How Do You Calculate Rwkw From Kw From Hp?

[335]

Hello

How do you calculate rwkw from kw and kw from hp? I have checked online but cant find it.

[TiTAN]

you stick the car/engine on a dyno. different cars, different drive lines, etc. you cant get an accurate answer making large assumptions about what losses are involved.

[icydude]

1 horsepower = 0.745699872 kilowatts

google is a great converter

http://www.google.ca/search?hl=en&q=30...wer+to+kilowatt

[tridentt150v]

An R34 GTT was quoted from factory at 206rwkw, a standard one on the dyno usually got around the 160 mark but it varies according to tyres, different diffs, gearboxes [manual vs tiptronic], even the oil and bearings used.

You can 'safely' say that you will lose at least 30rwkw as a baseline for a skyline. Then it depends on how much power your car makes as to the overall loss.

As a hypothetical example = A 600kw car will be more efficient but still lose more in total than a 100kw car because the harder you work something the higher your friction component. So it might lose 60rwkw but still make 540 and the 100kw car might lose 20rwkw and make 80, as a percentage of total power the 600kw car is then more efficient, 90% vs 80%. It loses more because it is revving harder, and working more thus increasing losses overall to friction.

But it all gets way too hard to actually calculate a result with any certainty, too many variables - so as TiTan said the dyno is the best solution.

[hypergear]

KW = RWKW * 1.15 (Generally)

KW = HP / 1.34

[Galois]

An R34 GTT was quoted from factory at 206rwkw, a standard one on the dyno usually got around the 160 mark but it varies according to tyres, different diffs, gearboxes [manual vs tiptronic], even the oil and bearings used.

You can 'safely' say that you will lose at least 30rwkw as a baseline for a skyline. Then it depends on how much power your car makes as to the overall loss.

As a hypothetical example = A 600kw car will be more efficient but still lose more in total than a 100kw car because the harder you work something the higher your friction component. So it might lose 60rwkw but still make 540 and the 100kw car might lose 20rwkw and make 80, as a percentage of total power the 600kw car is then more efficient, 90% vs 80%. It loses more because it is revving harder, and working more thus increasing losses overall to friction.

But it all gets way too hard to actually calculate a result with any certainty, too many variables - so as TiTan said the dyno is the best solution.

Why will it be more efficient?

I would have thought the more power you're producing at the fly, the more you're going to lose through the transmission and diff, in terms of efficiency as a percentage?

I was always told you lose 25% between flywheel and the rubber, but that said hypergear's done a lot of this stuff. Isn't there a way of measuring the power at the fly by determining the friction/resistance/losses through the box and diff? I swear I read about James May explaining it once...

Edited September 15, 2010 by Galois

[KiwiRS4T]

The losses are not a percentage but a number e.g. 25kw for auto 25kw for awd etc. People who think they are making say 30% more at the fly than they are getting at the wheels are most likely being wildly optomistic at higher power levels. In any case the only really useful figure is the one you are making at the wheels v the last figure you were making at the wheels on the same dyno.

[Galois]

Wouldn't the losses change depending on the power put through?

[simpletool]

It'd be some kind of multi-variable equation.

Easiest guess is a percentage say 20% more at the treads.

A better model is a flat number of say 25rwkw plus a percentage of ~10%

The best model would be some multi-variable non-linear equation.

[DVS JEZ]

i dont think he means rwkw to engine hp,

i think he just means RWKW to RWHP

[GTRsean]

An R34 GTT was quoted from factory at 206rwkw, a standard one on the dyno usually got around the 160 mark but it varies according to tyres, different diffs, gearboxes [manual vs tiptronic], even the oil and bearings used.

You can 'safely' say that you will lose at least 30rwkw as a baseline for a skyline. Then it depends on how much power your car makes as to the overall loss.

As a hypothetical example = A 600kw car will be more efficient but still lose more in total than a 100kw car because the harder you work something the higher your friction component. So it might lose 60rwkw but still make 540 and the 100kw car might lose 20rwkw and make 80, as a percentage of total power the 600kw car is then more efficient, 90% vs 80%. It loses more because it is revving harder, and working more thus increasing losses overall to friction.

But it all gets way too hard to actually calculate a result with any certainty, too many variables - so as TiTan said the dyno is the best solution.

Whoa there! factory outputs are always at the flywheel, no as quoted in bold.

Eg a 32GTR is quoted as 206KW (more like 220KW), and stockers put out on average 170RWKW.

[joe blo]

hp to kw = hp / 1.34

kw to hp = kw x 1.34

[ARTZ]

driveline loss in any rwd car on average is usually around 20-25% isnt it?

For eg..500hp engine puts about 300kw(400hp) at the wheels..

works out to 20%

Edited September 15, 2010 by Arthur T3

[R31Nismoid]

It's not 20% - this argument has been had time and time again on these pages.

It seems to be around a "fixed" ~60rwkw amount from all discussions.

It's certainly not 20%. Think about it, 800hp motor is losing 160hp (120kw)? Nope.

If you fix it @ 60kw... GTR's around 220-230kw factory (even though its quoted @ 206, we all know its not).

And most stock GTR's make around 165-180rwkw on a dyno so it certainly fits quite nicely.

Until it's actually tested, which to date no body has, then it's impossible to say overall anyway.

That said - I will investigate with Nizpro & Racepace the feasibility of doing this testing in the next couple of months for everyone along with some other general forum speculation stuff i wanna cover

[tridentt150v]

Whoa there! factory outputs are always at the flywheel, no as quoted in bold.

Eg a 32GTR is quoted as 206KW (more like 220KW), and stockers put out on average 170RWKW.

yeah, good call, my mistake, I meant flywheel kw and if you read it as that the sentence makes sense.