[quote author=danielj link=topic=136663.msg2945691#msg2945691 date=1234995903]
I don't know why you would want to bother. The stock exhaust is so restrictive. If you're upgrading the header, why not follow through with a free flowing exhaust.
[/quote]
lc gained ~5whp, and more interesting, 10ft-lbs with a 4-1 header and the stock exhaust.
Link.
I wouldn't do it unless intending to get an exhaust eventually, but a header can work with the stock exhaust.