Currently have 103" and 57's with decatted headpipe. Looking at dynos, it seems the X pipe, or VH PD's, add ~5+ tq everywhere and move the power band left a few hundred rpm's, and right several hundred rpm's. Generally speaking, these headers increase the area under the curve quite a bit. Realizing mufflers also play a role, I will go with either crusher mellows or Fatshotz for both performance and to keep the noise down.

Can some one who first ran the stock header with cams, then later changed the header to either an X pipe or VH PD's, tell me what the sop difference was? Obvious, subtle, only better throttle response... It seems adding a performance header with cams is part of a good recipe. However, I have had some, including a reputable tuner, tell me its not worth the money and time. Even on a used header thats 60% off.

 

Lots of Dyno sheets show little difference but did my '09 in steps first Was basicly stock 103 with 54cams A/C, stock '09 non-cat header and fatshoz (19disc & open caps). Only change was fullsac header and I noticed way less heat plus a real midrange boost, 6th gear actually became useful under 70 on the freeway... Headwork and compression after that made a full package.

 

I have 2012 SG, 103 ", 57h cam, V&H pro pipe, cobra proflow air cleaner. Tuned with TTS tuner. Dyno turned out 102 torque, 93 HP. The medium baffle did better than the high proformance baffle. Needed a little back pressure I quess. Hope this helps you. I like it.