whats up Im doin 390 injectors in my low compression engin je / eagle port polished blah blah blah

I hear all diff stuff about afcs not working some tiems it does soem times it doesnt? it either wors or it doesnt I dont get it whats the difference SAFC VS the SMFU? does it matter please give me all the info to help make m y decision

SFMU works off of vac. so as you increase boost you increase fuel pressure. So say you have a 9:1 plate for every 1 pound of boost you will increase your fuel pressure by 9. This is a good thing to have you can get many different plates all the way up to a 12:1.
A S-AFC works off the ECU and your sensors. Basically its inbetween the two. A S-AFC is good to have becuase you can fine tune your engine. What it does is increases or decrease voltage to your MAP sensors which increases fuel or decreases fuel.
Now a recommendation. I would do both. Well I am doing both. Make sure you dont have any CEL's as of now and youll be fine. But decide which plate to use on the FMU (Vortech says to do a 12:1) but you can email thme your specs and they will recommend one for you. Then with the SAFC you can fine tune what the FMU sees there for increasing your horsepower. But theonly way to do this properly is to either go to a dyno that has a sniffer or buy a wide band O2 sensor espscially if it has a digital read out like the LM-1. I hope this helped you out. I tried to stay as basic for you as could be done.

Here's the basic run down. SFMU is a fuel pressure regulaor. You will need this if boosting. It regulates the rise/rate of the fuel when under boost. A safc is an air/fuel controller. It fools the ecu to adjust air to fuel mixture, for fine tuning. Two different devices. That do two different jobs.