Gas Mileage
Thread Starter
Intermediate
Joined: Aug 2009
Posts: 30
Likes: 0
Gas Mileage
I have an '81 Vette that has 50,000 miles on it with a newly rebuilt carburetor that runs really good. (it actually rough idles sometimes at idle - can't figure that out!)
But my great running car only gets 11 miles to the gallon. Am told this car should get 15 - 17 which would make a BIG difference.
What could this be? Do I need high end plugs, coil, wires?
The original gigantic catalytic converter was replaced long ago with a more streamlined model.
Would a new high end converter make the milage even better?
Any thoughts?
Thanks, Greg
But my great running car only gets 11 miles to the gallon. Am told this car should get 15 - 17 which would make a BIG difference.
What could this be? Do I need high end plugs, coil, wires?
The original gigantic catalytic converter was replaced long ago with a more streamlined model.
Would a new high end converter make the milage even better?
Any thoughts?
Thanks, Greg
Race Director
Joined: May 2003
Posts: 10,956
Likes: 409
From: California
Lol. I have been wanting to post this question ..... Or something like it.... When she was stock I was getting about 16+ out of a stock L-82 with a 4 speed (1979) but now it's a built 383 and I'm down to 10-11 mph prememum only + Avation gas mix in the hot months... And sometimes in the cold ones to...
But not to worry.... The repair bills will far and exceed any gas bill, and thus you will never worry about something so small !!!
But not to worry.... The repair bills will far and exceed any gas bill, and thus you will never worry about something so small !!!
Race Director
Joined: May 2007
Posts: 11,334
Likes: 136
From: Out of Site...Out of Mind. Corvette: anything else is just transportation.
St. Jude Donor '09 thru '20
Might be running to rich.
I put a new carb on my '75 and started getting "gallons per mile" instead of "miles per gallon".
Went to smaller jets in the primaries and a different power valve. The PV that was in it was the wrong size from the factory. Didn't realize it untill I had the float bowl off and happened to check it out and looked at the spec sheet for what was suppose to be in it.
Between the jets, and the PV, the carb was putting so much gas through it that my car was flooding out going down the road.
I put a new carb on my '75 and started getting "gallons per mile" instead of "miles per gallon".
Went to smaller jets in the primaries and a different power valve. The PV that was in it was the wrong size from the factory. Didn't realize it untill I had the float bowl off and happened to check it out and looked at the spec sheet for what was suppose to be in it.
Between the jets, and the PV, the carb was putting so much gas through it that my car was flooding out going down the road.
Le Mans Master
Joined: Jan 2003
Posts: 6,575
Likes: 1
From: Tuttle OK
Cruise-In VIII Veteran
Race Director
Joined: Oct 2000
Posts: 15,036
Likes: 79
From: central FL, near the beach.
G
back in 1980 i had a 76 that went to 17+ from 13 by adding true dual exhaust from a 68-72 w/turbo mufflers.
.
read how my 61 went from 11 to 18-19 mpg
http://community-2.webtv.net/MATTGRU/carb
mpg is your cars IQ
i had to send mine back to school!
i've improved the article quite a bit recently. Some guys got off track so i spelled things out more clearly, i hope
back in 1980 i had a 76 that went to 17+ from 13 by adding true dual exhaust from a 68-72 w/turbo mufflers.
.
read how my 61 went from 11 to 18-19 mpg
http://community-2.webtv.net/MATTGRU/carb
mpg is your cars IQ
i had to send mine back to school!
i've improved the article quite a bit recently. Some guys got off track so i spelled things out more clearly, i hope
Last edited by Matt Gruber; Oct 18, 2009 at 06:29 AM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Melting Slicks
Joined: Mar 2006
Posts: 2,465
Likes: 0
From: Orange Park Fl
Are you still running the original carb and computer?
If so, you cannot re-jet your E4ME carb, so forget that suggestion. The good news is, you should not have to, it is very efficient.
The first thing I would check is the exhaust system. Leaks at the headers or a restrictive/ clogged cat or muffler will destroy mileage.
If the computer is not working it will cause extreme richness (plug fouling). Also, the "Check Engine" light would be on (does it work?). I doubt that is the problem, these computers are pretty reliable, but if it is the problem, it is cheap and easy to replace.
I have spent many years getting to know the '81 CCC System. It is very good. Let me know what you find and we will get that car working correctly.
God bless, Sensei
If so, you cannot re-jet your E4ME carb, so forget that suggestion. The good news is, you should not have to, it is very efficient.
The first thing I would check is the exhaust system. Leaks at the headers or a restrictive/ clogged cat or muffler will destroy mileage.
If the computer is not working it will cause extreme richness (plug fouling). Also, the "Check Engine" light would be on (does it work?). I doubt that is the problem, these computers are pretty reliable, but if it is the problem, it is cheap and easy to replace.
I have spent many years getting to know the '81 CCC System. It is very good. Let me know what you find and we will get that car working correctly.
God bless, Sensei
Pro
Joined: Jan 2009
Posts: 576
Likes: 3
Matt, read your article.
Exactly the reason why I want to run an Offenhauser Dual Port intake on the engine that I want to build. Supposedly better mpg since it completely separates the primaries and the secondaries all the way to the intake port on the head.
Currently highway about 100 miles/quarter tank, 15mpg or so.
And that's with a bad cam and an old q-jet.
Exactly the reason why I want to run an Offenhauser Dual Port intake on the engine that I want to build. Supposedly better mpg since it completely separates the primaries and the secondaries all the way to the intake port on the head.
Currently highway about 100 miles/quarter tank, 15mpg or so.
And that's with a bad cam and an old q-jet.
