A 450cc injector will be way too small for that kind of power. If you are worried about the cost of the properly sized injector, you seriously need to rethink this build because with 300 whp, there is a whole lot to go wrong if you continue buying cheap parts.

Anyways, I would go with somewhere in the range of 750cc or higher. Use this link to figure out which size you should be looking at: http://www.rceng.com/technical.htm#WORKSHEET