Hi every body.
First the stillen 3rd gen. will they help me ? cuz our weather is so hot .
Secound, Do i need headers ? and if i need what brand should i use for the g37 sedan ?
Third , does the coupe and sedan , have the same high flow cats , or they are different ? and what brand should i use ?

 

I live in a tropical weather all eyar round too, had an injen and i feel my car goes faster, although not significant, but i can feel a slight increase. Athough i had the air intake mostly because it looks better on my engine bay.
Not sure about headers.
Exhaust should be different too.

 

First the weather or tropical climate does not matter how the stillen will perform, that's a non-issue.
Second, headers are not that important and do not produce a strong enough value to gain, spend your money else where like a catback or somewhere else.
Third, HFCs are the same for the Coupe and Sedan, there are tons of good articles and even DIY's if you use the search function or scroll through the numbers of posts on this topic. Good luck.