im running a ca18det with a few upgrades and have been browsing around for injectors some 444cc from a rb series motor i was told were suffiecient and plug rite in, but browsing around ebay and such ive seen some 720 and 550, is it ok to gothe extra mile and just tune them “lower” with a fuel controller, then if need be open them back up… just a thought 
thanx for any input
There was JUST a thread about this a few weeks ago, but yes, you can get outside the efficiency range on an injector by going too big. Usually just ends up with a really crummy spray pattern, and subsequently poor performance. If you need 444s, 550s might be ok, but 720s would be wayyy too overkill.
720s are only needed for some truly serious power.
If you only plan on making 250whp then even the 444ccs will be fine.
On the plus side you’ve got a CA meaning top-feed low-impedance injectors (peak and hold) which are a lot more resistant to the problems the SR20’s side-feed (saturated) injectors have when you go ‘too big’.
The peak and hold injector can open and close much faster than the saturated ones meaning finer fuel control so that you can run much larger injectors without going rich at idle.
injector sizing is just as important as turbo sizing. an injector is most efficient at around 70-85% duty cycle. before 70% its a bit laggy and over 85% its is being pushed to its limits.
here is an article from the sds website and a chart to match injectors
http://www.sdsefi.com/techffhp.htm
as you may know guys with serious horsepower and tuning run staged injection, this involves two fuel rails with diffferent sized injectors. this allows for fueling in the low to mid range and top range while maintaining a efficient injector duty cycle and spray pattern.
If you have a standalone EMS than you can adjust injector pulse width and you wont have any problems going with a bigger injector but if you are using a simply fuel controller and just pulling out fuel then the bigger you go the more complications you will have.
I have 740cc injector that idle and drive just like stock but I also run an EMS. What are you using to control fuel?
regardless whether you are using a standalone or a piggy back, an oversized injector will still be laggy and not efficient if its oversized. if you want to make 350whp a 550cc injector is perfect, but to use lets say a 750 or 850cc is overboard.
yes having room for more power down the road is good but you cannot change an injectors mechanical characteristics with a ecu.
As long as our duty cycle for a specific injector has the ability to stay within the 20% low to 80% ( 85% if disk style injector), high range, AT a min fuel press. of 38.6 psi at idle. Then use what ever you want… but doing a bit of math to size to your HP needs, makes for easier and cleaner tuning.
On a stock CA 750cc will NOT fall within that range at any idle below 900rpm.
This is all information available in the Bosch Fuel Injection & engine management text book.
im looking into the safc and a good boost cotroller… upgrading the maf, and having the computer reflashed…money is a partial issue so unfortunelty an ems unit is kinda dreamin at the moment 
im lokkin for around 250 rwhp give or take…
stock injectors then…