M K

iTrader: (9)

me and a mate were talking about the power/torque losses between dyno figures & rolling road figures,

have i heard correct that torque can not be measured as accurately on a roling road due to not being able to load the engine up fully??? where as on an engne dyno the load can be applied direct to flywheel ect?

but bhp is normally the same as it would be on a dyno?


any info appreciated

gus

iTrader: (1)

interested in this too

ECU Monitor Enthusiast

iTrader: (1)

None. Your question is flawed.


A dyno measures accurately the engines performance.

A rolling road can ONLY measure TORQUE which it converts to BHP
using run down friction losses/drag etc...

A rolling road is ONLY accurate if these losses are measured correctly
and the opetaor does his job properly.

(Dabbing the brakes during run down adds BHP)

Also, rolling roads unless they have an RPM lead connected to the engine
will not offer an accurate Torque/BHP/Rpm reading.

gus

iTrader: (1)

learn something new everyday

-beefy-

iTrader: (6)

so what ur saying is keep an eye on ur tail lights during the run down on ur rr session , to see if the operators having u over ??

ECU Monitor Enthusiast

iTrader: (1)

beefy-rst-2

Yes BUT, handbrakes dont put the brake lights on though

rapidcossie

it depends whats on the engine when its on the dyno...

air filter/exhaust etc.

dyno figs are generaly higher aswel as its easy to control inlet/water temps etc

vroooom ptssssh

SECS, Only really applies to 42wd/rwd cars, fwd you'd see the brake lights go on

M K

iTrader: (9)

so what will i see do you think on the rollers if on the engine dyno i saw 300bhp & 356lb/ft

or is it dependant on the type of roller used as well as operators method?



also i agree it will differ due to contolled parameters on the dyno such as act. water, oil ect

gus

iTrader: (1)

you will probably see you gearbox falling to bits

Tim

iTrader: (1)

i think you will loose 40 hp from what ive seen before,ie dingos on harvys dyno to rr etc etc.

GaryEvo

only if the dyno uses the coast down method not all dynos do!!

Anonymous

My Dynoed 504bhp made 399 on the RR & before you say the car was crap it held the then RWD Topspeed record at 183.3mph. MikeR made 398 from his 511bhp engine also a 180mph car so I rekon that the loss is 20% as these 2 examples show.
Rod

XRT_si

iTrader: (2)

But FWD losses are different to RWD losses? then again that must be quite marginal too.

foreigneRS

not quite. it converts torque at the rollers to power at the rollers using only the rotational speed of the rollers. nothing to do with losses unless you start talking about power at the wheels (losses through the tyres), power before the diff (losses through diff, driveshaft joints, wheel bearings, tyres etc), or power at the flywheeel (include any propshaft losses, gearbox losses etc)

as above, the torque figure at the rollers will almost always be relatively accurate, as it measured very simply using a load cell or similar. what may not be correct is the power calculated from it due to inaccuracies in the 'measurement' of the engine speed. it may not be as much torque as is produced on the road either, due to the load not being as high and airflow not being high enough to achieve the level of charge cooling seen on the road.

correct. most use the cars rev counter to set the engine revs at something like 4000 rpm which corresponds to a certain roller speed. the roller speed is then used in the calculation for power, so if the rev counter is inaccurate, everything else will be.

Chipped UK LTD

Many factors alter the final figure.

Tyre pressure
Wheel ballencing (on the drive wheels)
State of tyre
Make of tyre
Acceleration control

ECU Monitor Enthusiast

iTrader: (1)

So despite your deliberate attempt to discredit my statements,
I was actually correct.

foreigneRS

fuck off with the paranoia you twat

it's a discussion, i was pointing out some inaccuracies and omissions from your post for the benefit of other readers, nothing more.

didn't realise that you were an expert on dynamometers as well

ECU Monitor Enthusiast

iTrader: (1)

Ouch, did I touch a nerve there


What ever

Fiecos Dan

Also a engine dyno will have inaccuracy's that can be used to gain figures.

Also a engine in a cell, wont have all the extra's fitted like in a car.
eg, alternator, powersteering.


A proper RR, will be able to load a engine up fully, like a engine dyno.
And will be able to hold the engine at a set RPM, with full throttle,boost in use.

foreigneRS

quite right

most of the unreliability of the figures from a rolling road are due to the operator, not the equipment

OOG

Ah the good old can of worms labeled "Rolling Road Accuracy"

M K

iTrader: (9)

cheers or the info people,

will have to compare when i put it on some rollers at some point