had this question asked recently, will find my answer.
The factory extractor type manifolds fitted the 3S-GE and BEAMS 3S-GE are very good. Toyota put some effort into the design and flow of these. So any gains, are not going to be as much.
-Edophus+
QUOTE (Edophus)
rusty is right, there isnt a lot wrong with the stock extractors... the welds tend to be tack welds on the outside and welded on the inside, if you reweld the manifold so the welds are on the outside of the pipe, take a dremel and grind out the garbage on the inside of the pipe, so far i've found the manifolds to be really sloppy here, the design is fundementally fine, but the execution is poor. This isnt a power adder as such but will free up the engine at high revs
I dont know if you've read it but
this thread has a lot of good infomation regarding the 3S-GE engines.