I've tuned hundreds of engines over 20 years, EFI and Carb

If somebody with a perfectly running carb engine approaches me to install and tune a generic EFI system I will generally talk them out of the EFI and to keep the carb.

Carb is far simpler, and more difficult to tune properly. The only thing that can really replace a carb that is worth the effort is a fully MPFI-SEQ-EFI with coil over plug ignition and injector phase capability. And even then it costs much more to install and tune (I am very expensive) than simply installing a late model LS engine which can support far more power, economy, reliability, than anything made before 2002 in Chevrolet world.

You can get a complete LM7 5.3L LS Gen3 engine for $500~ and it will support 700 to 800bhp for 200,000 to 350,000 miles if properly cared for. Factory MPFI-Coil over plug ECU is $50 from a junkyard and I can squeeze 25mpg out of a 650rwhp setup with 4l80e and almost 30mpg from a 6-speed setup at 3200lbs vehicle weight using $50 computer with no concern over reliability, oil leaking, longevity of components, etc... its basically crazy to try and keep the old SBC style engine in place, far inferior to a modern 02+ LS engine.

 

I agree with the wiring comment 100% - you need to run new power leads, you need proper splices into the stuff you do splice into. I'm talking solder and heat shrink. People try to do it fast and put a little 1 cent vampire splice on their tach wire and wonder why the system cuts out over they go over a bump.

I have the FiTech system on mine and it runs like a dream with better MPG and reliability over the carb. Yes, the carb was old and that was part of it, but why buy a new carb when the price of the TBI kits are nearing the same price? There's nothing worse than planning on going for a drive and find that the ethanol ate trough your bowl gasket again or some other BS.

 

If you have good wiring and tuning skills, and intent to drive the vehicle 8k to 12k miles per year, ditching a perfectly good running carb in place of EFI is not such a bad idea. Just for the sake of having the ability to adjust fuel and timing quickly without getting your hands dirty its not such a bad thing to upgrade to on any engine in any format.

However, you generally won't see a return in terms of fuel economy that pays you back for the initial investment.
And in terms of cold starts I can get adequate cold start performance from a carb by using a choke and a vacuum hose leading into the driver seat with a bolt plugged the hole, simply remove the bolt and choke the carb and walaa it starts up perfect in the cold. Replace the bolt once engine warms up. Its like a piece of chewing gum that renders $9999 of equipment useless.

So really not much benefit there to the switch from carb to efi. Other than you can now adjust EFI on the fly from the driver seat with a laptop to account for new modifications over time. Which is good if you constant mod your engine and drive alot to see the benefits in the long term.

power wise the carb and wet flow manifold based EFI is going to be the same. EFI offers very little advantage to a properly tuned carb if any.
The tiny advantage for EFI in air density power is when using a dry flow manifold. Air is more dense without the fuel component in a dry manifold which can add a couple percentage of power and air density to the airflow. But again that dry manifold and MPFI-SEQ efi system is found in all cheap truck engines 02+ LS style manifold systems using $50 ecu so I question the expensive aftermarket systems necessity over a few percentage of power.

Without the great tuning and wiring skills it is absolutely a no brainer to keep the carb. Paying somebody like me to set all that up perfectly just to replicate what the carb was doing is kind of crazy save your money