AFter looking on some websites, i noticed that NO ONE makes headers for the maxima.....only y-pipes.

but why?

and if you buy a y-pipe, do you need to buy those y-pipe gasket sets and what do they do?

and how much hp does a Catman y-pipe give? and which is better, the catman one or the stillen one? i've noticed that the catman y-pipe is sold in more places

 

They don't differ in performance. Cattman uses better material which lasts longer. I planning on getting a Cattman y-pipe when I have the money.
Aren't the gaskets use to fill up the little gaps inbetween the pipes?

 

No one makes headers because they're expensive to R&D, but Don in Texas is working on it.

The Stillen y pipe comes with gaskets (but you have to make sure they send you all of them). Cattman does too, but I'm not positive on that.

Stillen and Cattman should give you around the same hp. The major difference between the two is Cattman's is made out of stainless steel, while Stillen's is ceramic coated.

 

If you look in the engine bay of the Maxima, you will see that there isn't a lot of extra space. That coupled with the R&D costs makes it difficult to design good, effective headers very easily. It will probably take a bit of work to do better than the stock headers.

 

And in CA/NLEV-spec Maximas, there's the thorny little issue of what to do about the front pre-cat. I don't expect anyone to come up with a cost-effective way to get rid of it, although some (Desert Pearl) are trying.