are s4 headers and s5's the same? my problem is i got reffed in the wonderful state of california and i passed smog with flying colors, but i couldn't get my certificate cause i don't have a "carb legal" header. i have a buddy with a bone stock 88 gtu and was wondering if i could swap into my 89 gtu

 

The car comes with an exhaust manifold from the factory [a big chunk of metal with 3 interconnected holes], to swap that onto your car that has headers would probably require the precats and the manifold to be swapped. This is assuming you have the stock cat, or a stock length cat.

If you don't have a stock length cat, you'll have to swap the manifold, precats and main cat.

Of course.. This is assuming your catback is stock length...