400+ Hp 5.3 Natural Aspiration

[Blackz715.3]

i have a 5.3 with a custom exhaust, intake, headers, and a custom tune. Im barely breaking 350 HP. you will have to get cam, springs, valves, and headers to get close to 400 HP

[Spurshot]

You need to find a reputable engine builder.

[Low14]

I'm at 398rwhp and I have a baby cam fbo so you will definitely need a cam and it's all on the setup and the tuning