I have a 454 30 over edelbrock top end kit with 10:1 compression it made 535 hp and 585 tq on a engine dyno with a carb. It runs fine in car with a carb but I have to warm it up for at least 5 min every morning ( yes I drive it everyday) and I'm calculating 8.35 mpg which makes me cry haha. So I'm thinking of going with the edelbrock proflo flo kit. But I'm not set to that. So would efi yield better performance drivability and milage?

Better drivability and starting for sure. Mileage depends on tuning and driving habits. After doing both carb and EFI on many different engines, I will always lean toward EFI.

Milage is kinda if it's better then good if not ok. But I am def looking for better driveabilty

Scott, what transmission and gears are you running? You would probably get more bang for your buck converting to an overdrive transmission. If you have a well tuned carb setup you may not see the kind of milage improvement with efi you might be expecting.

I second Magisnyc's advice. However I LOOOOVE my EFI on my 5.3. But it is a stock setup on a stock motor. I have sworn off Carbs. For the idea of saving money in better gas mileage: think of how much gas you could purchase for the price of the EFI setup, and how long it would take to pay for itself vs the cost of an over drive transmission built for your engine and how long it would take to pay itself off. BEST BET if you had the dough.. purchase both the OD trans and EFI... hand in hand.

I have a th400 and 3.55 gears I plan on swapping to 3.73s when I get my posi

Gonna drop the MPG's with that swap. Increase in the RPM = Degrease in MPG but more fun to drive.

Based on your HP/Tq numbers you have a fairly serious cam. I would guess you idle in the 10-12" of vacuum range?

An engine requires properly atomized fuel to run. A carb changes fuel from liquid to atomized state through a combination of factors and one of the biggest is pressure changes. With low vacuum there is no pressure change to use so fuel fails to atomize. Further the low speed circuits of a carb require manifold vacuum to pull fuel up out of the float bowl. And with a performance cam you don't have enough vacuum to pop a wet paper bag let along pull fuel. No fuel, poorly atomized fuel and engine stumbles. Sound familiar?

Once you have some heat it will evaporate fuel so at least the atomization gets better.

Now with EFI you always have a 40 PSI pressure change across the injector nozzle. This goes a long way towards atomizing the fuel right there. Then you have an electric pump pushing the fuel out so fuel is always delivered. Always delivered and atomized fuel means no more stumbles and a happy driver.

As to improving MPG... eliminating cold running problems will save you the 5 minute warm up in the morning. That will help. After that it depends greatly on how your carb is tuned and how your EFI gets tuned. The limit on leaning out the mixture is what your engine can take rather than how it is delivered. So you can tune a carb for just as good MPG as EFI (although most do not). How EFI gains the advantage is that you can tune it more specifically with less compromise between conditions than a carb. So you can run generally lean with EFI where a carb may only be lean under a particular set of operation conditions. Figure you might get 1-2 MPG advantage from EFI.

As previously pointed out however the biggest gains in MPG will result from reduction of RPMs at cruise. I picked up a good 2-3 MPG swapping from a Muncie to a TKO with 3.31 rear gears on my 402 powered El Camino. I now cruise under 2000 RPM doing 70+ instead of 2500 RPM at 60-65 MPH.