170 HP 2006 Miata : fact or fallacy ?

MAJ:
> mistake again. If I thought for one minute the Miata had any
> input from Ford, I wouldn't own one.

44XS11E >

"But they do and you do...."

The original design of the Miata predated the involvement of Ford I
think. I doubt there is a single part designed by or manufactured by
Ford in the NA or NB Miata.

Leon van Dommelen >

Martin Jackson > 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."

While I joined SAE thinking I would have a career in cars, I ended up
working on aircraft gas turbine performance. My job was to determine the
cause of deficiencies in test method or engine build. I wouldn't buy the
spec either as a hobbiest. That's what the company/school library is for.

"Note that these standards are *voluntary*."

That's true until you specify the spec. While individuals will
circumvent the rules, the lawyers and associated government reps will
attempt to conform.

The following comments reflect your distrust of the manufacturers and
the SAE which no one can debate. I am not now a committee member, but
they are generally motivated by the reduced cost and competitive
advantage specs provide. Without specs, your paranoia would be
warranted. That's not to say that no one fudges.

"It appears then that there was a need felt for "fair, accurate ratings"
to formulate this standard, don't you think?"

Yes, but this relates to honest errors as much as evil dooers

"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".

The NY Times article I read indicated the Corvette (for example) was
able to increase its ratings. Again, it is interpretation of the spec
that causes much trouble.

I can assure you from personal experience that the SAE is a non profit
organization. In fact, it is probably loosing money. The 'general
public' isn't the SAE's customer except as it benefits from reflecting
regulatory requirements.

> My look at power from a lot of engine specs suggests that the values are
> pretty good.

O.K., 'pretty good' should read 'pretty comparable'

> Losses from a train of gears and connections, inertias
> and tires really add up.

On the road

"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 (3%), Torsen differential with equal wheel speeds L/R
(2%, sliding), rolling resistance of two tires on a dyno or four tires
on the street with two under load.

Every bearing, universal joint or bevel gear contributes. If the car
restraint increases the tire loading, that loss is increased.

Inertia is counted as production, *not* loss, on the road,

This confuses me. Overcoming inertia while accelerating is a loss

"...and is small on normal dynos such as the ones my car was on."

It is true I was thinking EPA schedule testing or on road loss.

> 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?"

From reducing the test data from about 10,000 engines. Honest
variability and poor equipment calibration & maintenance are two
causes.

Was there a manufacturer challenged in court and retesting with a
witness produced the same numbers? What manufacturer(s)? What car(s)?

It doesn't get to court in my arena; the customer can get an engine
from someone else. Wasn't the production Miata rating challenged ?

> (low atm. pressure)

Don't dynos use a correction factor for that?

The data reduction would correct if measured and calculated properly.

"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........."

I could spend hours in an engineering library looking up these
numbers. Not needed for my current interests. If you do testing to
maximize your performance, the important thing (ignoring bragging
rights) is the change due to some modification. 'all else being equal'
__________________________________________________ ____________________

Martin Jackson > wrote:

> The 'general
> public' isn't the SAE's customer except as it benefits from reflecting
> regulatory requirements.

I agree.

>> My look at power from a lot of engine specs suggests that the values are
>> pretty good.
>
> O.K., 'pretty good' should read 'pretty comparable'

That is hard to dispute.

>"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 (3%), Torsen differential with equal wheel speeds L/R
>(2%, sliding), rolling resistance of two tires on a dyno or four tires
>on the street with two under load.
>
> Every bearing, universal joint or bevel gear contributes. If the car
> restraint increases the tire loading, that loss is increased.

2 hp (the equivalent of a space heater in heat coming out) in the
universal joint, another two hp in each wheel bearing. Add less than a
hp for the entire gearbox and another for the differential and invent some
more tiny space-heater bearings and you are at 30 hp in a jiffy.

I was wondering where all this heat was coming from, now I know: it
are the wheel bearings and u-joints.

>"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........."
>
> I could spend hours in an engineering library looking up these
> numbers.

And not find them.

> Not needed for my current interests.

Well, thanks anyway.

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