is 10 mpg normal? - Page 3 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tekno62 · 03-22-2009, 09:08 PM

Need some help- Im confused. I just jacked up the truck - I kept one tire from not moving I get 1 and 1/3 tire spin to one drive line spin. the truck is to have posi from what the spid shows but when I turned the tire the other side would spin in the other direction.

Quote:

Originally Posted by Woody

The quickest way to check your gear ratio is to jack up both rear tires, then turn the drive shaft and count the turns it takes to rotate the tires one full turn. make sure both tires are turning. So then 3 - 3/4 turns of hte drive shaft for 1 rotations of the the tires is a 3.73 gear. a little over 4 is probably a 4.11, a little over 3 is probably 3.08.

You also can look at the glove box sticker, it may have it listed if it is still there and the rearend hasn't been swapped out.

Oh! I have a 350 / 400t w/ 3.73 gear and it only got 12mpg. I installed a 305 (from a 86 chevy) with HEI and the best I could ever get was 13-13.5 on the highway running 65-70. Like everyone else it really does not matter if it was loaded or not....

72chevyk10 · 03-22-2009, 11:41 PM

Quote:

Originally Posted by tekno62

Need some help- Im confused. I just jacked up the truck - I kept one tire from not moving I get 1 and 1/3 tire spin to one drive line spin. the truck is to have posi from what the spid shows but when I turned the tire the other side would spin in the other direction.

were you spining the driveline or the tires?

nrb's70gmc · 03-22-2009, 11:54 PM

my 3/4 ton 2wd gets 8.5 mpg im not sure of the gear ratio but the this truck is a gas pig it has a crate 350,turbo 350---it might have 4 10s because it can beat a corvette of the line lol

Longhorn Man · 03-23-2009, 12:01 AM

if your C/20 was originally built with the 350/350, then it should have 4.10's out back.
Exactly what year vette is it beating off the line?

nrb's70gmc · 03-23-2009, 03:31 PM

wow thanks for the info now im sure before i never knew (well i dont think it could beat a corvette but with the parts i have on the engine it sure is quick off the line) when its not raining

tekno62 · 03-23-2009, 07:38 PM

I spun the tire and watched the drive line. only had one tire spinning.

Quote:

Originally Posted by 72chevyk10

were you spining the driveline or the tires?

boundstaffpress · 03-23-2009, 09:33 PM

My 283 gets 12mpg in town with 3.73 posi 4x4. On my last road trip, I averaged 15.5 mpg.

**68350** · 03-23-2009, 09:45 PM

I believe you have to spin the driveshaft for this to work out right. Make sure you clearly mark the tire to get a good guess. I have gotten anywhere from 8-16 mpg with trucks we've owned. Suprisingly, a 72 sb with 402/th400/3.08 was gettin 15! On average, I would say 12-13 for a stocker tuned well.

Gray Ghost · 03-23-2009, 10:40 PM

I used to really hate reading these threads...all the claims of big mileage in flying boxes with BB's and high numerical rear axles....now I just chuckle. Must be that new math.

tekno62 · 03-23-2009, 11:48 PM

Quote:

Originally Posted by Gray Ghost

I used to really hate reading these threads...all the claims of big mileage in flying boxes with BB's and high numerical rear axles....now I just chuckle. Must be that new math.

new math is how the government keeps running

tranz am · 03-24-2009, 12:03 AM

Im getting about 16 - 17mpg on the highway with a 350,T5 trans and 3:90's out back.

Gray Ghost · 03-24-2009, 07:03 PM

I hear ya...especially this one!

piecesparts · 03-24-2009, 08:17 PM

Honest, I put $2.00 in last week, but there is still half a tank.

03-22-2009, 11:54 PM	#53
nrb's70gmc Registered User Join Date: Sep 2008 Location: magalia,ca Posts: 366	Re: is 10 mpg normal? my 3/4 ton 2wd gets 8.5 mpg im not sure of the gear ratio but the this truck is a gas pig it has a crate 350,turbo 350---it might have 4 10s because it can beat a corvette of the line lol __________________ 1970 2wd 3/4 ton- 2004 crate 350 thorley tri-y headers-edelbrock performer eps manifold 600cfm performer carb, crane cams energizer cam,lifters, dual 2.5 magnaflows, mallory HEI, powermaster 140 amp altenator, griffen aluminum radiator.(8 MPG)

03-23-2009, 12:01 AM	#54
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: is 10 mpg normal? if your C/20 was originally built with the 350/350, then it should have 4.10's out back. Exactly what year vette is it beating off the line?

03-23-2009, 03:31 PM	#55
nrb's70gmc Registered User Join Date: Sep 2008 Location: magalia,ca Posts: 366	Re: is 10 mpg normal? wow thanks for the info now im sure before i never knew (well i dont think it could beat a corvette but with the parts i have on the engine it sure is quick off the line) when its not raining __________________ 1970 2wd 3/4 ton- 2004 crate 350 thorley tri-y headers-edelbrock performer eps manifold 600cfm performer carb, crane cams energizer cam,lifters, dual 2.5 magnaflows, mallory HEI, powermaster 140 amp altenator, griffen aluminum radiator.(8 MPG)

03-23-2009, 09:33 PM	#57
boundstaffpress Jamie Hyneman is my twin Join Date: Nov 2005 Location: La Junta, Colorado Posts: 705	Re: is 10 mpg normal? My 283 gets 12mpg in town with 3.73 posi 4x4. On my last road trip, I averaged 15.5 mpg. __________________ Justin SOLD 1967 K10 Fleetside, 283, Front and Rear Posi SOLD Color Wiring Diagrams Now in High Resolution V8 and Cab and Cab and Chassis

03-23-2009, 09:45 PM	#58
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: is 10 mpg normal? I believe you have to spin the driveshaft for this to work out right. Make sure you clearly mark the tire to get a good guess. I have gotten anywhere from 8-16 mpg with trucks we've owned. Suprisingly, a 72 sb with 402/th400/3.08 was gettin 15! On average, I would say 12-13 for a stocker tuned well. __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

03-23-2009, 10:40 PM	#59
Gray Ghost Senior Member Join Date: Sep 2004 Location: Terrell, TX Posts: 1,967	Re: is 10 mpg normal? I used to really hate reading these threads...all the claims of big mileage in flying boxes with BB's and high numerical rear axles....now I just chuckle. Must be that new math. __________________ Kelly '05 GMC Sierra SLE Z71 Bone stock except for new bed rail caps.

03-24-2009, 12:03 AM	#61
tranz am Registered User Join Date: Apr 2007 Location: Santa Rosa, Ca Posts: 586	Re: is 10 mpg normal? Im getting about 16 - 17mpg on the highway with a 350,T5 trans and 3:90's out back. __________________ My build thread http://67-72chevytrucks.com/vboard/s...d.php?t=456220 Best 1/4 mile time 12.1 @ 111 w/traction issues 1969 GMC SWB 1964 chevy II Nova ht Last edited by tranz am; 03-24-2009 at 12:03 AM.

03-24-2009, 07:03 PM	#62
Gray Ghost Senior Member Join Date: Sep 2004 Location: Terrell, TX Posts: 1,967	Re: is 10 mpg normal? I hear ya...especially this one! __________________ Kelly '05 GMC Sierra SLE Z71 Bone stock except for new bed rail caps.

03-24-2009, 08:17 PM	#63
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: is 10 mpg normal? Honest, I put $2.00 in last week, but there is still half a tank.



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