Ok..i bought my corvette a week ago and a friend had to drive it from where i bought it (100 miles) today, back to my home-town since i had to leave to come back to texas to deploy. Ok...before i thought it had 36k miles from what i had heard from my friend who told me about his father n law having it, i forgot to check it when i test drove..oops . Neways, it actually has 16k on the clock..he drove it the 100 miles home and had to fill it up halfway lol, he said it was getting like 6mpg? i can't vouch for the mileage myself, but i'm sure he was pretty close, and he was going 70-75 the whole way, 350/400 combo. 6mpg is horribly low for a car this low...i have NO idea what was done to the engine, as the PO doesnt even know, as he bought it like that, it ran like a dream....hauled ***, idled perfect, etc..didn't sound like it needed a tuneup. Is there anything in particular that would take it from the 15ish range to 6mpg? I'll be able to have my friend check on things at home....i'm hoping i can get it up to at least 10, it ran really strong, but i have NO idea what's done to it....no idea if it's stock or built up....even built up it should at LEAST get 10mpgish? It's light as hell and aerodynamic

 

I would normally agree with you. If you have a TH350 with 4.11 gears and a BIG engine then I could see getting those gas mileages when on the interstate doing 75. Did he tell you what the tach was at while cruising? Any other specs on the car? I agree that 6 is pretty low...but their are people here online getting less.

 

Was there air in the tires...

 

no idea on rear gear ratio....havn't had time to check it...they came in 4.11 stock rears? pretty low gear! My 95 fullsize bronco had 3.55 stock with a 302HO ...definitly low end torque


And..the tach isn't functional right now...either a cable or the sending unit is messed up, dunno for sure what's wrong with it...so, no idea on tach...


And, the tires are brand new, not super wide or anything to be heating up a bunch, and they wer aired up..they've had 400 miles in the last 4 years...and, my friend that drove is a main manager at Peerless Tires (decent sized tire chain) so if the tires did go flat, i could get free ones neways

 

My 69 502 4 speed gets 8-10.....3.70 rears...
Could be speedo is off a tad..

 

hole in the gas tank

 

When i ran it it didn't smell like gas too bad when i started it up in the garage..then i ran it around for like 25 min or so then returned it..did'nt smell like gas bad? and..didn't notice any puddling or anything? do these normally rust out bad? i'd imagine these don't have a skidplate like alot of trucks..so it should be driping down on the ground?

 

Years ago I had a 70 elcamino with the stock 300 horse 350, automatic, and 3.08 gears. It only got 12 mpg when I bought it and it turned out the vacuum advance diaphram was bad. I replaced it and it bumped it up to 18 mpg. Might wanna check that.

Mike

 

I know nothing about chevy engines, and nothing about carburated engines (i own a 95 bronco with 302 EFI, 96 PSD, etc)..i'm assuming this 350 also has a vacuum advance diaphram? i'll be checking into things...buying a haynes manual, etc..so i can get to know these engines better, i'm completely oblivious to things

Also..just talked to my friend, and..he said that it actually got 8-10mpg. and it might still be stock, he wasnt for sure...he said it was 6mpg because my mom was going to drive it tonight and he wanted to make sure she kept her foot out of it

Thanks for the info, i'll be trying to improve the power a bit and get better gas mileage on it cheaply if i can

edit:btw, it's a '75 if it matters, and..is there any smog/emission/little things you can do to bring up the HP on these engines, besides the normal plugs/wires/tune carb?

 

8-10 mpg ??? Funny...I get 8 if driving the 69 alone...10 if wife is along..

 

 

Rich, I'll call your 8-10 with my 6-7mpg........69 427 4 speed.....4.11 rears.......on AV gas.

Good thing I drive RamJet (TKO 500 with 3.08) the most.

Bullshark

 

OK...you said it was a Turbo 400 tranny....Put it in DRIVE and stop running down the interstate in 1.
You gotta put it in DRIVE!

Just kidding.... .....but you do have ISSUES.

Probably just needs a proper rebuild on the Q-Jet.

My 350 ran great ...idled great....but blew raw fuel out the
exhaust just at idle or going down the road. I about shut down
the drive through at Wendys. People were passing out from
the gas fumes.
The exhaust tips were sooty black.
A good rebuild on the carb
and now it has light gray ash exhaust tips and doesn't suffocate
every one behind me.

My 72 base 350/T400 gets 16 mpg no matter what.
My 74 Big Block gets 14 mpg even when airborn!

Start with the carb....good luck............44B

 

Your car set alot and ran little. This can do bad things to gaskets, fluids, hoses, etc. You'll just have to start checking everything. A lot of people buy these cars and go blasting out, only to have major problems. Take your time and check it out real good. Change fluids, adjust what you can, replace what you must, then enjoy. I think you'll at least double your 6mpg when you get it running well.

 

Probably running rich. Get a wide band O2 sensor and tune your carb. It will pay for itself in just a few fill ups.

This is of course assuming you have checked your compression and timing.

 

That thing must be running rich check the plugs...
sounds like its time for some new stuff under the hood!
Rebuild the carb,check the timing check all vacuum hoses..
change the plugs and airfilter also.....

 

I was on a club trip some years ago with my '78. Once guy had a '75 with a 4.11 rear end. The C5s were getting about 33-34 mpg, mine about 18mpg, and the guy with the 75 was getting about 8-10mpg at best. He would shout for gas, I would be at 1/2 tank, the C5s would be at 3/4. We started comparing rpms and the C5s were about 1800, mine about 3000 and his was aroun 4200 at 70-75 mph.

 

I'll get the tach working again so i can have a reference to things...the C5's seriously get 33-34mpg? what do the C6's get...and, i may be needing a C5 for a DD, damn! haha