What kind of fuel mileage is every one getting

[dwcsr]

I'm at 11-12 city , hiway or towing, dosen't seem to matter.

[GKsport67]

bout 10 to 12 miles per gallon i suppose. i have a 327 with a mild cam. it cost me $30 to go bout 70/80 miles

[junkyardjohn]

AH... GAS MILAGE & HORSEPOWER.. IT SEEMS LIKE NO ONE UNDER ESTIMATES EITHER ONE. JOHN

[dwaite72lnghrn]

My 72 c30 402/th400, 4.11, with 30" 9.50x16.5 tires, weighs 5300lbs got 11.5mpg around town short trips. Best fuel "economy" was 14.3 on a few trips where it was all highway at 55mph tail gate down. The 502 in it now gets about the same.
A quick check of your speedo/odo is to get on a road with measured miles and mark your odometer reading when you pass a mile post, Run 10 miles and mark your odometer reading and the mile post. If you OD is 10 then you are good. For every tenth off is a 1% difference, If your OD is 9 miles you have a 10% error in your reading If it is 9.9miles you are off buy 1%. The more miles you can run the more accurate it will be.

[mstrav1973]

I am still waiting for the straight 6 guys with the manual transmissions to chime in on this. My bet is if anybody is getting in the 20's it would be them. I would need at least 4 or 5 of them to claim in the 20's to buy off on it.


Lets keep this one going as I am real curious about this.

Matt

[piecesparts]

Originally Posted by molinehotrod

I have 420 hp, 32 inch rear tire, 3.08 gears, 700r4 with 30% lower first gear and a taller over drive gear, i think it is .67. I think i am going to get 23- 25 miles per gallon.

I kind of doubt your calculations. I support this with the changes we did to my son's truck and the losses that we noted as we tried to get things straightened out. First of all, the 3.08 gears and a 700R4 tranny, along with a 32" tire is really going for a bad "Power curve" on your truck. Your acceleration from the stop lights will be hard on your engine. Using some basic math formulas, your RPMs on the highway at 70 MPH will put you at just over 1500 RPM. That sounds great, until you figure in any hills or traffic conditions. Then the attempts to regain highway speeds will eat up your gas mileage.

On my Son's 86 Chevy truck, we put in a 700 R4 with the 3.08 gears and a set of 27" tires and he lost 4 MPG. To gain that back we went to a 3.73 geared rear end and now the mileage is back to where it was originally. We could have stopped at a 3.42 rear end, but the lower gearing was desirable for street acceleration and also so that his cruise control would work in our area. You would be best to shoot for an RPM around 1900 to 2200 at 70 MPH.

[Longhorn Man]

most ppl on here claim 10 - 12 MPG. I did a poll quite a whiloe ago on this.
http://67-72chevytrucks.com/vboard/s...d.php?t=172346

Don't hold your breath on what you expect. In all reality, that sounds like an 8 MPG truck to me.

[special-K]

Who ever did the math on this original claim forgot to ever mention what motor is doing this...kinda left the important part out.420 hp what?It`s like government statistics,focus on this/neglect to mention that.I imagine this mystery motor would get 35-40 mpg in a 2500# aerodynamic car.Better call Detroit and get a job.We need you.

[americanmusc1e]

Originally Posted by cdowns

i think the overdrive tranny with those 308's you'll find not so good // you might get 14-15mpg

true........I have a '70 LWB with a 400hp 383, 700r4 and 3.08 rear with 30" tires.....I'm getting 10mpg

420hp usually means having an engine with a peaky power curve and they don't do well with with low gears.

[Scott Webster]

On a sunny day and not fighting the wind, I'd say I'm lucky to get 10-12 mpg on the highway. However, i'm usually playing around town and driving like I stole it. When it's low I dump more gas in. Previous owner of the engine bored it out to 355 ci., stock heads with bigger stainless valves, combo kit from Edelbrock (cam, intake, etc) Holley 750 cfm, and it's higher compression. Unless it breaks down, I'm not looking inside. Someday I'll give it a transmission it deserves, but for now it's a farmtruckish-4speed.

[67ChevyRedneck]

350/700R/3.73. 11-12 riding around town (If I have a "fun" tank, it drops to 10 ) I can push 15-16 highway. I just got done with a 300+ mile round trip, almost all highway, 15.2mpg.


Back when the truck was a 250 I6/3spd manual/3.73 I got 10-11mpg no matter what I did... but I also had a leaky carb...

But yes, these damn things are a brick. When you can "feel" the air fighting you at 60-70mph...

[ShredSled]

yeah, maybe something else to think about other than already mentioned is that cruising at 70mph speeds at only ~1500rpm, your trans is going to be constantly downshifting and upshifting, even on the smallest of hills or changes in speed/wind resistance. Not only will that be horrible for your gas mileage, it'll be hell on that trans!





...also find it interesting how many people seem to directly connect horsepower numbers to mpg results...

