These discussions can be fun, but understand that trusting one dyno number is a stretch, let alone two. Let's pretend for a minute that the engine dyno is correct. Big assumption. Then you go to a Dynojet chassis dyno. Then you go to a Mustang dyno. Without a doubt those two chassis dynos will have very different results. People will debate all day long which is correct. The difference is easily enough to be the 15% or 20% loss difference. Now add the variability between engine dynos (i.e. a lot of happy dynos out there) and it really becomes a bit meaningless IMO. Said differently, you're trying to determine if the power loss is 15, 16, 17, 18, 19, or 20%. But you're tools for measuring power can be off 5% themselves.
Dynos are tuning devices. You really should not look at it as anything more.
FWIW, from engine dyno to chassis dyno, my 508 power loss was 20.5%.
The only numbers that matter to me are 11.68 @ 120.2 mph and 4150#. You want to call it 200 hp, I really don't care. 10% loss or 25% loss, I don't care. You call it 600 hp, I call you nuts.
