471 BB 682 hp on dyno--in car made 587 hp at the tire with a TKO 5 spd,,,Did a 360 with Eddy heads small cam made 402 hp and in car made 312 @ tire. J.Rob
Your anecdotes seem right sub 20% for manuals and mid-low 20s for Autos
471BB+6speed--14% drivetrain loss. Sounds right for a MANUAL
360--22% drivetrain loss Sounds right for a Auto
But the OPs supposed 34% drivetrain loss seems a bit off as long as its not an automatic 4x4.
Doesn't matter if its +/- 20hp. Headers and intake will be a damn good upgrade especially in $$/hp.