How many more MPG can I expect from EFI on a 73 Charger? What does a typical EFI system go for?

ideally if you have a well tuned carb maybe 1-2mpg more. but in reality most carbs people pull out of the box and drop onto their engines, maybe swapping some jets, etc, but never get the tune really good with adjusting air bleeds etc. so in reality if your good at tuning the efi I wouldn't be surprised at 4-5 mpg increase or even more, depending on how you drive your car, how large the engine is, how good the engine is built etc. efi systems can get from 4-500 dollars build it yourself up to 3000+ for an all inclusive kit and some dyno tuning.

It is going to be based on what type of EFI system you buy. A plug and play (self learning) system...maybe 2 - 4 MPG, more if you drive conservable. If you get a tunable EFI and are good at tuning or have someone write you a tune then maybe 4-10 MPG. A lot will also depended on the motor you are running.

My system is a FAST ECU and F&B 6pac, 500 hp 440....I am averaging 8-10......but I have a difficult time keeping my foot of the Load Pedal. I could have it retuned and if I only drove on the center throttle body I probably would be in the 15 range......but what fun would that be.

On the W350, I can tell you TBI injection and an overdrive is good for about 6-7mpg on a 360 built for torque. Built the motor before, and with both the Thermobog and a Demon carb it was getting about 10-11. Typical of a truck with 4.10 gears of that era. Plenty of power, it would light all 4 tires up even at this altitude. After all the changes and some tuning it will pull 17mpg over 2 mountain passes gaining 6800' in altitude at 65mph. That's about as fast as she will go... I would say each one is worth 3mpg, but I don't have a baseline with only one change since they were both done at one time.

Going to a self tuning EFI system is no guarantee that your performance or your mileage will improve. There are a good number of threads on this subject and there are plenty of users that are not happy and some have even removed the EFI.

The difference in economy between your carb and EFI is totally dependent on the quality of the tune in the carb compared to the abilities of the EFI. And again, there is no guarantee that there would be any improvement with EFI over your carb.

Are there any complete EFI systems out there for less than $2,000 including the fuel pump and it's parts? And that is not including labor. Plus, the EFI can only do so much without tuning the ignition. But that is either a more expensive and complicated EFI system or more time and money to dial it in.

In a lot of cases it would seem to make more sense to get a competent carb tuner to select the correct carb for the application and tune the carb and ignition on a dyno for optimum economy. That would cost half the amount of the EFI and except for the starting procedure could well out perform many self tuning EFIs.

Back when most V8 powered trucks went from carb to sequential electronic fuel injection, most gained about 2 MPG in the the EPA Highway test.

But there was a trick with compression ratio at the same time.

Most carb equipped V8s would ping past 80% throttle in summertime heat on 87 octane AKI rating gasoline if the static compression ratio was over 8 to 8.5

With sequential multi-point fuel injection
most V8s got their static compression ratios raised to 8.9 to 9.5.
With the same 87 AKI regular gasoline this would have caused pinging past 80% throttle, but now with computer control the air to fuel ratio was greatly richened at above 80% throttle opening to ratios as rich as 10 to 1.
These very rich afr ratios surpress knocking,
slightly decrease peak horsepower about 3%
and greatly increase hydrocarbon pollution even with a catalytic converter.

Below 80% throttle daily driving fuel economy improves
due to the compression ratio increase (about 4%)
and due to less variation cylinder to cylinder ( about 6%)

Why oh why would the EPA allow all this increased HC pollution above 80% throttle?

Because for over 20 years Michigan Representative John Dingell used his position to keep a "Emergency Passing Power Exemption" in the EPA regulations.

Nancy Pelosi/Henry Waxman staged a coup against their fellow Democrat Dingell a few years ago and the regs are now different.

Note that every auto driving below 80% throttle got better MPG, less crude oil was imported, and less CO2 emitted.

Even higher compression ratios could have been used if water-methanol injection had been used above 80% throttle, instead of very rich AFR.

"Note that every auto driving below 80% throttle got better MPG, less crude oil was imported, and less CO2 emitted."


With all the research and development dollars spent on those platform specific systems and all they got was 2 MPG? So just how much improvement should you then expect a universal self tuning system to deliver?

Remember too, that they optimized the ignition for the application. I keep bringing that up because most self tuning EFIs do not control the ignition. And we all know that any fuel delivery system is dependent on the ignition to work at it's full potential.

Several years ago a US Congressional Committee hauled in the heads of the major automakers and made them testify under oath as to why the peak horsepower ratings of engines were increasing by a much larger percentage than the fuel efficiency.

All of the chief engineers testified that even with their best efforts they could not average better than 1% per year fuel economy improvement... with the current EPA pollution regs, particularly the NOx one. Toyota, BMW and Honda all said pretty much the same, not just GM and Ford.

Over ten years they were only getting a total of 7% improvement in engine fuel efficiency.

This was about 2004 or so and the 5.7 Hemi had just come out to replace the 1993 Magnum 5.9 V8.

The official Chrysler press release said that the 5.7 was
"six to twelve percent more fuel efficient"
than the Magnum 5.9 V8"
which I took to mean that the
5.7 was twelve percent more fuel efficient at full throttle peak torque,
and six percent more efficient at 55 mph highway cruise throttle setting.

A couple years after that i was shown how to access the EPA raw data MPG test databases by a guy in a coffee shop in Chapel Hill who worked at the EPA labs in RTP.

I compared the
2002 Ram Magnum 5.9/46RE/3.55
to the
2003 Ram 5.7 Hemi /3.55
and the new 5.7 was six percent better in the raw data Highway test numbers,
although part of that might have been due to
the new transmission
or the change in tire diameters,
or better rolling resistance in the OEM tires.

