Fuel injection vs carb
Thread Starter
Intermediate
Joined: Sep 2018
Posts: 33
Likes: 1
Fuel injection vs carb
I know this subject has been talked about a lot. Right now I have a 75 with a ZZ4 and running a Street Demon 650 carb. I'm getting around 10mpg and wondering if going to EFI would help much on the fuel mileage? Not my daily but if I want to take the miss on a day cruise it gets a little ridiculous. TIA
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Even with you 373 and 3 speed auto you could do better than 10mpg if it's tuned well.
I get 19 mpg with a th350 355 gears and 440 hp.
The qjet can get really good gas mileage, it's what I run. But I imagine your current carb could do better as well.
I get 19 mpg with a th350 355 gears and 440 hp.
The qjet can get really good gas mileage, it's what I run. But I imagine your current carb could do better as well.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Burning Brakes
Joined: May 2017
Posts: 774
Likes: 375
From: Seattle WA
I know this subject has been talked about a lot. Right now I have a 75 with a ZZ4 and running a Street Demon 650 carb. I'm getting around 10mpg and wondering if going to EFI would help much on the fuel mileage? Not my daily but if I want to take the miss on a day cruise it gets a little ridiculous. TIA
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
It may be more than just carb tune affecting your mileage. Timing if retarded or not using a vac advance can ,can be a real fuel waster.
Drawing under hood air vs cold air can also waste fuel,
Drawing under hood air vs cold air can also waste fuel,
Last edited by REELAV8R; Jun 18, 2019 at 11:45 AM.
Race Director
Joined: May 2006
Posts: 18,710
Likes: 2,574
how did you end up with a 650? The engine comes from GM with a 770 Holley vacuum secondary.
https://www.hotrod.com/articles/hrdp...hevy-bolt-ons/
https://www.hotrod.com/articles/hrdp...hevy-bolt-ons/
Last edited by MelWff; Jun 18, 2019 at 11:53 AM.
Melting Slicks
Joined: Oct 2003
Posts: 2,175
Likes: 822
From: Chapel Hill NC
2025 c3 ('68-'73) of the Year Finalist - Unmodified
2025 C4 of the Year Finalist - Unmodified
2025 C8 Stingray of the Year Finalist - Unmodified
Instructor
Joined: Apr 2011
Posts: 161
Likes: 17
From: NW CT
I think they set many of the "ready to run" carbs like the street Demon really rich to make sure the customer has no problems with stumbling or pinging when they bolt them on.
I bet you could find a few MPG with a wideband and vacuum gauge.
I don't like aftermarket gauges so on my cars I have an O2 bung with a plug. When I am tuning I remove the plug and install the wideband O2 sensor that goes to an AEM gauge that plugs in to the cig lighter and just sits on my pass seat. When I am done I remove the whole mess and reinstall the plug in the O2 bung.
What do your plugs look like? Pull a few after a long drive and check them out. All black or clean and tan?
I bet you could find a few MPG with a wideband and vacuum gauge.
I don't like aftermarket gauges so on my cars I have an O2 bung with a plug. When I am tuning I remove the plug and install the wideband O2 sensor that goes to an AEM gauge that plugs in to the cig lighter and just sits on my pass seat. When I am done I remove the whole mess and reinstall the plug in the O2 bung.
What do your plugs look like? Pull a few after a long drive and check them out. All black or clean and tan?
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
A "hot air intake" reduces the actual amount of air in the engine and then with a properly calibrated carb or efi to those hot temps == less fuel. Hot air = less power, but increased MPG.
Adam
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
Very recent and relevant video from Finnegan's garage:
Took his giant 89 GMC Sierra 454 BBC truck towing rig and fixed the retarded ignition timing, installed new spark plugs, and swapped the TH400 for a 4L80e and went from 5.5 mpg to high 8mpg - low 9 mpg.
OD transmission with lockup TC, get some good ignition timing, run the cam a couple of degrees advanced, and long-tube headers for improving fuel economy. IMHO, the benefit of EFI is keeping it tuned, and if you go with ignition control and a knock sensor, being able to run the timing and cruise AFR ("lean cruise") on the ragged edge of detonation to get as much torque at your cruise RPM as you can. -You just can't be safely as aggressive with the ignition timing and running the AFRs lean with a carb or EFI without a knock sensor.
Adam
Took his giant 89 GMC Sierra 454 BBC truck towing rig and fixed the retarded ignition timing, installed new spark plugs, and swapped the TH400 for a 4L80e and went from 5.5 mpg to high 8mpg - low 9 mpg.
OD transmission with lockup TC, get some good ignition timing, run the cam a couple of degrees advanced, and long-tube headers for improving fuel economy. IMHO, the benefit of EFI is keeping it tuned, and if you go with ignition control and a knock sensor, being able to run the timing and cruise AFR ("lean cruise") on the ragged edge of detonation to get as much torque at your cruise RPM as you can. -You just can't be safely as aggressive with the ignition timing and running the AFRs lean with a carb or EFI without a knock sensor.
Adam