Gas Mileage?

[LSUMurse]

'68 LWB, 307, Powerglide, 3.73's (I think)

I drove it from Austin to New Orleans and got 10 MPG highway once I got out of the foothills around Austin. I have since dropped in a HEI distributor and now get 11.5 MPG on the highway.

[Dean'smeanmachine]

Originally Posted by CC69Rat

Old truck
8 mpg - $400 month gas bill - super cool and makes you happy. No payment. Appreciates monthly, things you add to it make it worth more for the most part. Safe, solid.

New (anything really) 35mpg avg - Gas bill 25% of the truck, BUT ~$500/mo. car payment. + $100 mo. in depreciation, $100 month in intrest. Keep it two years, you're luck to break even. Coolness factor goes way down. You get in any type of accident, you and your family are in more danger of being hurt.


My point being, yes these trucks are gas hogs but apples to apples it doesn't really hurt as bad as it seems. My old GMC gets 22mpg or so. Stock 350, 3OTT. SWB, stock gearing. (feels like 3:55 maybe, non posi. SWB truck, drive like a grandpa and tractor it around a little bit. No high RPM, or twisting it up any at all)

I could buy a new truck and get 22mpg. .. but why? Loose my butt in depreciation ?

My Big Block truck, that will be different absolutely but I don't drive it every day.

I'll keep my wife in the new model car, leather, air conditioning, etc. I'm good with my trucks and put $500 mo into them instead of the payment. Just my .02.

that was the best comment ive ever read. you ROCK

[67ChevyRedneck]

Expect 10-12, consider anything above that a happy bonus

Have a fun and safe trip and take pics for us!!!!

[JasonLS1]

71' nothing special BBC, HEI, TH400, average around 8-10 in town, dont do much highway anyway. Like others have said, id rather pay a high gas bill than a huge monthly payment and full insurance.


jason

[Budda-Boom]

Assuming everything is in good working order, maybe 11-13 city and possibly 14-16 highway.

I owned a '70 C-10 2WD 8' Fleetside with 350 4-bbl/3-speed stick back in the early 70's. I remember getting 15-16 MPG. It didn't seem to matter how it was driven as I recall.

Automatic transmissions used a lot more gasoline back before the days of overdrive and locking torque converters. TH400 equipped vehicles used more gas than ones with a TH350.

[71K20chevy]

My 71 K20 with 4" of lift, 33" tires, 4.09 gears, mild 350/TH350 gets 12-13 highway, haven't checked city mileage but it's probably not too bad with the 4.09's.

[Carl Spangler]

My full sized 86 C10 with a 350ci and 350auto got around 10 MPG on a good day.

My current 71 C10 SWB with 250ci and 4 speed gets pretty decent gas mileage which equates to mid-high teens MPG. This 71 SWB truck is significantly lighter than the 86 and the little 250ci has a miserly single barrel carb.

cheers
JohnG

[Eddie H.]

My 69 GMC long bed with a 406 small block, TH400 trans and 3:08 gears : 11-12 MPG
My 2012 Silverado 2500 extended cab long bed with 6.0L and overdrive : 11-12 MPG

[CST10]

1970 LWB, 462 CI, mild build 425HP/480TQ, stock turbo 350 with lockup converter, 3:07 rear gears. Just went to Cruizin The Coast. Drove back roads there got 12mpg, in bumper to bumper traffic for hours got 6mpg, drove interstate home at 65 mph and got 12mpg. Not bad for a BBC.

[Dean'smeanmachine]

Originally Posted by Eddie H.

My 69 GMC long bed with a 406 small block, TH400 trans and 3:08 gears : 11-12 MPG
My 2012 Silverado 2500 extended cab long bed with 6.0L and overdrive : 11-12 MPG

love this statement!!!! people are always like " old trucks are worse on gas cuase there heavy, carburated, bla bla bla bla" a truck is a truck. it dosent matter if its feul injected or not. its a truck.

[tarafied1]

I have a 72 Cheyenne Super LWB 2WD 350/350 with 3.07 rear ratio. It has HEI conversion and a Holley 600 and dual exhaust, other than that it is stock. Around town I get about 8, my 16 year old son gets around 6 with the same truck (his right foot is heavier I guess).

[engineer_gregh]

BB 402 .30 over, fresh build with Comp Cam 268HE, HEI, turbo 400, headers, 3.07 open rear end, and 275x60x15 (28 inch tall tire) tach's just over 2400 RPM at 65 and averages 12 MPG on the highway, just under 10 in the city.

stock 307 2 barrel (tired), turbo 350, 3.07 read end, points, no headers, duals with flow masters, 275x60x15 gets a solid 15.5 highway and 12-13 around town.

