the m50 or s50 same manifold swap is a common m52 upgrade. it flows better than the stock manifold producing smoother power and more of it. the manifolds run about 100 bucks, then if you buy a 'swap kit' it's another 20 bucks or so in random parts to make it fit properly. took me and a buddy about two hours to do it on his car with a beer run half way threw (included in swap time).

for a chip you have a few options but i highly suggest the jim conforti software

when you do the manifold swap you can do something like a "cold air intake" if you want which will of course help with a little bit more power but mostly the sweet intake sound