Gas Mileage
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
Team Owner
Joined: Jul 2008
Posts: 23,419
Likes: 22
From: In limbo
St. Jude Donor '13-'15, '17 thru '22
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.
BTW, to those adding av gas and the like: When I first got the car, it didn't seem to run right unless I added a couple of gallons of "Cam2" racing fuel to each tank. When I finally got the tune right (which took a lot of learning on my part, it was harder than tuning a VW engine ;-) ), I didn't need any kind of additive to the fuel anymore. It ripped better on pump premium then than it ever did on the Cam2. If your compression ratio is in the 10s or less, and your premium fuel is 91 octane or better and you need to add anything to the fuel, I think you would be better served by working on your tune than adding crap to your gas. Just one man's opinion.....
Pro
Joined: Feb 2009
Posts: 589
Likes: 1
From: PA
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
When's the last time it got new plugs, an air filter, distributor rotor and possibly distributor cap? It shouldn't need plug wires if it is a true 50,000 mile car. It's very hard to believe you're only getting 11 miles per gallon.
Thread Starter
Intermediate
Joined: Aug 2009
Posts: 30
Likes: 0
Gas Mileage
The car sat for six years in Miami and all the rubber rotted. The carburetor had to be rebuilt to make California smog and it wasn't running great.
Wonder if I should replace the dist cap, rotor, plugs, plug wires?
Other than a rough idle sometimes when at idle, the car runs great but... 11 miles SUCKS.
Thanks for thoughts, Greg
Wonder if I should replace the dist cap, rotor, plugs, plug wires?
Other than a rough idle sometimes when at idle, the car runs great but... 11 miles SUCKS.
Thanks for thoughts, Greg
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
The car sat for six years in Miami and all the rubber rotted. The carburetor had to be rebuilt to make California smog and it wasn't running great.
Wonder if I should replace the dist cap, rotor, plugs, plug wires?
Other than a rough idle sometimes when at idle, the car runs great but... 11 miles SUCKS.
Thanks for thoughts, Greg
Wonder if I should replace the dist cap, rotor, plugs, plug wires?
Other than a rough idle sometimes when at idle, the car runs great but... 11 miles SUCKS.
Thanks for thoughts, Greg
For the record. My carb is a BG Speed Demon 650 CFM. I replaced the jets (smaller than what was sent) and Power Valve.
Filled up the tank today. Drove around town, stop & go, a few stops for normal everyday stuff, and a short blast down the 4 lane highway. Went 18 miles total and the gas gage needle hasn't budged. I'm going to do some more cruising around and when the needle gets to the 3/4 full mark, I'll fill it back up and do the math.
I'll let you know what I get.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Pro
Joined: Feb 2009
Posts: 589
Likes: 1
From: PA
The car sat for six years in Miami and all the rubber rotted. The carburetor had to be rebuilt to make California smog and it wasn't running great.
Wonder if I should replace the dist cap, rotor, plugs, plug wires?
Other than a rough idle sometimes when at idle, the car runs great but... 11 miles SUCKS.
Thanks for thoughts, Greg
Wonder if I should replace the dist cap, rotor, plugs, plug wires?
Other than a rough idle sometimes when at idle, the car runs great but... 11 miles SUCKS.
Thanks for thoughts, Greg
I have to wonder maybe the previous owner put some lower gears in the back, maybe a cam and some other high performance parts inside the engine. Did you buy the car from a private owner or a car lot in Florida? The reason I ask is, a private owner would have told you what all has been done to it.
You said the car runs great, and that's great! Especially passing CA emissions. Maybe all we're going to get is 11, 12 mpg out of it. If that's the case well, just enjoy your Corvette and don't check gas mileage anymore.
Race Director
Joined: May 2003
Posts: 10,956
Likes: 409
From: California
BTW, to those adding av gas and the like: When I first got the car, it didn't seem to run right unless I added a couple of gallons of "Cam2" racing fuel to each tank. When I finally got the tune right (which took a lot of learning on my part, it was harder than tuning a VW engine ;-) ), I didn't need any kind of additive to the fuel anymore. It ripped better on pump premium then than it ever did on the Cam2. If your compression ratio is in the 10s or less, and your premium fuel is 91 octane or better and you need to add anything to the fuel, I think you would be better served by working on your tune than adding crap to your gas. Just one man's opinion.....
O, and BTW... ~ 3 weeks ago I was running a Edelbrock 750 getting ~13mpg, Just changed it to a BG Speed Demon 750 and now i am at less than 10mpg... and 15 more foot pounds of torque on the dyno...
Maybe I need to tap my own oil well...
Safety Car
Joined: Nov 2005
Posts: 3,961
Likes: 573
From: Lompoc, CA. Santa Barbara County
On the Holley Commander 950/4Di, you can adjust your accelarator pump shot. I have mine pretty maxed out to eliminate any bog. Maybe that is my culprit, but I should be getting better than 10-13mpg with fuel injection, headers, dual free flowing exhaust, and only 224/234 duration cam.
Bee Jay
Bee Jay
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
If it's been sitting for 6 years, it's gonna need a lot of things replaced.
For the record. My carb is a BG Speed Demon 650 CFM. I replaced the jets (smaller than what was sent) and Power Valve.
Filled up the tank today. Drove around town, stop & go, a few stops for normal everyday stuff, and a short blast down the 4 lane highway. Went 18 miles total and the gas gage needle hasn't budged. I'm going to do some more cruising around and when the needle gets to the 3/4 full mark, I'll fill it back up and do the math.
I'll let you know what I get.
For the record. My carb is a BG Speed Demon 650 CFM. I replaced the jets (smaller than what was sent) and Power Valve.
Filled up the tank today. Drove around town, stop & go, a few stops for normal everyday stuff, and a short blast down the 4 lane highway. Went 18 miles total and the gas gage needle hasn't budged. I'm going to do some more cruising around and when the needle gets to the 3/4 full mark, I'll fill it back up and do the math.
I'll let you know what I get.
Got, round off not up, 18mpg.
That's just my normal driving around, no coasting, no hot footing it either.
Really like to see what it'd do if it had a 4 speed OD.
