Umm lets clear a few things up.
In a most STOCK setups for medium/low powered cars, the 25- 30% ruling as fairly accurate, depending on all the variables that people have listed above. However, all this changes once your power figures go up....
Example: Generic V8 commodore... manual or auto, whatever.... 165kW flywheel, makes 125rwkW (its an example, dont question it!)
Loss is 40rwkW (24%), the car makes 166rwhp/125rwkW.... now, do something to improve its power output- stroker, blown, or similar.
So, lets say that the stock drivetrain can cope with 500rwhp without slipping (good box, clutch, diff etc). Car is now making 500 rwhp, which is 373rwkW.
A lot of people (even those i know, hardcore petrol heads included!) will tell me that their (example again!) 500rwhp car is making 500kW at the engine. However, 500kW is 680hp i say to them. So, your car is losing 180hp somewhere?? Ahhh, no its not.... you just like big numbers
Assuming your auto/manual/clutch/driveline etc isnt slipping and mashing itself, and you havent radically altered the wheel/tyre combos you shouldnt be losing anymore than the 40kW that was initially lost in the first place. Even if you put a bigger clutch setup in place, or rebuild your auto you wont be losing much more than a couple of kW/hp over a stock setup for efficiency, in most cases its better!
So, 373 + 40kW= 413kW @ engine. Yes, its 565hp, but its nowhere near the 680hp that some would claim....
The higher your power goes, the lower your driveline loss % becomes overall.... For the example above, the drivetrain loss is now
STOCK 40kW/165kW = 24% loss
MODIFIED 40kW/413kW = 9.6% loss
keep going with the power upgrades and the % keeps falling...
this kind of strange thinking has been around for years, i even heard several competitors at Summernats on the dyno (with hardcore cars) saying the same things- oh, i can make 800 rwhp, which is 800kW at the engine (1200hp+). Funnily enough, a lot of these cars (at the track) seem to run times and Mph like a lot of the other 850-900 FLYWHEEL hp cars...
Furthermore, i read an article online a while back where some guy had a "600kW" RB30 built for his VL turbo, and was expecting it to make around 600rwhp. Not surprisingly it made 725rwhp, even through a hi-stalled powerglide and 9" diff! That 800hp @ flywheel engine was losing 75hp (50kW) putting it to the wheels (built roller internals glide, alloy centre 9" diff etc), the guy even got onto the shop that built it saying they must have wound it up way past 600kW to get that!! They spent a while telling him how it works, explaining what the go was.
Confused? or enlightened?
Pls let me know if anything here needs clarifying
**VN Wagz**
