drive train losses can usually be about, (READ """ABOUT""") 20% (ISH) it`s not a hard fact tho,,,
so at 100hp donk can see roughly 80hp at the wheels (ISH) (Roughly) (depending on how well its built & what other internal & external """grabby-ness""" there is (how`s that for a technical term """Grabby-ness"""

lucky it`s saturday or i`d have said "tightness"
very hard to acurately measure that sort of thing tho & then there`s also the torque factor... where a huge torquey donk may loose even more than the average donk through the drive train than a less grunty thing simply being due to the extra force into side loads through gears & thrusts from all that """MASSSIVE POWER""" crunching hard against side walls & thrusts & spreading gears apart & pushing hard onto the bearing sides etc etc etc
therefore, larger more hp motors do tend to loose more through the drive train than smaller more sedate & gentle donks
but anyone saying a "certain solid" % figure for drive train losses, really doesn`t understand what it`s all about. The rule of thumb for years & years has allways been bantered about at 30% for the average Joe Blow car,,,but hey,,,it`s just been a "Guestinmate"
people can easilly trick the rolling road dynos, buy doing things like fitting very narrow tyres with huge preasures , light wheel bearing grease & no pre-load & things like that,,,,
wide, sticky, low preasure tyres with poor wheel alignments & very tight wheel bearings & tight gearbox & drop gear clearances etc, will show a figure far less than realistic
get my point???
hee hee,,,,it`s all so easy-peasy when you think about it,,,,just very hard to "calculate exactly" ,,,that`s why there are things invented called "Engine dynos" as opposed to Rolling road dynos,,,both are good things to evaluate any changes tho, no matter what is chaned on either dyno, it should show up whether the change was good or bad,,,so in effect,,,the dynos are really only good for comparisons