No Mods... Yet

Whats the cheapest way to get a '99 LS1 T/A to 400hp w/o messing with cams?

haha i think this is too open ended..

no cam job right? so how about opening up the internals?

Nitrous? Turbo? Super? you need some sort of forced induction if you want 400..

better ignition/injectors/pump
intake manifold/exhaust headers..
under drive pulleys..good for a couple..muffler? cold air intake? bigger exhaust pipes/cutouts.. @_@

etc etc etc

dude just get nos,exhaust,and a chip and you will be there.

supercharger maybe?

I agree with what everybody has allready said. The stock cams are pretty damn mild, so 400rwhp will require some major work.