velohead66

short and sweet, but just need to clarify......

...if someone is talking about a 400 bhp car, then is that at the flywheel, or at the tyres ?


flame suit now on

bigsinky

in the uk its usually at the flywheel. US figures use at the wheels

velohead66

Thanks Mate.
Now puts some technical threads into context.
In Aussie, it's generally ATW (at the wheels).

chaffe

iTrader: (1)

manufacturers nearly always quote flywheel hp, i think it makes more sence personally, because frictional losses are different in every gear. If someone quotes whp, then what gear are they using? they should really quote "whp in 4th gear" etc

velohead66

I know what you are saying.
I suppose there is that old chesnut of 2wd vs awd cars, and what power loss occurs between flywheel and road wheels. Some think it's a percentage, others think it's absolute.

Although, I wonder what peps think an average classic, say a MY98 JDM with the quoted "280PS" [~276bhp] according to the gentlemans agreement, looses in 4th gear.

chaffe

iTrader: (1)

also cars that use active 4 wheel drive like audi s3, golf r32 and 4motion, volvos and the like, the transmision loss is constantly variable, as these cars are basically front wheel drive until wheelspin occurs. From a personal point of view im more interested in what bhp the engine makes, rather than the whp, rather than quoting whp i think "bhp/ton" is a more desciptive method as vehicle weight is a major contributor to acceleration, also should we now start quoting coefficient of friction through the air? and that changes with speed too, where does it stop?

velohead66

I suppose scooby's don't have the most 'efficient coefficient of drag' , unlike some lower down cars like a Skyline or 300ZX.


I've alway's liked the bhp/tonne measure, though


Yes indeed, where does it stop.
One last question, as I do not know the answer, but someone will....
My MY98 gets 300bhp ATW (225kW) in 4th Gear.
So what would be an estimate of bhp at the flywheel , please ?
I have no idea whatsoever.

I accept that the answer will be 'approximate'.

jura11

iTrader: (7)

Hi matey your 225KW is 301BHP(Flywheel)
Converting kW to bhp
1 bhp is equal to 0.746 kW
1 kW is equal to 1.34 bhp.

Here is online calculator
http://www.americanmachinist.com/Cal...rseToKilo.aspx

Hope this help


Jura

velohead66

It's 225 kW ATW (that's 301 bhp ATW, let's say 300 bhp ATW, nice round figure for sake of 1 bhp).
So I wonder what 'that' is at the flywheel ???

I've got no idea haw many bhp (or kW) get lost thru the drivetrain.

chaffe

iTrader: (1)

was this not calculated on the coast down on the dyno when it was rolling roaded? that is the only real way to check transmision loss.

velohead66

Not sure about this, not sure what the operators can/cant do or what they do/dont do.
Maybe I need to ask about this next time it goes on the rollers.