I've long contemplated an EFI upgrade on a few of my cars, but the cost is still a good bit more than a new carb. I can't see saving enough fuel to justify over $1000.00+ in expenses.
Computerized EFI will optimize the fuel mixture for best performance. It can cure many ills of an ill-tuned carb/intake/cam combination, I suspect. I suspect that THAT will be where most of the fuel economy increase comes from. BUT if you set the mixture parameters too rich, no real savings might result. The optimum fuel mixture is 14.7:1 for non-ethanol fuels. Probably needs to be more like 14.1:1 with E10. Cruise air/fuel, that is. Idle will need to be lower, possibly.
One thing needed for the self-learning EFI is a compatible distributor! More costs not in the kit. Although some can control ignition timing internally. Something else to consider.
When the speed limit changed to 55mph, nationally, I was keeping tight figures of highway mpg, using % of throttle, rpm, air/fuel ratio, and such to figure each segment of my 290 mile trips home from college, circa 1973-4. The car was a stock '66 Newport Town Sedan 383, with a 1970 OEM Holley 2210 carb. 55mph segments came out to be right at 20 mpg. 2.76 axle ratio/H78-14 tires. Later higher speed limit trips dropped to about 17mpg. Before that, when newer, the highway mpg average (70mph speed limits) was about 17mpg. Local town stuff was more like 14mpg.
During the fuel crisis related lower speed limits of the earlier 1970s, Fenner-Tubbs Chrysler in Lubbock took cars in their new car demo fleet on a mileage check. They filled the tanks at the Shell station across the street from the dealership, then took the cars south to the edge of the Caprock, turned around, came back, and topped off the tanks. 1974 NY 440, 20.66mpg, Newport 400 2bbl, 20.33, GFury 360, 19.6. When I put a "matched" TQuad/Torker383 on the same '66 Newport 383, allegedly calibrated for a '70 383 4bbl, never got past about 15mpg highway, no matter what, or with different primary rods (from the TQ Strip Kit) I tried, seeking to match the '74 fuel curve). More perf, but no real fuel economy advantage over the earlier 2bbl.
To me, in reality, electronic EFI is just a better fuel-mixer than a carb can be. Performance happens as soon as the throttle is opened, not after the opened throttle results in increased air flow through the carb. That is where the better throttle response probably comes from.
Key thing about carbs is that it can be hard to really know the ultimate-supplied air/fuel ratio without putting the vehicle on a chassis dyno. A 13:1 ration can seem to be a 14.8:1 (stoich), when it really isn't, for example. Many like to "jet rich" for allegedly best performance, but this takes a toll on cruise mpg, as can deeper rear axle ratios and such. That "out of the box" carb might install and run well, but is it really as optimum as it could be for your car? With fewer techs really knowing how to work on carbs, probably best to have something under the hood they at least understand. Not that they'd know how the particular EFI system works of is calibrated.
The other place where electronic EFI is better is in the "coast" mode, where the factory units basically shut-down fuel delivery when it isn't needed. A carb can't really do that to result in the OEM EFI "coast" of 99mpg.
EFI will be MORE critical to driving style, by observation. Each time the EFI throttle is opened, more fuel into the air flow happens, no matter what. On a carb, when the throttle is opened, it takes increased air flow through the carb to get fuel from the float bowl into the throttle bores. UNTIL you get into a newer car with a readout of "Instant Fuel Economy", then watch it as you drive, you don't understand how critical throttle input is into the fuel economy delivered by the vehicle. It's all there in front of you, in real time. A 20mpg 60mph steady-state cruise can instantaneously become an 11mpg acceleration with not much added throttle, or when going up a hill with the cruise working. I strongly recommend this, even if you have to rent a car to do it. Quite revealing!
The referenced Chevy 454 pickups did get that mpg, from the factory. With a 4.10 gear, they'd "work", but they were thirsty. No black smoke from the exhaust pipes (from a too-rich mixture), either! Ford 460s were similar in similar vehicles.
So, the self-learning EFI can be a good thing to do for many people. Can save some fuel, too, in some cases, just don't expect miracles for the money spent.
CBODY67
