason: wrong engine size

02-15-2010, 11:47 PM	#5
68GMCCustom Truck and auto performance nut Join Date: Feb 2007 Location: McKinney,Texas Posts: 3,848	Re: str8 6 help keep it tuned up and your tires properly inflated. __________________ Kurt - '68 GMC short step - NIB '09 LY6 6.0L crate motor w/mods, NIB '12 crate 4L85e w/billet 3k stall Circle D, 3.73 posi 12 bolt, DynaTech f-swap headers, 3/4 drop, handling mods, etc. - my toy '72 Chevy LWB C-10 Highlander - 350/350 ps/pb/tilt/ac - not original but close '06 Chevy TrailBlazerSS - LS2/4L70e - little black hot rod SUV - my DD '18 Kia Sorento - wife's econo-driver '95 Chevy S10 - reg cab shortbed, LS, 4.3, auto... my '68's powertrain and chassis build -links broken A surprise phase - carb to efi -links broken

02-16-2010, 07:27 AM	#6
lil blue Registered User Join Date: Dec 2008 Location: orlando fl Posts: 203	Re: str8 6 help i always keep the tires full i should get a 350 get the same mpg but more power __________________ 1978 c10 stepside

02-16-2010, 07:35 AM	#7
bigblockorange Senior Member Join Date: Jan 2007 Location: central pa Posts: 428	Re: str8 6 help I installed a HEI and went with a larger air cleaner. I also put a higher geared rear in it. My buddy had a 4 on the tree and was able to go with a higher gear ratio and also ran taller tires. __________________ I guess you could say I’m not really lazy I’m just real good at doing nothing!!!!

02-16-2010, 02:56 PM	#8
69GMCLonghorn Registered User Join Date: Dec 2006 Location: Porter Ranch, CA Posts: 978	Re: str8 6 help What a lot of people forget to verify is that their speedo is reading correctly. Maybe you are only getting 10 MPG, but with the number of screwed up speedo's I've seen, get it calibrated, then figure out what you have. I was off by 30% in mine!!! If it is accurate and you're still barely getting 10 MPG, start troubleshooting, tuning up and doing all the little crap that most people will suggest... Here are some questions to answer for yourself. Are the float(s) leaking in the carb causing it to run fat? Or some other carb issue? Has the mileage changed recently or has it always sucked? Do your driving habits cause the mileage to change very much?

02-16-2010, 10:49 PM	#9
lil blue Registered User Join Date: Dec 2008 Location: orlando fl Posts: 203	Re: str8 6 help no i just checked it like 10 mins ago its right and i drive it so slow people fly past me leaving the red lights i know its not the way i drive __________________ 1978 c10 stepside

02-16-2010, 10:53 PM	#10
lil blue Registered User Join Date: Dec 2008 Location: orlando fl Posts: 203	Re: str8 6 help i had the motor tuned one time and i did really good for about 2 weeks then it went to crap and i didnt touch anything __________________ 1978 c10 stepside

02-17-2010, 12:42 AM	#11
jsmithbm Registered User Join Date: Jun 2009 Location: Newnan, GA Posts: 485	Re: str8 6 help is there smoke coming out the tailpipe if so what color? Is there a fuel leak? Check the gap on your sprak plugs. There are a lot of little things you can do. i know a rebuild kit for the carb is less than 20 bucks. I was getting about 16 mpg in my 6-er. Then the carb went south on me. __________________ Learning as I go! -------------------------------------

02-17-2010, 06:08 AM	#12
Shaky Six in a row makes it go... Join Date: Mar 2009 Location: Vacationland: Maine Posts: 1,346	Re: str8 6 help The Rochester Carburetors book has a small section on Monojet Economy Modifications. It says to increase the main jet size one or two sizes, plug the APT, and cut not more than two full coils from the power spring. That said, you should be getting better mileage already without these mods. An HEI helps a little too. __________________ 67 C20 long step resto: http://67-72chevytrucks.com/vboard/s...d.php?t=342086 66 C10 long step build: http://67-72chevytrucks.com/vboard/s...=1#post3814790 CT to Alaska in a 67 C10: http://67-72chevytrucks.com/vboard/s...d.php?t=399224 “The height of sophistication is simplicity." - Clare Boothe Luce

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