Hi guys would like to know are 570cc injectors to big for a ca18det,would like room for future upgrades.

i wouldnt have a clue... but they seem to be big for stock (arent stock more like 300cc? ) depends on the impedence of the stock injector to the larger mone, and what futre mods you plan and what tuning you going to do now to get these running. you got a fule pump that will supply enough for them too?

stock is 370cc im pretty sure. normal upgrade is 440cc gtr or gtir injectors

are you planning on running the larger injectors before you get these future mods? as that will require a different tune...which will be pointless if you are planning on doing futher modifications later which will require it to be tuned again

Hi guys im building a 300hp min engine that why i was thinking bigger injectors.

570cc would support up to about 210rwkw (280rwhp)

Firstly are you running an aftermarket ECu and what is it's abilities for resolution in ms.
When it comes to Injector sizing these days since the advent of the Bosch EV 14 Series and the modified versions available from such people as Injector Dynamics and Five0 Motorsport even a stock Honda Civic 1600 can run and idle with 1000cc Injectors,gone are the days of needing staged injectors such as used on the Ford Cosworth RS 500 Sierra.
Therefore when looking at injectors you can in many cases go for the size you are planning for future mods and use it on an earlier build spec engine sucessfully so only needing to buy one set of injectors for say a normally aspirated build that you plan to Turbo later.
These injectors will work very well with either engine spec so check out someone like Injector Dynamics for information,and when you actually talk to dyno operators with experience of them they will tell you just how nicely engines tune up on these injectors.
If you have never usewd them before I highly recommend checking them out as they really do work superbly.