i have 03 chevy with 5.3 i got tr224 cam and ls6 intake and full exhaust that all i have what else i need to reach 4

 

more cubic inches.
run a shot of NOS.
turbo or supercharger.

 

you may hit high 300's with FULL boltons, a bigger cam, heads, and some tiny tires, but no one has hit 400 rwhp with a 5.3L(to my knowledge). The highest official on that I've seen is 340

 

you really need a 6.0 to hit 400rwhp NA

a 6.0 will take FULL boltons, nice sized cam and probably heads and/or ls6 intake or better to hit 400 NA

i agree with all else that has been said

 

Well, you didn't say if you wanted 400 flywheel or 400 rwhp.

400 flywheel...I would imagine you are pretty close if you have a tune and full bolt ons.

But I also agree with the others 400rwhp would be forced induction, more cubes, etc.

 

I hit 304rwhp with a cam, tune, but I was running 22's which hurt me on the dyno. Changed to 20's. also headers ory and heads and a new tune and hit 355rwhp. Went with a radix after that......and still not done yet. So more cubes or FI is a must for 400rwhp.

 

ain't happening unless you use a shot of nitrous.

 

Someone's gonna do it, or at least try to.

 

Closet Red Neck may be close but I don't think he's dyno'ed yet.

 

I have a 228R and Stage 2.5 TSP heads. I am looking into every bolt on imaginable and possibly a t56.