I get what you're saying and it's not a matter of 24s providing enough when combined with SD vs. MAF. Regardless of which induction type you're using, the fuel regulator is still vacuum operated. SD changes injector pulse-width based on vac while MAF performs that function based on volume of air ingested. I'm now running 24 lb injectors with my Kenne Bell but I'm also using an FMU to get the fuel pressure and volume to where it needs to be across the usable rpm range. Granted, I run more than 6 lbs of boost but data logging with my LM-1 wide-band tells the story.
As far as 24s working with SD, well... as I've said. Some cars take to it very well (mine did) but I've attempted the same in other cars that did not, regardless of what we did with fuel pressure etc. (go figure). Initially, the trick will be to see if you can get your specific car to run well on the 24s and THEN go about checking to see they will support your supercharger. 6lbs isn't a bunch but it's more than just a matter of whether they will support the peak power output but also whether fuel is being ramped in the appropriate places to get you the correct AFR across the entire operating range.
Tuning for SD can be accomplished through a TwEECer. There are also still some dyno shops out there that have the equipment and software to burn a chip for a SD computer (some are not even aware that they have this ability). The question then becomes one of cost. I'm not by any means telling you that you should convert although you should consider whether this is your final mod or if there are more in your future that will require significantly different fuel requirements. It's not a matter of whether it can be done with SD (because it can), it more a matter of the scarcity if aftermarket tunability for Ford SD.
Just to provide you with a little insight as to my current setup (so that you understand that I'm not trying to knock SD), it's as follows:
TFS heads (until very recently. Sold in order to help finance new motor build)
E-Cam (yes... E-cam)
Custom SD chip (allows me to run the cam)
24 lb injectors
2.2L Kenne Bell Blowzilla pushing 8-9 lbs
FMU 6:1
Adjustable Brass Vacuum valve (I purchased it at an aquarium store) I use this to finely adjust how quickly the FMU ramps up fuel pressure.
And most importantly!: An Innovative LM-1 Wide-band 02 meter.
With your setup, I'd say "Try it!" Just keep an eye fixed on your AFR so that you don't hurt anything. If you're dead set on keeping SD then start looking around for a place that is still able to burn you a chip. There are lots of places that still have the hardware. It's the software that's become very difficult to find. Regardless of that, you may still find that under boost, you'll need fuel pressures in excess of 40psi to support your blower at certain rpms while at others, elevated fuel pressure will cause you to run pig rich. Therein lies the necessity for the FMU.
I'm sorry that I'm not able to come in and tell you just what you want to hear but I'd hate to tell you something and have you hurt some portion of your combination. I've spent considerable time and effort making my combo work and it's more than just a matter of slapping in a set of 24 lb injectors. With MAF you can tune by electronic means. With SD, you will need to tune by mechanical means (if you're not able to somehow tweak electronically).
The new combo will not handle me running SD unless I rip out the Ford harness and computer and run something like the AEM system. $1800 for that thing and that doesn't include the wide-band option.
Look Ma! No meter!
Again, not trying to dissuade you. You many find another approach that will allow you get what you want without the use of an FMU. Whether it will be cost effective is another matter. Just trying to let you know what there is to look for when doing something like this. You run a totally different combo than I do that will have different requirements for air and fuel. You may get away with not running an FMU with 24s and boost. I wasn't able to. I am keeping in mind however, that boost from my combo is instant. That is something that is in your favor. What not in your favor is that to date: I've not seen any boosted apps with 24s that didn't need some sort of 'help' to meet the fuel demands without fuel inadequacy problems. It's not to say that they don't exist though. Good luck with your project!
