[Diy_efi] Dyno. cooling

[Bernd Felsche]

On Tue, Dec 17, 2002 at 06:22:35PM -0800, Adam Wade wrote:
> --- Bernd Felsche <bernie at innovative.iinet.net.au>
> wrote:

> > You're not considering the car as a whole... an
> > engine's output power is determined by ambient
> > conditions.  Unrepresentative airflow through the
> > engine compartment probably means that components
> > aren't operating at representative temperatures.

> What parts are you concerned about?  We've already
> agreed that a dyno will never be exactly the same as
> real-world operating conditions...  What parts do you
> feel would be operating outside of normal parameters
> given extra airflow?  Considering that the air moving

Air intake for one; temperature sensors for coolant, oil sump,
exhaust manifold temperature and hence O2 sensor... just a few to
start.

"Extra" airflow is nothing like road values unless the supply of
cooling air is covering more than the entire front of the vehicle.

> through the engine compartment couldn't possibly cool
> the components to, say, winter ambient temperatures,
> there's no way you could end up with below normal
> operating temperatures on any component I could think
> of, unless you were designing a Venus rover or
> something.

It's not a question of under-cooling per se. It's about achieving
relative temperatures inside the engine compartment with thermal
flows like those on the road.

> > Somebody else already mentioned that drawing air
> > from underneath the car would be a closer
> > approximation to the real road.
> 
> The ultimate question is, "Does it make a meaningful
> difference?"  I'm not understanding how it could be,
> when speaking of underhood temps.

It depends on the operating points of the engine management system
and how it reacts to changes. It also depends greatly on the supply
of cooling air.

One can conceive of situations where an improvement on a dyno.
doesn't result in an improvement on the road, simply because of the
differences in airflow and hence heat transfer in the engine
compartment. It wouldn't be the first time that laboratory results
couldn't be achieved outside of controlled conditions.

> > In essence what they need is the
> > vehicle/prototype/model moving relative to the
> > ground with the air "attached" to the ground; but
> > they're only moving air relative to the ground and
> > the vehicle.
> 
> Unless it's a "rolling road" wind tunnel.  And even
> that is not PERFECT, simply very, very close.

Who's got one of those?

> > I know that's somewhat esoteric; but keep it in mind
> > when you think about how representative of road
> > conditions the dynamometer really is...
> 
> *grins*  Yes, I keep saying that...

-- 
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