What size injectors will I need to hit the mid 400HP mark???

 

try the injector calculator @ http://www.rceng.com

 

ide go with 720's...they will be plenty big with some room for more power...are you gonna run a standalone? if so you can prolly even get away with a little bigger injectors (like 850's) and still have no negative side effects as far as idle and such as long as you have a good tuner

 

I also agree. 720's will enable u to reach 450whp. On 550's I was around 90% duty cycle at the 400whp mark.