I have not checked how the Pentastar or Tigershark engines compare to those they replaced.

I wish that Chrysler would make public the BSFC graphs of older engines.

mileage is not the only thing being adjusted with efi. the quest for efi started due to lower emissions. lower emissions and fuel mileage don't go hand in hand. ultimately every engine manufacturer is fighting 3 things.

1. power
2. efficiency
3. emissions

the epa mandates that you tune for emissions, however horsepower sells, and fuel mileage is 3rd.

You will not get much more MPG than a freshly adjusted carb. That said, the continuous adjusting of the EFI will keep your engine in tune for a whole lot longer than your carb will so long term MPG will increase.
I love carbs and the challenge of getting them tuned for best performance. But the variation of gasoline formulas, the temperature variations of the seasons and just time in general mess up the settings. If you have an O2 sensor hooked up, you can watch it vary from day to day and gas tank to gas tank fill. With closed loop EFI that optimum tune lasts for a lot longer.
Craig

Original poster is listed as living in Los Angeles. I don't know what areas he drives in, but the stop and go city driving here gives you much different MPG than those living even in the suburbs of LA let alone less dense city or less dense suburb type driving.

I wonder if the benefits of EFI would be less in heavy metropolitan driving?

I have a work vehicle that I drive in metro LA and get 3-4 MPG difference than the same vehicles in Rural-City mix in Central CA and Riverside (city but much less dense). -Those MPG calcs are made filling the tank and recording the exact milage accurately in a log book.

A carb can not cut off the fuel during coasting like EFI can. It can not mix the fuel at lower speeds like EFI can unless you compromise higher speed flow. There are a lot more compromises with a carb.

One sutle advantage of sequential port EFI
is the design of the intake manifold can become
"dry air flow"
which allows intake runner designs that are longer
and plenum box volumes that "resonate" at lower RPMs,
or at two different RPMs
like the Dodge Ram 8L iron V10.

This boosts torque in the daily driving range
and allows more flexibility in gear ratios.

Another advantage that is not much used
is that each cylinder can have a slightly different capacity injector
to match slightly different runner air flow capacities.
This AFR fine tuning would be most valuable on
an economy engine running at a high 18 to 25 air to fuel ratio.
Going from 14.7 to 19 AFR would probably improve highway cruise by 2 MPG,
but then the exhaust would have too much NOx for current EPA regs.

Remember, too, that a carb has to be retuned for every weather change then tuned again for differences in altitude.


EFI is not a magic wand but it will generally improve the driving experience as well as fuel efficiency.

My current carburetor is a Carter AFB 4 barrel. I don't know how well it can be tuned. Yes, I'm in los Angeles, so lots of stop and go traffic. I know this will depend on a lot of things, but is there a rule of thumb as to how many miles you have to put on the car before an efi system has paid for itself?

We don't have such wild temperature swings here in L.A. so I'm guessing that 90% of the time I'll be driving the temperature will be in the 70s or 80s.

All this support for what EFI "is capable of". But in the real world after 60+ years of carbs and most guys don't even know how to size a power valve and then you're talking about dry intakes and sizing injectors. Get a grip!

A properly set-up and tuned EFI engine management system is the way to go. But is out of the reach (in more that one way) of most muscle car hobbyists.

The OP is interested in a plug and play self tuning system. For half the money, he can have a proper carb tuned and his ignition dialed in to his combo. Which would likely outperform an economy self tuning EFI kit. So let's compare apples to apples here.

And no one has quoted real world prices on a complete EFI system, have they? One with all the pieces needed for a real install. And then it is very possible that it will be a turd. Read the posts on here about these self tuning systems. There are more unhappy owners than happy.

EFI is probably the future. But here and now, they are expensive, changing constantly, and not quite ready for prime time. When they get their act together, I will have one on all my cars. But not today. Not yet, they're just not ready.

Let's be optimistic, given the following you would break even after 3yrs.

EFI cost: $2400
Yearly miles: 6000
Initial MPG: 10
EFI MPG: 15 (5 MPG improvement)
Gas cost: $4 per gallon

Gas cost carb: (6000/10) x 4 = $2400
Gas cost EFI: (6000/15) x 4 = $1600

So you would save $800 per year.

Cut your miles per year in 1/2 (3000), then its 6yrs
Cut improvement in 1/2 (2.5 mpg), then its 12yrs

Not a good return on investment

Wow, lots of discussion, or maybe I should say speculation posted, but no one has really answered the posters question. Has any of the posters actually bought and installed a self learning EFI on their muscle car or are they going on hear say and not actual experience. I have a 512 stroker in my street car. I was running a Quick Fuel 1050 on it with a MSD billet dizzy with only mechanical advance. The 1050 was dialed in using an O2 gauge. The car ran great, but as stated buy several posters, the tune went away with temperature swings. The 512 was getting around 9 to 10 mph with the 1050. Okay ibises for a well tuned 512. But let's face it if you build a stroker motor your really not very concerned with economy, which I am not.

Two months ago I got tired of chasing the tune and bought a Fast 2.0 EFI and installed it on the 512. Total cost was in the $2850 range. The Fast 2.0 is a throttle body EFI and it controls the ignition, as does the MSD Atomic EFI. MPG is now 13 MPG. Thats a Hugh improvement. My personal thoughts are the majority of the mileage increase is due to better ignition control. I went from 36 degrees total, all in at 2200 rpm to a full ignition curve that incorporates mechanical and vacuum advance. Timing at cruse is now set at 39 degrees and I'm considering increasing it to 42 degrees. I'm betting the mileage increases with the timing increase. The engine is happier and so am I.
My advice to the original poster is this. If you can afford the cost of the EFI and your car is mostly driven on the street, get the EFI. I hope this answered your question.