Do manufacturers quote flywheel or wheel horsepower?

[Krikkit]

Whatnotacos said:

SnailTrail said:

I'm fairly sure they normally quote the power the engine makes.

OT but don't they dyno the engine minus a lot of auxiliary stuff as well to increase the figure?

It would not surprise me, could even be making much less.

I always thought that a DIN horsepower was the best flywheel figure you could look at, as they're standardised to be all ancillaries except alternator/ac etc (i.e. everything that you need to run the engine alone.)

[CraigyMc]

Krikkit said:

Whatnotacos said:

SnailTrail said:

I'm fairly sure they normally quote the power the engine makes.

OT but don't they dyno the engine minus a lot of auxiliary stuff as well to increase the figure?

It would not surprise me, could even be making much less.

I always thought that a DIN horsepower was the best flywheel figure you could look at, as they're standardised to be all ancillaries except alternator/ac etc (i.e. everything that you need to run the engine alone.)

Does a DIN figure also standardise the environment the engine is operating in?
Air pressure/temp/humidity?
How about the coolant and oil temps?
How about the temperature of the engine itself?
Does it standardise the oil grade used in the engine during the test?
Does it standardise the fuel used, and the temperature of the fuel?
Does it standardise whether a DPF regen cycle is in progress, or if EGR is being used?

All of the above can have an effect on performance.
Unless they are all standardised, there's no controlled comparison. I'm probably missing loads of other variables.

[topcat1]

Scuffers said:

Then why ask?

You do realise that are standards for this stuff?

You think they would just use some random rolling road to get their published speces?

Why bother posting this sort of ultra negative stty reply, just don't bother.

We all know that horsepower is not a perfect figure and does not mean everything in real world situations but it makes it really easy for us commoners to make rough comparisons on how powerful cars are compared to each other.

Anyway what is wrong with asking if a quoted figure is at the flywheel or at the wheels? There will be a big difference and it's either one or the other, which I am interested to know too. Pistonheads appeals to me because of the majority of decent people who are alike in being petrol-headed, have common sense and appreciate mechanics etc, so stupid posts don't fit in IMO (but what do I know I have only posted a few dozen times).

[CraigyMc]

topcat1 said:

Anyway what is wrong with asking if a quoted figure is at the flywheel or at the wheels? There will be a big difference and it's either one or the other, which I am interested to know too.

It's at the flywheel, as previously discussed.

topcat1 said:

Pistonheads appeals to me because of the majority of decent people who are alike in being petrol-headed, have common sense and appreciate mechanics etc, so stupid posts don't fit in IMO (but what do I know I have only posted a few dozen times).

Most people on PH don't have the sort of engineering background Scuffers has.
I suppose if you spend all your time doing proper engineering in depth, then very high level questions like that sound like questions about marketing rather than engineering, largely because they are. Peak horsepower figures aren't really useful for much else.

If it was actual useful engineering stuff we'd be talking about graphs of data.

[Scuffers]

topcat1 said:

Scuffers said:

Then why ask?

You do realise that are standards for this stuff?

You think they would just use some random rolling road to get their published speces?

Why bother posting this sort of ultra negative stty reply, just don't bother.

We all know that horsepower is not a perfect figure and does not mean everything in real world situations but it makes it really easy for us commoners to make rough comparisons on how powerful cars are compared to each other.

Anyway what is wrong with asking if a quoted figure is at the flywheel or at the wheels? There will be a big difference and it's either one or the other, which I am interested to know too. Pistonheads appeals to me because of the majority of decent people who are alike in being petrol-headed, have common sense and appreciate mechanics etc, so stupid posts don't fit in IMO (but what do I know I have only posted a few dozen times).

why?

because it's blindingly obvious, yet people ask the same st again and again (much the same as the power vs. torque threads)

IT GET'S BORING!

if you want to compare power outputs, great, just go with the manufacturer's figures, they are all achieved in the same way using the same methodology.

and to the person going on about DIN, that's just the standard for environmental corrections, as opposed to SAE or the like, what you really want is the figures in the same units (eg. PS or BHP etc) and the same correction (DIN/SAE/etc) - EU standards mean you will normally get HP in PS DIN corrected.

to witter on about wheel horsepower is both childish and pointless, it does not exist as a std unit of measurement.

Yes there are hub-dyno's, like Rototest/dynapac/etc, and yes they are pretty impressive, can be calibrated, and are a very useful tuning/testing tool, but your still measuring something via a whole load of variables, if you want real numbers for engine power, you bolt it to an engine dyno (preferably one that's been certified/calibrated etc).

the only people who go on about wheel horsepower are the aftermarket, ask yourself why that is.

