Is there a performance difference in the 98' ls header vs the 99' gsr? I know the a-pipe is different. I'm wondering if the ls header is hurting performance on my stock gsr. At a quick glance the top 4-2 section looks very similar.

 

Nope, if you had an LS header-catback it would be the same. There was only a difference in the type R.

Performance wise that is.... Geometrically.... I didn't think a 98 ls header would fit a 99 gsr, I thought the 99 gsr had a shorter header WITHOUT an o2 bung, so where would you put the o2 sensor that was previously there? Unless you took the LS cat along with it?

 

Yea, the 02 sensors would probably have to be lengthened. This car (98' DC4) has a 98' ls complete exhaust but with a 99' GSR engine. I've got the 99' gsr manifold and exhaust. I would just need a test pipe or cat from a 99' but sounds like it would be a pointless mod.