As mentioned there are a lot of variables to consider. Even so, when I'm looking for a ballpark estimate I use 15% loss for manual transmissions and 20% for automatics.
If a car makes 400rwhp for example, I do the math like this:
manual....400/.85 = 470 engine hp
auto........400/.8 = 500 engine hp
again just an estimate
I'd like to see engine dyno's instead of factory numbers, but the
Factory ratings turn out like this, all over the map.
Dynojet 224 inertia testing.
Jeep srt8. 420 rated flwhp auto
Sae rear 367 = .87
78 Ramcharger 440 auto
220 fwhp
121 wheel =.55
Srt10 ram auto
500fwhp sae
360 rwhp=.72
Ferrari 355 challenge manual.
Rated 375 fw
290 rear wheel=.77
