[Diy_efi] Dyno. cooling

[Adam Wade]

--- Bernd Felsche <bernie at innovative.iinet.net.au>
wrote:

>> What parts are you concerned about?

> Air intake for one;

The temperature of the air entering the air intake
won't change appreciably at higher speeds, assuming
you are using a dry-bulb sensor (which you should be).

> temperature sensors for coolant,

You're not suggesting that the sensor will read
differently based on increased under-hood airspeed?

> oil sump,

Changing airspeed won't change the speed at which heat
is removed, once the air is moving at least as fast as
the heat transfer rate of the material in question. 
If the pan can't shed heat any faster than the air can
absorb it, then the extra airflow won't take as much
heat per unit volume moving past.

> exhaust manifold temperature and hence O2 sensor...

Unless you are using the exhaust O2 sensor for tuning
(which I never have, and in fact most of the vehicles
I tune don't even include), that's not really an
issue.  In any case, if it were a significant issue,
then a warmed-up car would receive different values
from the O2 sensor in cold weather vs. hot weather,
far in excess of the difference based on differences
in airspeed with same-temperature air (not to mention
needing to control EGT to get reliable, repeatable
readings from an O2 sensor).  I'd think that would
make it useless in the real world.

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

HUH?

> 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.

Since we're not trying to compare engine efficiency,
or reliabliity of components, with those of vehicles
actually on the road, I can't see where it makes a lot
of difference.  I'm not designing an intake system, or
figuring out what temperature a coil pack must resist.
 I'm tuning a vehicle to make best power, given a
warmed-up engine and an IAT of X.  As long as my
engine is warmed up, my sensors are operating
properly, there are no overheating conditions, and the
IAT is recorded, that's all that matters from a tuning
aspect.

>> 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.

I don't see how.  None of the sensors used by the EFI
system should be afftected by airflow at all, as long
as minimum airflow requirements for cooling are met.

> 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.

I certainly can't, unless there is a problem with heat
build-up in places where it gives misleading readings
when on the road.  That's a design flaw, and finding
and fixing it quickly is important.  It can lead to
very unpredictable and changable real-world results,
and presumably that runs counter to our goals.

>> Unless it's a "rolling road" wind tunnel.  And
>> even that is not PERFECT, simply very, very close.

> Who's got one of those?

There are many around the world.  They are used all
the time by F1 teams, car manufacturers, and the like.

A better question might be, "Who can afford to
dyno-test in a wind tunnel of ANY sort, and would
there be any benefit to doing so?"

=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=/   |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

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