Sustained RPM's matter. Here are some links to calculate what you will see based on tire size, rear end ratio, and speed. To the best of my knowledge our final transmission ratio
is 1:1.

http://tech.oldsgmail.com/axle_RPM.php
http://www.advanced-ev.com/Calculators/TireSize/

I used to know the actual formula but forgot it. All of it learned from this site. This is the best board I've ever been associated with, period.

[dmw319]

Just bumping this thread of mine for fun. I average 8-9 mpg. Not going to lie, I wish it was a little better. But I am also glad I live so close to work so it's not a big deal

[1972BlueC20]

I have a 1972 C20 with 4.10 rear gears and TH350 automatic.

It's got a brand new GM Crate engine 350 / 330 hp with 1000 miles on it.

Running an Edelbrock # 1406 carb (this one is supposed to be for economy)

I get a consistent 10-12 mpg regardless of driving....10 if only in city.....12 if a mixture of city and highway.


My old original 350 engine got pretty much the same.

[joeydurango]

Original setup: 4x4, 350/350, 3.73 - 10 mpg highway
New setup: 4x4, 5.3 LM7/4L60E, 3.73, 2.5" lift, 33" tires - 17-20 mpg highway (also way more fun)

[R.L.]

71 swb 250 3 sp. 4-10 rear= 14-15 mpg. I don't drive very hard.

[jimbosprint]

Originally Posted by 1972BlueC20

I have a 1972 C20 with 4.10 rear gears and TH350 automatic.

It's got a brand new GM Crate engine 350 / 330 hp with 1000 miles on it.

Running an Edelbrock # 1406 carb (this one is supposed to be for economy)

I get a consistent 10-12 mpg regardless of driving....10 if only in city.....12 if a mixture of city and highway.


My old original 350 engine got pretty much the same.

I have the exact same setup and I haven't gotten any better than 9.5mpg. I expected what you are getting.

[1972BlueC20]

Originally Posted by jimbosprint

I have the exact same setup and I haven't gotten any better than 9.5mpg. I expected what you are getting.

Is your vacuum advance hooked up? If so what port is your advance hooked up to?
what's your timing set at?

Are you running 93 octane?

[jimbosprint]

Originally Posted by 1972BlueC20

Is your vacuum advance hooked up? If so what port is your advance hooked up to?
what's your timing set at?

Are you running 93 octane?

I'll send you a PM so we don't derail this thread.

[mechanicalman]

Originally Posted by PAWS 72

350-.030 over-3.08 = 5-8 mpg 32 mile round trip running 50 to 60 mph.
Drove nearly 200 miles today to a car show and averaged about 14.6. Ran around 55 to 60 mph.why the big diffrence?
I bought a tach and it showing 2300rpm at 60 mph.Is that about rite for 3.08's?

Something might have been sticking, like power piston in the carb. Did you see any black tailpipe smoke the day of the 5-8 mpg?

Mechanical advance in the distributor. Was it sluggish that day?

If it was brakes they would have went up in smoke.

You might have gotten ripped off at the pump, volume wise if you used those numbers to calculate.

Could have been also atmospheric differences, altitude, air temperature, grade, headwind, etc.

Actually, 32 miles is not a good sample, a different gas pump might have kicked out differently when you topped it off. I'd guess the 14.6 on the 200 mile sample is lots more accurate and I would not worry about it until I did another long sample.

RPM's sound about right.

[dirtyjim]

around town I don't even try to figure it out but occasionally I do go a road trip and think I averaged around14, considering I'm running on a wore out 305 from a 84 Camaro with almost no compression in a couple cylinders I think I did ok.
the 700r4 definitely helps even around town

[imjeff]

396, T-400, 4x4, 3:73, 4" lift...6-8 mpg in town; no car payment in 15 years, priceless!

[Don Quixote]

350 .060 over, RV cam, oversized valves; SM465, 14bFF 3.73 = 11-13 without enclosed car hauler; 5-7 with enclosed car hauler.

I care not, the Army pays my loaded miles most of the time and I haven't had a payment since I bought it in 1997.

[Steeveedee]

400 BBC with a Q-Jet, 400 trans and 3.55 rear gears. Latest check was 9 in town, 13 on the highway. That shell is heavy and blocks wind. I recently converted to an HEI, but haven't checked it for mileage since then. I don't mind the 13 mpg on the road, but it has three fuel tanks, so it stings at the pump.