Fuel economy difference with efi?

[Beach Goat]

Hey everyone. Has anyone gone from a big-carb big block to one of the plug-and-play efi kits? And did you notice better fuel economy?

I specifically have a 580" wedge with a 1000cfm AED carb.

My car is in a weird zone, where it's power (725hp) is too low for the 4500 Dominator style holley kit rated for 800hp minimum, but I'm way too high for the 4150 kit rated for 600hp max.

What do you guys think?

 

[tonysrt]

I have a gen2 Hemi and had 2 4bbls before the F.I. and didn't notice any increase in fuel economy. I don't beat it up, only get on it once in a while. The only advantage was the better starting until the ECU crapped out.

 

[JimKueneman]

If the carb is setup right there will be little difference. Biggest difference it faster starting, no vapor lock, and wondering if you will be in cell service if the ECU or fuel pump craps out ;).... I went with a carb on my daughters Duster after the FiTech on the Coronet (no problems yet knock on wood but there are things that bother me with it) and question if I would do it again.

 

[1967coronet440]

You can use either the super sniper or 4500 Check out this thread from a while back. I’m in the same boat and I’ll be using the 4500.

https://www.forbbodiesonly.com/moparforum/threads/which-holley-efi.159489/

 

[kiwigtx]

Old MoPars, big blocks and fuel economy don't go together well in the same sentence.

Enjoy the cold starts, trouble-free hot starts, and the sweet smell of carpet in the garage after a cruise.

 

[Dennis H]

Pro Flo 4. Too soon to tell. In addition to the ease of use, I expect longer motor life due to running cleaner and not washed down with raw gas. No more soot on the tail either.

 

[BeepBeepRR]

I have installed 2 Sniper EFI master kits. Throttle response, ease of starting are all part of the deal. As far as gas mileage.. Its a big block like Kiwi says.. Plus they weigh bunch and running 3:55,3:91 etc etc isn't going to help gas mileage. 3:23 gears are bad enough..

 

[vance.dykes]

Pro Flo 4. Too soon to tell. In addition to the ease of use, I expect longer motor life due to running cleaner and not washed down with raw gas. No more soot on the tail either.

i like the pro flo 4 can you post pic's? what fuel pump did you use?how e-z was the first start set up ? any other problems or thoughts of install ?

 

[747mopar]

Like others are saying if the carb is tuned properly there will be little difference. A/F ratio doesn't care what it's coming from although EFI should keep it closer throughout the different transitions.

 

[PurpleBeeper]

Hey everyone. Has anyone gone from a big-carb big block to one of the plug-and-play efi kits? And did you notice better fuel economy?

I specifically have a 580" wedge with a 1000cfm AED carb.

My car is in a weird zone, where it's power (725hp) is too low for the 4500 Dominator style holley kit rated for 800hp minimum, but I'm way too high for the 4150 kit rated for 600hp max.

What do you guys think?

Ok, not answering your question, but what about a 6-pack setup??? If you have big ports, maybe one of those "rat roaster" intakes? On a 440 cid motor, I gained about 20% increase in gas mileage (as long as I keep my foot out of it). The car went from HORRIBLE to just crappy mileage

 

[1967coronet440]

The way it was explained to me, they both use 100lb/hr injectors the difference lies in the amount of air they flow, 800cfm compared to 1400. Bigger throttle plates etc, if your engine used a dominator carb and ran well you can use the 4500

 

[PurpleBeeper]

The way it was explained to me, they both use 100lb/hr injectors the difference lies in the amount of air they flow, 800cfm compared to 1400. Bigger throttle plates etc, if your engine used a dominator carb and ran well you can use the 4500

Well, at wide-open-throttle, assuming the engine could actually use the 1400cfm & the fuel mixture is correct for both throttle bodies & the injectors are not maxed out....yes, the 1400cfm would get worse mileage.
In general, fuel injection "should" get a little bit better mileage with the assumption that the computer/oxygen sensors are all working perfectly. It's because the fuel injection "should" keep the air/fuel mixture closer to perfect over the entire engine's rpm range. How much better? Not sure. Compared to a crappy carb just thrown on the engine, probably noticeably better. Compared to a well-tuned carburetor (idle, transition, mid-range, wide-open), probably not much. I have no first-hand data to back this up.

 

[66383]

I thought that's why we liked our old cars....no damn ECU to crap out!

 

[747mopar]

I thought that's why we liked our old cars....no damn ECU to crap out!

Amen brother, give me a wrench and screwdriver!

 

[Dennis H]

https://www.forbbodiesonly.com/moparforum/posts/911176676/

 

[Beach Goat]

Thanks guys. I've got the carb tuned very well, so it seems like I won't see a difference besides easier starting....not sure that's worth all the hassle of installing and tuning efi.

 

[Dennis H]

i like the pro flo 4 can you post pic's? what fuel pump did you use?how e-z was the first start set up ? any other problems or thoughts of install ?

i like the pro flo 4 can you post pic's? what fuel pump did you use?how e-z was the first start set up ? any other problems or thoughts of install ?

Edelbrock Pro Flo 4 best thing since buttered bread. Multi page thread on this here but can’t find it right now. First start up perfect.

 

[PurpleBeeper]

I thought that's why we liked our old cars....no damn ECU to crap out!

I agree + carburetors are faster on the top end of the drag strip. The main downside I see vs. newer car computers anyway, is that my newer cars "almost" tell you what's wrong with them through the computer(s). This is a God-send since they also have about 20 miles worth of wiring.

 

[idrivemopar]

If you have your carb dialed in, and your only concern is just cold starts, and fuel economy isn't going to be an improvement, then why not just spend a couple of bucks and install an electric fuel pump so you can prime your carb when cold to allow easy starts?

 

[1967coronet440]

725 horsepower stroker motors and fuel economy do not belong in the same sentence.