I'm not diggin thru the attic for the book, -5% performance = - the headache of blown header gaskets, - the pain in the *** to replace starter motor, - the cost of mini starter to avoid that, - the steering linkage issues and all the other things, although I have headers on my duster and none of them issues, if I didnt have the headers layin around I would have used the 340 hp manifolds as I have done in the past.......Just Sayin :happy1: