how do you convert a bhp at flywheel figure to bhp at wheels and visa-versa
Some say you can some say you need a rolling road
some say 15% some say 20%
Where is the pop corn
[Edited on 16/11/08 by jacko]
quote:
http://www.locostbuilders.co.uk/viewthread.php?tid=100272
quote:
Originally posted by jacko
Some say you can some say you need a rolling road
some say 15% some say 20%
we on rollers next sat and a few of us having a beer bet on wot it will put out
Looking at your photos 2.1 bike carbs
6500rpm i say 150 bhp at the fly wheel
if im right do i get a prezzie
ps where are you going for a r/road
good look
Jacko
[Edited on 16/11/08 by jacko]
Its not a percentage, well, the bulk of it it isnt. Also, the bulk of the losses are actaully in the road/wheel interface.
However its fairly well understood that for the sort of powers commonly run in cars its around 10-20% ish. maybe.
Daniel
engine spec as follows
2.1 pinto
stage 3 big valve polished ported gasflowed matched head
race spec electronic ignition with non vac dizzy and programable advance
cbr 900 carbs
stainless system matched to valve timings
regulated electric fuel pump
tarmac rally cam with 3400-7800ish power band
last time on rollers before bike carbs,ingnition and exhaust it made 136 at 3700 before flat spotting and cutting out so il be happy at 155
[Edited on 16/11/08 by tcr]
[Edited on 16/11/08 by tcr]
Unless you have an engine dyno - it's the power at the wheels that counts - the rest is just about bragging rights - in which case use 20% not
10% losses - in fact in your particular case use 30% - you will get much better flywheel figures that way 
Dont the RR operators have to enter certain factors for the software to give an indication of what the flywheel power is - hence where some of the confusion comes from. For me it i sthe wheels that apply the power to the road so that is the figure that is most relevant.
The rolling road guy I used said that transmission losses were not a percentage of enging power. Losses in propshafts, drive shafts and wheel
bearings are related to road speed. Similarly, losses in gearboxes and diffs are related to road speed as well as engine power.
If you tune up your engine by 10% at the flywheel, you will not increase the transmission losses by 10% if the peak power speed stays the same.
Lets say your car made 100 BHP at the flywheel at 120 MPH in top. Your transmission may lose 15 BHP, leaving you with 85 at the wheels. Now lets say
you tune up your engine giving 110 at the flywheel at the same engine speed. Your transmission losses my only go up to 15.5 BHP or so.
Tyre pressure makes a huge difference to the readings you'll get off a rolling road. An under-inflated tyre wedged on two rollers will make a huge loss