[topcat1]

What I'm getting at, is for some of us we rolling road our cars, if we do any modifications etc is is really handy to RR it again to get a comparison, tweek things etc so be it as it may that BHP is not scientifically correct, it is bloody handy as a unit of comparison if such a thing exists.

There are a lot of people who are after a hot hatch who will look at bhp figures to see if their new choice is more powerful than the old one etc, people I know well spending £30k+ on engines for rallying are happy to go off bhp figures so for me it's not worth ruling out because it's not quite correct.

As to wheel horsepower, it's a lot more useful than at the fly, as my best man found out recently when his Plymouth was losing nearly 100 horses (or around 30%) through the transmission, compared to my 34 bhp loss. If you just go from engine power and have transmission that saps 90% of it then what is the point?

Edited by topcat1 on Wednesday 28th January 15:01

[Scuffers]

and exactly what's the relevance of any of that to the OP?

[Bennet]

Embarrassingly, I'd always assumed "brake horse power" was so called because it was measured at the brakes. Or something.

[topcat1]

It's not, just like your original post.

[DeuxCentCinq]

Scuffers said:

the only people who go on about wheel horsepower are the aftermarket, ask yourself why that is.

Because that's where it's easiest to measure it?

[topcat1]

Bennet said:

Embarrassingly, I'd always assumed "brake horse power" was so called because it was measured at the brakes. Or something.

I am probably wrong, but I think it is do do with the amount of force it takes to "brake" the load, i.e. more power requires more braking force. I assume in the olden days they used a big brake disc or something similar and put pressure on it to stall the engine, a load cell of some kind would tell you how much force you had to exert to stop the engine (or at least the peak value).

[Scuffers]

DeuxCentCinq said:

Scuffers said:

the only people who go on about wheel horsepower are the aftermarket, ask yourself why that is.

Because that's where it's easiest to measure it?

Measure what though?

Look, as a tuning tool, rolling roads are fine, if you're looking at comparisons as opposed to absolutes, they are also useful for testing installations, ie, the cooling system, fuel systems, etc etc.

topcat1 said:

Bennet said:

Embarrassingly, I'd always assumed "brake horse power" was so called because it was measured at the brakes. Or something.

I am probably wrong, but I think it is do do with the amount of force it takes to "brake" the load, i.e. more power requires more braking force. I assume in the olden days they used a big brake disc or something similar and put pressure on it to stall the engine, a load cell of some kind would tell you how much force you had to exert to stop the engine (or at least the peak value).

almost,

Wiki has a reasonable article on it.

http://en.wikipedia.org/wiki/Horsepower#Brake_hors...

main thing to note is that a dyno measures torque and RPM, power is calculated from these (and then subject to corrections for environmentals).

[SonicShadow]

Scuffers said:

Mave said:

Scuffers said:

Err...

Wheel horsepower as a empirical measure, does not exist.

Why not? Surely you can measure power at a wheel hub in the same way you can measure it at a crank?

At the Hubs is not the same as wheels.

Either way, its still not used for quoted specs by OEM's.

And it's nothing to do with using the highest figure, its quoting the engines output, nothing more, nothing less.

Pistonheads - pedantry matters.

[TooMany2cvs]

DeuxCentCinq said:

Scuffers said:

the only people who go on about wheel horsepower are the aftermarket, ask yourself why that is.

Because that's where it's easiest to measure it?

Quite. Can you imagine how popular club/forum dyno days would be if everybody had to remove the engine from the car and install it in a test cell?

[Mave]

Scuffers said:

why?

because it's blindingly obvious, yet people ask the same st again and again (much the same as the power vs. torque threads)

IT GET'S BORING!

But it's not blindingly obvious. You can research power vs torque and MAY get some appreciation of what's going on if you don't get confused by people saying "torque is how far you go through the wall". But why is it blindingly obvious that manufacturers quote flywheel HP? It doesn't say it in the brochures, it's a less relevant way to understand performance, and if you need to know the DIN standards to understand it, it's not blindingly obvious to the layman. If it's boring to you, why bother responding?

[DeuxCentCinq]

TooMany2cvs said:

DeuxCentCinq said:

Scuffers said:

the only people who go on about wheel horsepower are the aftermarket, ask yourself why that is.

Because that's where it's easiest to measure it?

Quite. Can you imagine how popular club/forum dyno days would be if everybody had to remove the engine from the car and install it in a test cell?