Rolling road formula for BHP from ATW reading?

[jonnyboy]

Whats the accepted way for working out your flywheel BHP from the @wheels readout you get on a rolling road?

 

[theduck]

there isnt one, from what i have read on here the lossbetween wheel and fly wheel varies from car to car, i seem to remember 17% being mentioned for 172/182's

 

[edde]

I'd go by the metod of ading 10hp for the wheel and then times by 1.1 to get flywheel.
However setting up on the rollers can affect the readings.
172's seem to make about 140 at the wheel and should be 166 at the fly.

 

[y0z2a]

168 @ the fly edde ;-)

/y0z

 

[Fred@BTM]

ring up the Labour party, and ask how they calculate their tax, similar princible can by applied to your question

 

[jimbo]

it depends on the rollers as much as it does the car, as said in a thread not so long ago by Andy from GDI, the place they use has an engine dyno AND rollers, and from the measurements taken on the dyno and then on the rollers with the same engine they have a fixed amount/percentage they use, as thats what most engines they measure stay true to

you can estimate with 17%, but its by no means an accurate representation. if its 1% out then thats a difference of maybe 1.5bhp or so, so unless its a big percentage off it will be fairly close, but not perfect

 

[Andy GDI]

RR losses inc tranny etc etc.

take RR figure add about 28% and you have close to fly figure.

std 182 does about 140 atw, and add 28% you get 179 bhp which is about right....

and yes we have tested this theory with the results from the dyno and then the engine in teh car and the figures are within 3 bhp .. so its pretty good...