Do manufacturers quote flywheel or wheel horsepower?

[Whatnotacos]

Something i have just thought about

When car manufacturers release the power output of the cars, is in flywheel horsepower or wheel horsepower?

For example my Saab 9-3
175hp factory, Does this mean I make around 150hp to the wheels with 15% drive train loss? Or is it 175 + the 15%?

or lets say...202 crank horse power, so 175Hp at the wheels?

If anyone has any input it would be helpful.

[Scuffers]

Err...

Wheel horsepower as a empirical measure, does not exist.

[SnailTrail]

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?

[Whatnotacos]

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.

[Whatnotacos]

Scuffers said:

Err...

Wheel horsepower as a empirical measure, does not exist.

You know perfectly well what I'm getting at.

[Scuffers]

Whatnotacos said:

Scuffers said:

Err...

Wheel horsepower as a empirical measure, does not exist.

You know perfectly well what I'm getting at.

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?

[Whatnotacos]

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?

I asked because I do not know which power they publish, the power at the crank or the power which would drive the wheels (with drive train loss). I think they would have to be accurate but I'm not sure which they are supposed to publish: Crank or minus drive train loss.

Do you know?

[Scuffers]

So, just how do you propose they get 'accurate' figures from something that's totally uncalibrated, has no standards, etc etc?

What do you think?

[Whatnotacos]

Scuffers said:

So, just how do you propose they get 'accurate' figures from something that's totally uncalibrated, has no standards, etc etc?

What do you think?

I don't expect the figures to be accurate,the engine would have variations in power with different atmospheric conditions
as well as of course loss of efficiency of the years.

Let me phrase it this way, Do they quote the crank/flywheel horsepower in the specs? however accurate they may be.

(Never did I mention accuracy, power output changes with many different factors)

[RobDickinson]

They quote engine power withotu drivetrain.

Dyno's often measure the energy taken by the powertrain in a run down and use that to back calculate the engine power.

[ging84]

it's at the fly wheel

of course it is, manufactures are always going to go towards quoting the bigger numbers

[Whatnotacos]

RobDickinson said:

They quote engine power withotu drivetrain.

Dyno's often measure the energy taken by the powertrain in a run down and use that to back calculate the engine power.

Thank you very much, that's a straight answer!

[Whatnotacos]

ging84 said:

it's at the fly wheel

of course it is, manufactures are always going to go towards quoting the bigger numbers

I suppose that makes sense, why would they say it would make 150bhp when they can say it makes 175.

Thanks very much

[fausTVR]

As said, at the flywheel, but with as much smoke and mirrors as the fuel economy stats. Why not?

[Mave]

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?

[Scuffers]

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.

[TooMany2cvs]

Mave said:

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

Yes, you can. But there are a whole raft of extra variables included, which are then dealt with by fudge-factors.

This article's been floating around t'internet for many years :-
http://homepage.ntlworld.com/johnnya/max-boost/int...

[Mave]

TooMany2cvs said:

Yes, you can. But there are a whole raft of extra variables included, which are then dealt with by fudge-factors.

This article's been floating around t'internet for many years :-
http://homepage.ntlworld.com/johnnya/max-boost/int...

Yes, but that's really talking about the additional errors associated with a "plonk your car on the rollers" set up. I don't see why you can't attach dynos directly to the wheel hubs to get a wheel hub power measurement just as accurate* and controlled as a flywheel measurement.

• with a bit of extra dyno control to keep the wheel speeds the same

[Mave]

Scuffers said:

At the Hubs is not the same as wheels.

It's pretty close. Wheels themselves don't absorb much power. Tyre horsepower is another matter...

[TooMany2cvs]

Mave said:

Yes, but that's really talking about the additional errors associated with a "plonk your car on the rollers" set up. I don't see why you can't attach dynos directly to the wheel hubs to get a wheel hub power measurement just as accurate* and controlled as a flywheel measurement.

• with a bit of extra dyno control to keep the wheel speeds the same

Because you've still got a whole stack of drivetrain in there, adding variables. Sure, using a chassis dyno (they are about) instead of a rolling-road will remove tyre losses from the equation, but that's all.

There's a very strong argument, though, to say that wheel horsepower is all that's actually relevant...