My C6 Tranny for my 390 FE, in my 69 Mach 1 is needing a rebuild.  My question is how much horse power am I giving up with the C6 compared to a C4, TKO500, a T5, a 4 speed top loader, or a street/strip preped C6?  Has anyone ever compared the horse power differences on a chassis dyno? I know that the C6 absorbs quite a few horses, but how many or how much more that a manual trans or a C4? Can a hot C6 rebuild free up any horses? I rebuilt the engine and has been chassis dynoed to about 300hp. What can I expect in the real world after a new tranny?  

Here's a thread on that: http://www.network54.com/Forum/119419/thread/1051282664/

"Found an old July, 1991 issue of Hot Rod that references hp loss for all major trans types. Data provided by Torque Convertors, Inc. more commonly known as TCI."

Transmission - HP Loss
Powerglide - 18
TH350 - 36
TH400 - 44
Ford C6 - 55-60
Ford C4 - 28
Chrysler A904 - 25
Chrysler 727 - 45