[Shyguy]

I had a bone stock '72 C-20 and it seemed no matter what I did it got 10 mpg.

I am not sure what the setup I have now in my '71 will get. When it had a stock 350 with an old style 4 speed, 3.73 gears and 31 inch tires it got in the 12-14 mpg range running at 55 on the interstate. Now it has everything the same except for a stock '73 454 with an RV cam.

Danny

[Bishops Trucks]

8 to 10 on my '71 K10 with a 330 HP rate motor. My '70 Z28 gets much better milage than the truck.

[Big69C20 Toy]

69 C20 2wd, 572 CID BB on 87 octane, 4.10 eaton rear, TH400, never dyno'd but computer dyno put it ~650hp/600ft-lbs

[87fleetsidedude]

i used to get 18 on a good day...thats with stock 305/700r4 and 3:43 gears...im not sure what i get now..after i put duals on i cant keep my foot out of it =P...

[mrein3]

Originally Posted by Stocker

It's simple -- combine your three most recent tankfuls. When you fill up, add that one to your calculations and drop your oldest of the previous three. This helps minimize the inconsistencies and give you a more accurate consumption figure.

Combining your last three or more is a good way to remove inconsistancies in how full you got your tank. If you always stop when the pump "clicks", that "Full" mark as defined by the mechanism in the handle might be different than the handle next to it.

FWIW, I just happened to fill my tanks yesterday. First time since 12/6/09. Remember my truck stays off the salt but does plow my driveway and makes numerous runs across the lake to the fish house. Fish house runs are usually 20 mintues of warm up time on the engine followed by .5 to 1.25 miles one way. Shut down. Warm up for 20 minutes or so, and run back home across the lake for .5 to 1.25 miles.

With that in mind my last tank was 3.7 miles to the gallon. Not my worst winter tank full since I bought the truck in 1994 but close.

Another thing to consider is who you get your fuel from. My daily driver gets lots of miles. 20,000 to 24,000 per year. I ALWAYS get 2-3 mpg better from the local BP station in my daily driver than I do from the local Holiday station. There are other places to purchase gas locally but Holiday and BP are my easiest places to stop at. Once you get a good baseline for your fuel mileage data, don't be afraid to try other suppliers to see if something is different.

I don't work for BP, Holiday, or any other gasoline company.

[Longhorn Man]

mrein3... you may want to stay away from the BP fuel in your late model GM. While nothing has been proven that I have seen, the fleets we work on that use BP fuel, tend to go through more electric fuel pumps that the fleets that use other brands of fuel.

[mstrav1973]

Originally Posted by Big69C20 Toy

69 C20 2wd, 572 CID BB on 87 octane, 4.10 eaton rear, TH400, never dyno'd but computer dyno put it ~650hp/600ft-lbs

you didnt tell us your MPG. what is it?

Matt

[pokerflatoutcast]

my 72 4 speed 3.73 stock 350 edelbrock 268 cam and intake and carb, lifted 6 in. and only 33's. only does around 9 mpg. at 60 mph. i wish it did better! I bet being so tall doesn't help it at all. i plan on taking the lift off and going to a nv 4500 tranny to get better milage. Seems to me that's the best way to get better mpg with these trucks. Lower the rpm at cruising speed.

[71longbed-brew]

Originally Posted by 71meangreenc10

These trucks werent designed to get high mileage, I get about 10-12ish around town with the 350/350 3.08's, my speedo is about five miles off........you might get 20 if everything was made of fiberglass, but again with todays light made trucks and fuel injection they are barely getting 20 and thats after 40+ years of technology and thats a 2wd auto with od......I dont mind the gas cost because there is NO car payment involved.

Smitty

i couldnt agree more with this statement

i'f you even remotely care about gas mileage ... you shouldn't be driving a classic truck .... i drive it for many reasons .. and MPG's isn't anywhere on the list

[67ChevyRedneck]

That's not true, at least not for everyone. I prefer a well tuned 350 with 7ooR to a high HP big block with a 3 speed. Some guys say they only get 8-9mpg, I'm very happy that's not me. I'm happy with what my truck gets now

"Better" fuel mileage = more money for more cruising

[Cole Trickle]

I just got around 13mpg at freeway speeds bringing the truck home from UT.

69 Short fleet 350/4 speed manual

[XwalkerX]

im going to bump this thread cause the comments are pretty funny.

all these members are telling the OP he is crazy but I just picked up my truck in Oklahoma and drove 1500 miles to SoCal while getting 22mpg

ive got an l33/4l60e swap with a 3.07 rear end

[piecesparts]

Originally Posted by XwalkerX

im going to bump this thread cause the comments are pretty funny.

all these members are telling the OP he is crazy but I just picked up my truck in Oklahoma and drove 1500 miles to SoCal while getting 22mpg

ive got an l33/4l60e swap with a 3.07 rear end

Just so you know, your engine combo is slightly (Hell Greatly) different than the OP. Just an observation. So what is the fuel system on yours like?