xkeots

I have been using my 77 lately for the first time in years as my every day car as I am moving and this is my only New York transport till I am totally in Florida. Is 9 miles a gallon normal? I love this car and it is killing me that I put over 10 grand into it but I have to sell it as I have no room in new house. I kept my 62 convertible/HT, 63 SWC and 67 GTO convertible.
I just want to tell buyer that is it or it can get better mileage.
Thanks
Jack

pmr2000

Probably about right...I know for a '75 L-48 the EPA estimates was 10 city, 15 hwy.

So far in my rural Sunday type driving on a stock L-48, 80k miles I'm getting 10 mpg!

zrc3john

Well those three other cars your keeping should soften the blow when the 77 is gone..

I have a worked 350 in mine with a 370 gear with a 750 CFM carb..I know the feeling of lousy gas mileage .....Its just a pleasure car..The mileage your getting sounds right ..

Could be worse..I remember back about ten years ago gas was over four dollars a gallon for high test...

i remember being in the Hamptons about eight years ago and I stopped at a local station in Sag Harbor......4.75 a gallon !!!! I'm like this sucks....Lol....

revitup

9MPG sounds really low. My '77 L-82 is pretty much all original or original configuration replacement and I'm getting about 13MPG around town no matter how I drive it. The one lengthy highway trip I took where I checked the mileage, I got about 17.

NewbVetteGuy

You can certainly get more than 9mpg out if it.

The TH350 and big gears will definitely hold you back, though if you're doing highway driving. An EFI even a TBI EFI can help considerably and keep the mixture lean for the majority of driving conditions.

A 4 speed swap with a lockup TC or lower rear gears will help the most.


Many of the same mods that increase performance will continue making incremental improvement in fuel economy too: weight savings & reducing accessory drag; tires would be one place where performance and fuel economy are definitely opposed, though. Headers, especially race-style 4-2-1 stepped headers help with MPG, tuned exhaust lengths, improving your CR (head gasket leaking? -replace it with an ultra thin one that ups your CR by 0.5 CR points!).

Reducing engine friction also not only improves performance, but increases MPG: roller cam, true roller rockers, if you're getting a new rotating assembly 6" rods, coated (friction reducing and thermal insulating) parts, the newest generation of thin weight trans fluids with friction modifiers, etc...

For highway driving- reducing drag can net some small returns- pace car / Daytona front and rear spoilers, lower it!





If you're starting @ 9mpg, significant improvement is easy.

IMHO, the strategy for weight reduction and MPG improvement should be very similar: simply remain always cognizant of it anytime you replace anything- you can "kill" your bad fuel economy with "a death of a thousand papercuts".

I think I'm one of the very few people on here who cares about fuel economy in their C3, but for me, my vision is about the modernization of my 79 L82 and that encompasses not just an improved driving experience (perf+handling+steering) and new technology, but also improved fuel economy. I see people like BeeJay who have kept a laser-focus on their vision over a decade or more and their car just slowly transforms into that vision; I absolutely think the fuel economy will come in the same way; slow, steady progress over time.



Adam

LS4 PILOT

thats worse than my 454 ....LOL.....but I have manual and 3:36 axle.11-14 is about normal depending on driving habits .

i had 79 L82 12-17 was average .

you using ethanol gas .....that hurts

7t9l82

Ethanol fuel is hurting you.. a performance tune up like Lars specs will help a bunch. Do you still have that crappy catalytic converter? If so get Florida plate and have a real exhaust system put in.you should get between 15 &18 mpg with real gas

jb78L-82

Yes that is low....when my totally stock 78 L-82 4 speed 3.70 gears was new I still have the record of 12 MPG being the worse and 17 mpg the best for a tank...with 255/60/15 tires no less...the wider tires increase the rolling resistance.

The engine today with no emissions, Holley 4175 Q jet replacement carb, rebuilt 355 with roller cam, roller tipped rockers, 10.2:1 compression, headers, 2.5 inch duals, AFR aluminum heads and considerable weight reduction over the last 30 years does about 14 mpg city and 17-18 MPG highway with 425+ Gross HP...amazing..with a .64 OD 5/6 speed, I am sure that 22-23 MPG highway would be very attainable.

Most of the mileage gains on cars today are due to the same factors mentioned above: mainly weight reduction, port fuel injection, and much by just drastically reducing the engine RPM'S. Think about this fact that my daughters 2001 Pontiac Grand Prix weighing 3,600 pounds with a 3.1 V6 injected with 190 HP with a 4 speed auto with 200,000 miles on it turns 2,000 RPM @ 75-80 mph on the highway and has achieved 30 MPG....the car is 17 years old. My 10 C6Z06 with 505 NET HP turns 1,800 RPM with the aluminum SB 427 and gets 28 MPG @ 80 MPH...yes it weighs 3,100 LBS but most of the mileage is from the low revs.

holley505

LOL... I switched to a LS motor picked up ALOT more power and maybe 1-2 mpg... still get about 11-12 maybe...if I can keep my foot out of it.

pmr2000

Yikes that must be some beastly LS engine if you only get 11-12mpg!


My stock C5 got high teens to upper 20's think it was 16/24 EPA MPG rating.

SwampeastMike

That does sound low. My '79 L82 with 52k gets about 15 mph mixed to include some spirited driving. All factory emission controls except the catalytic converter are installed and functioning. Nearly new (< 2000 miles) plugs, wires, rotor, etc. with all of the vacuum hoses recently replaced. The caps are still on the idle mixture screws and other than my cleaning with carb/choke spray the carburetor seems untouched.