rwkw conversion

[Jimbo2000]

hi all

found a conversion thingy for kw to HP

but not rwkw to normal kw or HP

just wondering how many rwkw you need to have 400HP?

[franks]

rwkw = rear wheel kilowatts ie. power at the wheels.

its not another measurement of power

to get hp at the wheels convert rwkw to hp using kw to hp conversion calc.

to get hp at the crank, then add about 50kw to the rwkw figure and then convert to hp using kw to hp conversion calc.

[Jimbo2000]

Thanks franks let me rephrase the question forgetting about HP

how do you calculate rwkw-kw, can it be done?

[GraemeWi]

The only answer is to put the engine on an engine dyno, anything else can only be a guess.

There will be figures banded about like a fixed percentage loss from the drivetrain (nup! logic says otherwise) or a quoted loss of something like 17kw. It really depends on the individual car and the condition it is in, eg gearbox, diff, the fluids in those etc.

Of course it's nice to be able to tell the world hey my car makes lots of power at the engine, but it's the power at the wheels that actually counts.

A dyno is really for comparitive testing, for example - do a baseline run and then add more boost, the second run will show some improvement (or loss) over the baseline run. Hey this bleed valve improved the cars output by 15% etc...

Cheers,

G

[rbs13]

i think, dont shoot me if im wrong.. usually there is a 27% drivetrain loss??? just subtract 27 or %% from your crank/flywheel or what ever figure

[Nismodified]

There is too much varience to simply put one figure for drive train loss.

all we really have is estimates

[Xeron]

for the most simple estimate, HP at the rear is aproximitly KW at the flywheel.

[T0nyGTSt]

It's anywhere from 20-30% driveline loss for RWD.

Less for FWD... a LOT more for AWD.

My goal is 250rwkW.

~335 crank kW

~450 crank hp

T.

[GraemeWi]

I'm afraid it's one of my missions in life to rid the world of the fixed drivetrain % loss numbers....

Lets take a stock 1975 LH Holden Torana. A nice simple car.

With a stock 'backfire 4' motor, and stock drivetrain it turns the rear wheels on the dyno to 70 hp. Ok for one moment lets assume the drivetrain is stealing 30% (30hp)... so the engine must be making 100 hp....

Lets up the ante and swap out the backfire 4 for a 308 L34 engine. The Torana with the same drive train, now spins out 250hp at the rear wheels. Is it fair to say that without any changes the same drivetrain is now absorbing 75hp?

Now drop in a Repco F5000 engine, the little Torrie is now pumping 400hp at the rear wheels. Now the drivetrain is absorbing 120 hp??? without any changes?

Fixed loss exponents explain this.... (and if the additional power absorbed is lost through heat, 120 hp works out to be 90 x 1 bar heaters, thats a lot of heat!)

kw and hp measure the same thing, just the same as miles and kilometers measure distance. 225kw at the rear wheels = 300hp at the rear wheels roughly.

'Nuff said.

G