Power at the wheels or Flywheel?
Power at the wheels or Flywheel?
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19 April 2005, 04:44 PM
#11
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Because all cars come with a bhp quote from the manufacturer. This is a flywheel figure. Theres no point saying 'my sti has got 220 bhp at the wheels' to mr f360 driver who says, ' yeah but mines got 400bhp because ferrari said so!'
Last edited by Gear Head; 19 April 2005 at 04:47 PM.
19 April 2005, 04:49 PM
#12
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Sorry, I was being sarcastic in my comment.
Given two figures (say 350bhp @ wheels or 400bhp flywheel) any magazine is going to make use of a 400bhp car as it simply attracts more attention and makes a bigger statement.
Whether one is more important than the other is somewhat irrelevant when it comes to the majority of magazine articles or pub talk on bbs's.
Needs more information than a single BHP figure to really mean anything.
Afterall, how many times have you heard talk about 1000bhp Skylines and though, what the **** does that really mean?
Given two figures (say 350bhp @ wheels or 400bhp flywheel) any magazine is going to make use of a 400bhp car as it simply attracts more attention and makes a bigger statement.
Whether one is more important than the other is somewhat irrelevant when it comes to the majority of magazine articles or pub talk on bbs's.
Needs more information than a single BHP figure to really mean anything.
Afterall, how many times have you heard talk about 1000bhp Skylines and though, what the **** does that really mean?
19 April 2005, 06:19 PM
#13
There is merrit for both quotes.
The flywheel power is derrived on a RR by measuring the transmission losses
4 x 4 losses are much higher than 2 WD. This can be a function of poor design/manufacture and installation.
If an Sti 6 speeder looses (say) 50 bhp in losses and an AUDI quattro system looses 30 bhp, then the Subaru is the weaker design.
If a 400 bhp Cossie 2WD looses 30 bhp and weighs in at 1.2 Tonne, and a 1.2 tonne Sti @ 400bhp looses 50 then the Cossie wins.
I wish both nunbers were given so we can see the 'quality' of the trans.
Anyway, all the RR numbers are just that, numbers. True performance is measured on a track in controlled conditions. Lap times count, not bhp.
Graham.
The flywheel power is derrived on a RR by measuring the transmission losses
4 x 4 losses are much higher than 2 WD. This can be a function of poor design/manufacture and installation.
If an Sti 6 speeder looses (say) 50 bhp in losses and an AUDI quattro system looses 30 bhp, then the Subaru is the weaker design.
If a 400 bhp Cossie 2WD looses 30 bhp and weighs in at 1.2 Tonne, and a 1.2 tonne Sti @ 400bhp looses 50 then the Cossie wins.
I wish both nunbers were given so we can see the 'quality' of the trans.
Anyway, all the RR numbers are just that, numbers. True performance is measured on a track in controlled conditions. Lap times count, not bhp.
Graham.
19 April 2005, 07:44 PM
#14
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PAW, imho most important but rarely used because most people who care about such things want to use it for bragging purposes.
Std. Impreza turbo has say 170 AWHP (?) doesnt sound very impressive does it?
if you really want to maximise the potential, use power at fly in american HP
Std. Impreza turbo has say 170 AWHP (?) doesnt sound very impressive does it?
if you really want to maximise the potential, use power at fly in american HP
19 April 2005, 07:49 PM
#15
It's a can of worms.
You can quote PAW, but different rollers give different PAW.
If you are going to compare, you need to ensure the gearbox oil is up to temperature, and that the tyres are the same as the car you are comparing with. If you have some supersoft semi slick tyres you will loose more power then some hard as nails "chindu punjitt" tyres at 60psi.
Dyno shootouts in Oz are now carried out with 40 or 50psi in the tyres (cant remember which, 50 I think) and this is written on the dyno sheet.
If you want to compare acceleration potential then wheel power is important, if you want to compare engine efficiency and the effectiveness of the engine systems and mapping, flywheel power is most important.
Paul
You can quote PAW, but different rollers give different PAW.
If you are going to compare, you need to ensure the gearbox oil is up to temperature, and that the tyres are the same as the car you are comparing with. If you have some supersoft semi slick tyres you will loose more power then some hard as nails "chindu punjitt" tyres at 60psi.
Dyno shootouts in Oz are now carried out with 40 or 50psi in the tyres (cant remember which, 50 I think) and this is written on the dyno sheet.
If you want to compare acceleration potential then wheel power is important, if you want to compare engine efficiency and the effectiveness of the engine systems and mapping, flywheel power is most important.
Paul
20 April 2005, 12:50 PM
#20
The engine has to over come all the car's losses before it moves forwards.
Rolling resistence of the tyres, wheel bearings, brake drag etc and the transmission losses.
The driveshafts in perfect alignment take some power too, wheen they are all 'bent' then the power consumd to move them round and against the forces in the joints also consume more power.
The variation in power loss can be hot oil verses cold oil, less power to turn everything when all is hot, but it is the power consumed by turning over all the oil etc that is converted into heat, hence'Warming the trans up' phrase.
Transmission loss on the RR is only a (big) part of the story, but then in the real world there is the air resistance at speed and other things!
This is why i say the real measure is a lap time on a track.
Paul is so right that this is a can of worms, and why Manufacturers quote flywheel (dyno) bhp. It removes all these questions!
Well, nearly. The Euro method (and USA I think) quote bhp of an engine without water pumps ect (which sap that little bit of power again), power steering pumps are power hungry, hence electric power steering!!
I'm exhausted now
Graham
Rolling resistence of the tyres, wheel bearings, brake drag etc and the transmission losses.
The driveshafts in perfect alignment take some power too, wheen they are all 'bent' then the power consumd to move them round and against the forces in the joints also consume more power.
The variation in power loss can be hot oil verses cold oil, less power to turn everything when all is hot, but it is the power consumed by turning over all the oil etc that is converted into heat, hence'Warming the trans up' phrase.
Transmission loss on the RR is only a (big) part of the story, but then in the real world there is the air resistance at speed and other things!
This is why i say the real measure is a lap time on a track.
Paul is so right that this is a can of worms, and why Manufacturers quote flywheel (dyno) bhp. It removes all these questions!
Well, nearly. The Euro method (and USA I think) quote bhp of an engine without water pumps ect (which sap that little bit of power again), power steering pumps are power hungry, hence electric power steering!!
I'm exhausted now
Graham
Last edited by 911; 20 April 2005 at 12:53 PM. Reason: spelling
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