Honest answers for your Longbed 350 Mileage?

[2bits]

OK I say "honest" because I know people like to brag at how great or at the same time complain about how terrible their mileage is. I am just lookin for honest answers for what you feel like you are getting.

Here's the criteria, it is pretty middle of the road so there should be plenty, but if you don't fit in the catagory, feel free to post just note differences (like if you dropped in a 4 speed .

•350 engine
•350 Tranny
•Note 2bbl or 4bbl, and axle ratio if known
•Note other differences


That's It!
Thanks for your help! (I am looking to pick up a longbed vs a shortbed)

[TwoFiftyShifter]

1987 K20.
350 TBI, 4-speed SM465, 3.73 axle ratio, 245-75R16 tires.

In town. I've had 10mpg with a lot of stop lights or a heavy foot. With minimal stop lights, 13mpg is acheiveable in town.

Highway. Lots of hills on the highways here, a steady 15mpg at 60mph. By 70mph, your at 13ish mpg.

[Justins76]

350 4bbl, th350, 29" tires, 3.42 gears about 8-10mpg

[BIG10]

I don't quite fit and this probably won't help you, but here it is anyway.

1978 BIG10 longbed
355, GMPP intake, Edelbrock 600
700R4 (makes all the difference)
3.42 axle (originally 3.73)
235/75/15 tires

The only time I recorded the mileage was the trip home after I bought it. I filled up both tanks and drove 700 miles without stopping for gas. Stopped for food, but not for gas. Had the cruise set most of the way at 65-70. I used right at 40 gallons which calculates to 17.5 mpg. I was thrilled since my wife's six-cylinder Trailblazer struggles to average 15-16.

My normal in-town driving would probably produce 10-12 mpg.

[TexasJeff]

1980 GMC 3/4 ton Sierra Grande
350cid rebuilt stock about 40,000 miles since rebuild
turbo 350 non electronic over drive (came from factory with electronic over drive)
rear end gear 3.73
Tires LT-285-75R16 50 pounds of pressure

I get 10-12mpg all the time, I pull a small pop-up camper on the highway most of the time and driving around town, but the mileage stays at those numbers no matter what.

[68 TT]

78 K20
350 with mild cam (280 degrees .480" lift), RPM intake
750 vac sec Demon carb with 14x4 K&N filter
SM-465 4-speed
NP205 transfer case
14-bolt and Dana 44 with 5.13 gears
32" tires on 16" aluminum rims
headers & 2-1/2" dual exhaust
7-blade clutch fan

10 mpg in town no matter how much weight is in it
13 mpg at 60 mph
12 mpg at 70 mph

The gearing really kills highway mileage. A similar built 81 I had got 15 on the freeway at 70 mph with 4.10 gears but got the same 10 mpg in the city.

[old Rusty C10]

1982 C 10 2wd
305 motor ( basically same as a 350)
th 350 trans
unknown rear gears, but its a heavy half
aftermarket carb and manifold by edelbrock
Im lucky to get 8 mph in city and 15 highway.. cost me $50 to go between NYC and Binghamton

[C-10 simplex]

Please read this thread thoroughly:

This is a very scientific, thorough, anal, study i made last year and it's still in progress. i bought the digital speedo specifically to measure mpg because of it's acuracy.

http://forum.73-87chevytrucks.com/sm...p?topic=8474.0


In a nutshell:
Completely stock 350 crate engine with stock quadrajet, no computers whatsoever
TH-350C (with lockup converter)
2.56 rear gear
longbed

Roughly 16 mpg average.





2) i don't think shortbed vs. longbed is going to make much of a difference in MPG; Sure the shorty is a little lighter, but i don't feel this is going to make a significant difference.

3) i think tires can and will make all the difference in the world; i'm thinking of stopping by the dealer and seeing what kind of tire these new silverado XFE's are using.
i will probably have to go while it's dark though because everytime i go to the dealer just to look at something all the sales people swarm around me like sharks. It's unerving.
a) i also feel that running the smallest tire possible, without affecting the gear ratio too much, will also help significantly.

[Shon]

1971 C10 LWB 350 w/ Q-jet/TH350 3.09 gear

I got 13MPGs around town to/from work. I did do an extreme test and cut it off at lights and put it in N down hills and got it to 15MPGs.

[68 TT]

Originally Posted by C-10 simplex

Please read this thread thoroughly:

This is a very scientific, thorough, anal, study i made last year and it's still in progress. i bought the digital speedo specifically to measure mpg because of it's acuracy.

http://forum.73-87chevytrucks.com/sm...p?topic=8474.0


In a nutshell:
Completely stock 350 crate engine with stock quadrajet, no computers whatsoever
TH-350C (with lockup converter)
2.56 rear gear
longbed

Roughly 16 mpg average.





2) i don't think shortbed vs. longbed is going to make much of a difference in MPG; Sure the shorty is a little lighter, but i don't feel this is going to make a significant difference.

3) i think tires can and will make all the difference in the world; i'm thinking of stopping by the dealer and seeing what kind of tire these new silverado XFE's are using.
i will probably have to go while it's dark though because everytime i go to the dealer just to look at something all the sales people swarm around me like sharks. It's unerving.
a) i also feel that running the smallest tire possible, without affecting the gear ratio too much, will also help significantly.

