Re: 170 HP 2006 Miata : fact or fallacy ?

Martin Jackson <mjackson@xxxxxxxxx> wrote:

> By tradition and currently for comparisons on a fair basis, Shaft
> power from the engine is measured on an engine dyno to SAE J1349.

You seem to know something about those things. In particular, thanks for
the reference. That makes it easy to find:
http://www.sae.org/certifiedpower/details.htm
Unfortunately, I am not going to spend $50 for a standard. If you
have a summary somewhere available for free, I would like to see it.

Note that these standards are *voluntary*. Unless the manufacturer
specifically cites the standard SAE J1349 or SAE J1995 with their
horsepower number, they can essentially do what they want, as long
as it does not stand out too obviously from what other, equally
marketing driven, manufacturers do.

You might note that while SAE is an independent agency, they make
money selling workshops, standards (see above), research, and
books to the manufacturers. (I get an incredible stream of such
advertisements from them in the mail, having bought some technical
books from them. They apparently think I am a professional in the
automotive area.) I do not see SAE being too hard on manufacturers.

The above web page says:

"The new voluntary SAE power and torque certification procedure ensures fair,
accurate ratings for horsepower and torque as it uses third-party
certification," It appears then that there was a need felt for "fair,
accurate ratings" to formulate this standard, don't you think?

"J1349 was updated last year to eliminate some ambiguities that allowed
engine makers to cite power and torque ratings higher than the engine's
actual capabilities." I do not need to comment on this, except that
somehow it does not say "lower".

"SAE will create a database and offer it to industry in different packages
and at different price points." Yes, they will, at a high price, which
means the entire process is largely untransparent to the general public.
Do you think the insurance industry is going to worry about whether
car buyers really get the hp they are entitled to? Or that they might
think, "the less the better." Do you really think the EPA or the federal
government would be any different? Major car magazines depend on the
goodwill of the companies for "scopes" on new models, and for timely test
cars, as well as for the advertising revenue that keeps them in business.
I am glancing at Motor Trend here and it is chock full of color advertisements,
many over two pages, by car manufacturers.

> My
> look at power from a lot of engine specs suggests that the values are
> pretty good. Losses from a train of gears and connections, inertias
> and tires really add up.

You must have numbers that I do not have, because I come nowhere close.
Please give us specific numbers from gearbox losses in 1:1 gearing,
Torsen differential with equal wheel speeds L/R, rolling resistance of two
tires on a dyno or four tires on the street with two under load. Inertia is
counted as production, *not* loss, on the road, and is small on normal dynos
such as the ones my car was on.

> Now, the manufacturer can get a witness certified rating, but I can
> testify that this won't really improve the numbers.

That is interesting. How can you testify to that? Was there a manufacturer
challenged in court and retesting with a witness produced the same numbers?
What manufacturer(s)? What car(s)?

> Just variations
> in build tolerances cause more than 3 % error in production.

Excuse me, but is that not a big loophole for the manufacturers right
there? The witness monitors the testing, but presumably not the
selection of the engine and first break-in?

> What organization would 'require' a change.

I never said there was one. See my notes on insurance industry,
federal government, and car press above.

> The government does
> require the power consumption of the car at constant speed for their
> dyno loading. And, if you run air conditioning,

Actually, I believe that everyone who measures hp on either a dyno
or on the street turns off the A/C? I sure hope so, I would not
like to get the numbers of someone stupid enough not to. :)

> are at high altitude
> (low atm. pressure)

Don't dynos use a correction factor for that?

> or it's a hot day,

And for that? Also, I know that my car was measured at essentially
sea level and normal temperatures.

> you could loose 10 %

Let me see now: If I run my air conditioning during the dyno test
and do it at a high temperature and high altitude, I can lose
*as much as 10%"? And this is to explain that if I *do not* do
any of this idiocy, I lose 25%?

> not to
> mention locking differentials,

How many people measure hp going through a curve, or on a dyno with a
big and a small rear wheel?

> low tire pressure,

Flat tires are especially helpful in increasing losses.

> winter tires

Lots of people using dynos on Miatas with winter tires mounted, I am
sure. However, I am in Florida.

> and
> having the top down.

Somehow, I do not think dyno data are that much affected by having the
top down, and some people use the top-down drag coefficient in road
testing, which is only 10% or so more than the normal drag coefficient
anyway.

>Car & Driver and Road & Track ready to stand tall for this for a change???
>
> They really don't want to be part of that argument. They just tell it
> like it appears to them as you do.

Sure. See my observations on the automotive press above.

>I guess it would cut down on advertisements $$$ for automatics. :(
>
> Not a logical or relevant point. Automatics are a feature some folks
> need.

