Hello all,

Had my car rolling roaded last month (see "view my Impreza"). The measured figure at the wheels at Dastek was 258bhp at the wheels and the figure provided for the power at the fly was 301bhp.

Re transmission losses, shouldn't 258bhp atw result in a higher figure than 301bhp at the fly ?

Cheers for any thoughts,

Andy

 

think the loss is about 25%.

i had mine done at the begining of march at scoobyclinc and was running
218bhp at the fly and just over 165bhp at the wheels

 

I thought dyno dynamics rolling roads like the one at scoobyclinic were around 21% loss, the dastek is completly different so id say the figures he gave you are right

 

A UK 5 speed tranny loses will be between 23-25%, however, in my experience, most RR's work it out with a pinch of fairy dust..!

 

^^ Agreed! Seems to be fairly random %ages used for transmission losses. My car was RR'd at Surrey Rolling Road who used 19% to calculate power. Bob Rawle then used 22% when working it out after he remapped her

TX.

 

So am I ok to extrapolate 22% transmission losses, resulting in a healthy uber 330bhpish figure for the pub ?

 

But why bother? People would only laugh at you for being such a pillock - i mean really who cares? RR figures are meaningless for the most part.

 

Ouch ! I was only kidding mate !

(I couldn't do that anyway since my mates read Scoobynet too ).

 

IS the Dastek a hub dyno?

 

Eh? What makes you say that fella?

TX.

 

They are only a rough guide, there are so many variables to take into account when looking at transmission losses its almost pointless comparing cars through RR printouts.

Look at tyre pressures, temperatures, maintenance of rolling road, the number of driven wheels, suspension geometry, type of rubber, air temperature etc etc etc, type of drivetrain. The list is endless.... handy for tuning but to determine absolute power not that much use.

300bhp on one road can equal 250 on another. So which do you believe. Apart from the high figure (obvious really).

 

^^^^^

wise words mate..

 

Well ... if a standard car tests at circa 300bhp (Jap import) then the RR must be there or thereabouts. Tested again at same RR after some mods must give a good indication of new power!

TX.

 

How can you tell what power your car has then?

TX.

 

In reality cars tested on the same dyno on the same day can be compared.

Cars tested on different types of dyno, well, as above, it's a rough guide.

 

2 arguments here...

Losses are often talked of as a percentage, yet when an RR corrects to flywheel (unless using pre-inputted data) they measure the actual loss, so do runs at two different boost levels, but the RR loss would be the same amount so different percentages...

In reality neither is right, measured losses are only correct at the load the transmission is under at the time (next to none!), and you will need at add about 5% for the extra losses incurred under load due to the extra bearing load due to the side forces etc.

Simon