It looks like someone makes a 4-1 header for the sentra
Its about $285 iirc. Here is the link.
http://www.headermania.com/mm5/merchant.mvc?Screen=PROD&Store_Code=H&Product_Code=5420&Category_Code=NISSAN4CYLHDRS
I cant tell what the collector size is and it looks to be made of mild steel but it does look much better than the ssac headers. They have cheap mandrel bends there as well.
http://www.headermania.com/mm5/merchant.mvc?Screen=PROD&Store_Code=H&Product_Code=5420&Category_Code=NISSAN4CYLHDRS
I cant tell what the collector size is and it looks to be made of mild steel but it does look much better than the ssac headers. They have cheap mandrel bends there as well.