can anyone tell me what size injectors I should use to be good for 400 hp
5.0L ?

apparently the ones that came with my non-HO engine are only 14lbs/hr ???
they are grey

I'd be guessing 24lb or 30lb injectors.

Yes non HO's are 14lb.

You can get away with 24's on an efficient running 400hp engine but 30lb's are safer.

You can work it out yourself with the following formula;

HP=(Cyls x Inj size x Duty Cycle)/ BSFC

Where Cyls = number of them
Inj size = lb/hr
Duty cycle = % (eg .8 = 80%)
BSFC = Brake Specific Fuel Consumption (Default Normally aspirated = 0.5)

Example; (8 x 19lb/hr x .85)/ 0.5 = 258.4hp
Hence a good safety margin by the factory rating of 225hp for the 5.0L

You can rearrange this formula to achieve this;

Inj Size = [(HP x BSFC)/ Cyls]/Duty Cycle

Example; [(350 x 0.5)/8]/.85 = 25.73lb/hr

Pete.