Header Ciivic 1.5L ?

is it worth replacing my old cast iron exhaust manifold (176k miles) when I
do the head gasket with a header or will I introduce excess heat and noise?

 

I don't think that it will result in you having problems with your car in
the future. I subscribe to Honda Tuning magazine and have read dozens of
articles about people that have modified their Civic engines with headers,
turbos and all other sorts of modifications. If they can do it--you should
be able to do it.
You may want to visit their website:
www.hondatuningmagazine.com

The reason that I would NOT do it is related to cost. It cost lots and
lots of money to modify engines. It was obvious from reading some of those
articles that people develop obsessions related to modifications. One
person spent over ten thousand dollars on the modifications of his Civic.
It looked great but I wonder how his wife and children felt about his
spending so much time and money on the car instead of spending time and
money on them. If you just install a header--I don't believe that you are
obsessed and it may be a great investment if the old cast iron exhaust
manifold is in bad shape.