I believe someone said to assume 20% power loss between flywheel and RWHP.

Just curious if someone has details on what this covers. Exhaust, PS, fan, alt, exhaust, air cleaner, A/C, heat, tranny, differential...what all is covered and are there aproximations for each.

The exhaust, fan, PS, air cleaner, AC and heat would affect the flywheel power and would not be part of the drivetrain losses. Only the transmission, driveshaft and rear axle would contribute to the drivetrain losses.