my stock bore, stroke, iron block, iron head, single 4bbl, 9.1 compression hemi was dynoed with and without headers. 498 hp with manifolds, 511 with 3" headers. Already had 2.5" TTI exhaust from the former 440, so cutting up a new exhaust and dropping a $1000 on good coated headers just wasn't justifiable for 13 more hp. I also didn't mess with my starter or beat up my inner fenders like I have in the past with headers. Also, all the manifold cars i've ever had have never ran hot. All my header cars get a little warm for my taste and have ended up some type of leak.