No way to tell from dyno. Period.
Only way to tell is with an engine dyno then a roller.
25% is the most commonly used number for mt 2.7t torsen, for example, but it's just a number, and has more to do with dyno variation and incentive to get big numbers than reality.
Anyone who tells you they know what number to use is lying. At the end of the day, only whp matters anyway.
The losses on a chassis dyno compared to an accurate engine dyno vary dramatically. Chassis to chassis dyno numbers can vary drastically for some valid and invalid reasons. The bottom line is that engine dyno tuning is the only true power data if the data is collected properly on an accurate dyno with properly input data. Unfortunately there is no accurate means to convert dyno data based on engine dyno power without accurate driveline losses or reverse calculate true engine power from chassis dyno data.