Tires definitely have a big effect on MPG. On my 90 Z71 it dropped 1 to 2 mpg with each increase in tire size. With 31x10.50's it got close to 14 in the city, with 32x11.50's it went down to 12 and with 33x12.50's it went down to about 10.5 in the city. I recalibrated the speedo every time so it was not just speedo error. I'm sure a gear change would have helped that out a little.

[cableguy0]

84 gmc 1/2 ton was a diesel.
now 355 10-1 compression
200cc aluminum heads
large hydraulic roller cam 238/246@.050 .548 lift
victor jr intake
proform 750 vac secondaries carb
3.42 gear th350 w/ 2500 stall converter.
235/75/15 tires
11mpg mixed driving mostly highway.

[chicklin]

1986 K10 Suburban
Stock 350ci
700r4
3.42 gears
31" tires
about 70% interstate, 30% street

......8mpg

Yes, something is wrong. If anybody can tell me how to lean out a Quadrajet, I'd love to hear. No, it's not the idle mixture screws and the choke is fully open when warm.

[68 TT]

Originally Posted by chicklin

1986 K10 Suburban
Stock 350ci
700r4
3.42 gears
31" tires
about 70% interstate, 30% street

......8mpg

Yes, something is wrong. If anybody can tell me how to lean out a Quadrajet, I'd love to hear. No, it's not the idle mixture screws and the choke is fully open when warm.

You could have a dragging emergency brake. I had that happen once. The pedal was released but the cable had corroded some and did not release the brake all the way. It just felt a little sluggish so I started checking things out and found it. Pull your wheels and see how easy your drums spin with it in neutral.

Check your front wheels too while you are at it. I have seen a few different things go wrong up front and cause the wheels to not spin freely like they should.

[swb85]

1985 silverado short bed 2wd
-383ci, 10.4:1, vortec heads, 232/238 .544"/.555" hyd roller, rpm air gap, 750cfm edel carb
-m21 muncie 4 speed
-10 bolt w/3.42 gears, 28" tall tires

Usually average around 14-15mpg with roughly equal city/highway miles. Pure highway 70mph trips nets around 17mpg. If I grandpa drive in the slow lane (55-60mph) I can get 18-19mpg, but that's boring.

[dga93]

78 C10 350/350/Qjet
all original.
wheels 275/60/17

8-10mpg

[donut]

'73 K-20
350- Vortec heads, Summit 1103 cam, E-bay dual plane intake, Q-jet, HEI, headers, dual exhaust w/crossover.

Turbo 350 (shift kit)
NP205 transfer case
4.10 gears, 30" tall tires (245/75-16)
No-dump, dump bed instead of pickup bed.

10-12 mpg.

[cableguy0]

After seeing all these stock trucks getting less mpg than me i dont feel so bad.

[78-5.3]

i cant wait to take my 5.3 out on the road im expecting 18-21 mpg

[vtwinsport]

76 350 stock block & heads (for now), edelbrock intake and carb, hedman headers, 350 with stock converter (never been checked for proper operation), sloppy 3.08 rear, 27 inch tires; 6-8mpg.

[409sbc pwr]

84 swb 4x4, 35x13.50s, 6inch lift, 409sbc 2.02 heads, flat top pistons, .480 lift cam with 108 lsa, street avenger holley and i think they r 3.08 gears

6 MILES PER GALLON WITH 92 OCTANE!!!!! you gotta pay to play

[nekkidhillbilly]

od is the key

[87Square10]

I put in a built 355 runing about 10:1 compression and an edlebrock 650 carb wiend intake long tube headers and running a 3 speed. i get about 7-8 mpg highway running at 70 im pushing about 35-3600 rpm

[BIG10]

Originally Posted by nekkidhillbilly

od is the key

Yesiree.

[Benelli]

I don't get it....

350 with .06 bore, Weinald Alum Dual plane intake, 650 Holley truck avenger carb, a very, very mild cam, TH350 w/shift kit NP203 T-case with Part time and Hubs, 3.40 gear ratio according to glove box, 31x10.5R15 tires. This is all on a 1979 K10 Longbox.

If I drive like I'm in a damn Buick I get 7 MPG. How in God's name are you guys getting in the double digits? Hell some of you guys get 10+ with a damn 3 speed. I'm jealous. What can I do?

What's wrong? This is mostly 50-55mph 10 miles to town, then 2 miles going 30 and a stoplight here and there, then 1 mile going 30 with slowing down to turn into the school parking lot. I don't romp on it, I usually let it hit 2000 rpms before it changes gears. It's pretty flat out here, I hardly have to "get on it" to get up to speed. It runs like a beast. How much will running rich have on gas mileage? It'll shoot black-fog during cold morning. You can see a spray of black spots in the snow.

HELP PLEASE. I hope I'm not "thread-jacking"

[IMG][/IMG]

HELP.

[78 Chevyrado]

on my 78 c20 when it had the 5.5 inch wide skinny tires and before they watered down the gas I got around 15-16MPG regularly. Nowadays with the wider tires and the sometimes here and there watered down gas, I get from 8MPG-13MPG depending on where I fill up.

Oh and the truck has a TH400 and 3.73 rear end

My dad told me once, you wanna save gas drive like there's an egg under your foot and you don't wanna break it.

I also made the experiment of driving with the vaccum gauge hooked up. The game goes like this; try to take off from a stop while making that vaccum gauge move as little as possible. it can't be done without moving it so you just try to move it as little as possible. and the gauge moves relative to how much you press the pedal down.