Let's give a *full* quote of what I said, not? Here it is:

] But I agree that it would be nice if manufacturers were required to
] report actual, rear wheel horsepower instead of some technical,
] immeasurable number. Car & Driver and Road & Track ready to
] stand tall for this for a change???
]
] I guess it would cut down on advertisements $$$ for automatics. :(

I would say that it is both logical and relevant that to cite a lower
hp number for automatics because of their higher losses would be
undesirable marketing.

>As Craig says yes. The engine hp cited is supposedly measured with
>some load, ("brake",) at the engine crankshaft. Unless you plan to
>take your engine out and use it to power your home generator, what
>you really care about is what horsepower comes out at your rear
>wheels, which is measured with a dyno.
>
> A 'dyno' is used for the engine power measurement;

Heywood, page 45: "Engine torque is normally measured with a
dynamometer. ... The value of engine power measured as described
above is called *brake power* P_b. The power is the usable power
delivered by the engine to the load -- in this case, a 'brake'."

> a drive wheel
> dyno or a vehicle dyno measures drive wheel power.

Commonly referred to simply as "dyno".

> Again, the engine produces the power and there are several ways to
> burn it up before getting to the road.
>
>(Dyno's might be optimistic.)
>
> Aside from cheating, yes, there are many ways the dyno can lie
> including bearing problems and ignorance of proper techniques.

And there are many reasons dyno operators may want to be optimistic,
including customers wondering where all the power they thought
they had went. ;)

> While you make every effort to get the correct absolute power,
> more important is consistent readings test to test.
>
>Where does the other 25% go? There you have me. The few numbers I
>have seen for gearbox loses (especially in high gear) and differential
>are nowhere near to explaining the loss of a quarter of the power.
>
> Differential,

As above: please tell us how much it is.

> Air Temperature,

As noted, this is corrected for in case it makes a significant
difference.

> bearings,

If you mean gearbox losses and clutch bearings, please give us
the losses at a 1:1 (4th gear) gearing.

> fluid coupling,

Viscous limited slip differential? Please give the losses at equal
L/R wheel speed. And why is this not included in differential?

> tires,

What is your number for the rolling resistance? (including the
velocity dependent part if that makes the difference)

> alignment,

Is not alignment included in the cited number of rolling resistance?
Or are you saying the wheel bearings eat up 25% of the engine hp?
Does that not make their oil quite thin?

> air cond., headlights,

Somehow, I turned them off on the dyno. Strange, not?

> electric fuel pump, computers.......

Regardless of the fact that it seems very unlikely to me that these
two would make any big dent in losses of the order of 30 hp, in addition
they perfectly illustrate my point that the standards allow the
manufacturers to get away with murder. The fuel pump and computer
are *necessary for the engine to run as advertised." Allowing
the manufacturers to omit their power requirements allows them
to, say, put a cheap, grossly power wasting fuel pump on the car
without having to change their cited horsepower number. The
manufacturer gets to cite the original number, the customer loses.
The same for alternator losses as they affect power required for
operation of needed engine components.

>I read somewhere (here or elsewhere) a vague explanation referencing
>"accessories". Some heavy accessories.
>
> Many years ago, the test standard tightened up the 'accessories'
> issue, but the load on the generator and air cond. pump are variable
> 2
> as a function of battery 'soc', cabin temp. I don't begrudge anyone
> else their automatic trans. or air conditioning, but they are not
> performance options.
>
>Horsepower is a big selling point, not?
>
> As testified earlier, power spec is a contractual value

As the SAE web page I cited above clearly points out, unless it
specifically mentions an SAE J standard, it is an *undefined*
contractual value. That is not much of a solid contract, is it?

> and the
> manufacturer really doesn't want to be caught too far out.

I do not know your definition of "too far out."

For an independent tester to test, he/she would have to collect a
number of identical cars, take their engines out, put them on a test
stand and measure hp. Then, if the number turns out to be noticeably
lower than cited by the manufacturer, the manufacturer can still
argue (probably correctly) that their procedures are consistent with
what other manufacturers do, so that they were simply following
"established practice."

>From your knowledge of the SAE standards involved, it appears that
you may know something about those matters. If so, please give us
typical numbers for the major losses in a typical sea-level, normal
temperature dyno setting by component, and show us how they add up to
something like 25%. I am sure I am not the only one here who would
be very interested to see that.

Leon
--
Leon van Dommelen :) Bozo, the White 96 Sebring Miata .)
rammm@xxxxxxxxxxxx http://www.dommelen.net/miata
EXIT THE INTERSTATES (Jamie Jensen)
.