Yeah, the 316 and 318's are 8v, its the 318is thats the 16v, early ones are 1.8 and later are the 1.9 as used in the e46.

id have thought the exhaust will fit all the way upto the downpipe, this is where i think you could have problems. If the Exhaust manifold is the same fixing and same loction then it will obviously fit. or is it a cat back system???? the best thing to do is check something like a Bosal catalogue online and check part numbers etc

http://www.bosalna.com/index.php?mod=catalog - For the 318 i

http://www.bosalna.com/index.php?mod=catalog - For the 318 is

So as you can see they are the very same.

Hope this helps