Race Director
Joined: Oct 2000
Posts: 15,036
Likes: 79
From: central FL, near the beach.
Matt, read your article.
Exactly the reason why I want to run an Offenhauser Dual Port intake on the engine that I want to build. Supposedly better mpg since it completely separates the primaries and the secondaries all the way to the intake port on the head.
Currently highway about 100 miles/quarter tank, 15mpg or so.
And that's with a bad cam and an old q-jet.
Exactly the reason why I want to run an Offenhauser Dual Port intake on the engine that I want to build. Supposedly better mpg since it completely separates the primaries and the secondaries all the way to the intake port on the head.
Currently highway about 100 miles/quarter tank, 15mpg or so.
And that's with a bad cam and an old q-jet.
I suppose with a 218* cam it could run fine, up to maybe 300 hp. .
plenty of guys get hi-power & 20+ mpg at cruise, so it is safer to copy their combos.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The folks who get 20+ mpg on the highway with their C3's have: 1) crate engines with computers and injectors; 2) overdrive transmissions which cruise doing 70mph at 2000 rpm; 3) both computer/injection and overdrive trannies; 4) '81 or '82 C3's with properly functioning fuel metering systems. The rest of us carbureted folks are getting 16mpg or less at highway speeds.
Oh, I should have added another: 5) those who have converted their earlier C3 fuel systems to TBI or TPI injection.
Oh, I should have added another: 5) those who have converted their earlier C3 fuel systems to TBI or TPI injection.
Last edited by 7T1vette; Oct 18, 2009 at 10:24 AM.
Race Director
Joined: Oct 2000
Posts: 15,036
Likes: 79
From: central FL, near the beach.
there are carbed vettes that get really good mpg. often they have a q-jet or 4165/75 holley. A stick helps, or a locking converter. several guys claim 20-24, but i don't keep copies as everything is in the archives. I once had an automatic, stock, 67 318 cuda that got 25.9 on a long trip, so 20's are not pie in the sky.
Check th C2 section too! i tend to remember high HP cars:
i've seen enough reports of c2's 3.08-3.36 BB 427 w/tri power that get 15-16 to believe it.
Gkull has a 427 sb c3 that gets 17 at 100+mph.
do your research! plenty of good proven combos!
EFI is no longer needed for 20 mpg, but it is nice if you have got it!
Example,
What would i change on the 76 c3 that i had in 1980? At the time true duals gave a best of 17.6 mpg. it was almost stock otherwise. i had removed the caps on the idle screws, and had no idea at that time how important they were for mpg. So i'd turn them in 1/8 turn each week looking for more mpg. And it had only 8.5:1, pathetic
so i'd raise it to 10.5- 11:1 w/aluminum heads and a better cam. I can't go back in time and report the results, but it would improve for sure. More compression really helps mpg at cruise, and HP WOT.
Check th C2 section too! i tend to remember high HP cars:
i've seen enough reports of c2's 3.08-3.36 BB 427 w/tri power that get 15-16 to believe it.
Gkull has a 427 sb c3 that gets 17 at 100+mph.
do your research! plenty of good proven combos!
EFI is no longer needed for 20 mpg, but it is nice if you have got it!
Example,
What would i change on the 76 c3 that i had in 1980? At the time true duals gave a best of 17.6 mpg. it was almost stock otherwise. i had removed the caps on the idle screws, and had no idea at that time how important they were for mpg. So i'd turn them in 1/8 turn each week looking for more mpg. And it had only 8.5:1, pathetic
so i'd raise it to 10.5- 11:1 w/aluminum heads and a better cam. I can't go back in time and report the results, but it would improve for sure. More compression really helps mpg at cruise, and HP WOT.
Last edited by Matt Gruber; Oct 18, 2009 at 01:47 PM.
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
If the mixture solenoid is not working right, that can get the gas mileage.
Tuning is important.
Duals increase gas mileage & adding headers increases more.
Comp Cams says the 252H & 260H (good for 300+HP) cams will give more gas mileage than the stock cam.
Increase C/R.
Locking converters & O/D help on the hwy.
Tuning is important.
Duals increase gas mileage & adding headers increases more.
Comp Cams says the 252H & 260H (good for 300+HP) cams will give more gas mileage than the stock cam.
Increase C/R.
Locking converters & O/D help on the hwy.
Race Director
Joined: Jun 2000
Posts: 10,046
Likes: 675
From: FL
Drove my '75 cross country in 2001 with the 4 speed. 3000 rpm at 65 mph. Quadrajet, true duals, electric fans, and a bigger than stock (216@.050) cam. 20 mpg.
Now, with an even hotter motor, I still get 20 mpg but helped by having the Tremec OD.
Now, with an even hotter motor, I still get 20 mpg but helped by having the Tremec OD.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
A good way to save money is to reduce the idle down to a reasonable 450-550 RPM`s and to cut back on premium where its really not needed and just maybe about 90% of the engines here are under 10-1 compression and 87 will work. Racing fuel and Ave gas is really unnecessary in most Vettes. Over size carburetors with pumpers everywhere is another bad idea...Most could save money and get better mileage by merely using your head and dump those bragging rights parts most of which wont work on the street anyway....I`ve noticed that some are looking for performance and then do the worst thing possible to kill performance by looking for 2`s and super low 3`s in a gear ratio.....
And how much gas can you buy for the value of a 5 or 6 speed transmission? ......Put your money in what you see, not under the hood and enjoy the car. They actually can get good mileage if left alone...
And how much gas can you buy for the value of a 5 or 6 speed transmission? ......Put your money in what you see, not under the hood and enjoy the car. They actually can get good mileage if left alone...
