In my few weeks of occasional research and browsing I have found a number of useful performance mods for the late model 4.2 supercharged motors that come in the "R" trim. Looking over some of the parts that i have found that upgrading the exhaust and induction systems are highly productive but i cant find very many dyno graphs to prove my theory. Now in looking at the design of the exhaust headers and from my past endeavors with supercharged motors (esp. high comp. V8's) this seems like a pivotal point in unleashing the true nature of the beast. My question to all of you is in your experience what is the "most popular" and most enjoyable simple bolt-on (by this i mean not having to dig into the internals) ?

 

although I say 4.2 motors any supercharged jag motor applies to this question really