I'm looking to convert my 79' 400 to EFI.
Looked at the Holley Sniper 2300 which looks to be a good price and basically plug n play but I'm not married to it by any stretch, be interested to hear experience with other systems.
Curious if others have done such a conversion on a similar vehicle, how did it go, what gotchas did you run into etc? Specifically:

1. Do I need to swap out the fuel pump as well?
2. What else did you do along with the EFI? Any exhaust or header work? What about ignition? Higher compression would probably improve mpg too but that opens another can of worms, trying to keep it simple if I can.
3. What kind of gas mileage did you get post- conversion? Currently I can watch my fuel gauge go down as I drive, so anything would be an improvement but curious how much I can improve on the mileage?

thanks gang!

 

I've done an efi conversion on my Scout. Used a GM tbi kit. Pretty easy overall. Had to use an electric pump and run a return fuel line.
mileage is a little better than the carb, but efi really won't get better mileage than a properly tuned carb. Where the efi shines is cold starts and in the mountains with elevation and off camber situations.

 

I adapted Fox Mustang SEFI via a Lightning 351W lower and Price Motorsports adapters. Got rid of the distributor and went straight to EDIS8. Controlled via Ford EEC. Runs like a champ, can be submerged underwater and is dead reliable!

 

I have a 2300 style Sniper on the 300 I6 in my 85 Bronco. I absolutely love it.
It's good up to about 350hp, so unless you have a lot of power adders, it's going to be plenty.

Installation is straightforward, but not something you want to half do. Solid, quality wiring will go a long way.

Also, any EFI is going to be susceptible to intake/vacuum and exhaust leaks. A carb engine doesn't care about exhaust leaks, so lots of people who are converting to EFI don't know how leaky their exhaust is until the new EFI system doesn't run right.
Basically, any unmetered air that gets into the exhaust is going to touch the O2 sensor and make it think it's running lean, so the EFI will throw in extra fuel.
Make sure your system is sealed really tight.

And yes, you'll need a new fuel pump. The carb fuel pump is around 5 - 7 psi and the Sniper requires much higher pressure at around 60psi, so it won't run at all with your stock pump.
There are lots of aftermarket fuel pump setups you can go with, or you can get a Sniper kit that comes with a fuel kit.