[Diy_efi] RE: Diy_efi digest, Vol 1 #413 - 12 msgs

[Adam Wade]

--- Shannen Durphey <shannen at grolen.com> wrote:

> Using a braking type dyno to tune a car for WOT can
> produce misleading results.

Not in my experience...

> A lightweight car with a high power to weight ratio
> would typically never see the same load and duration
> that can be applied with a brake type dyno.

How do you figure?  All that power goes into
overcoming aerodynamic drag, and either you accelerate
with it, or you reach a steady state where the power
produced is equal to the load from drag.  If you can
add more braking with a brake, the rpms drop.  With an
eddy current brake, anyway, you hold a certain rpm
with a certain throttle position, and map for that
load.  Max load given by the brake should be WOT at
best horsepower; no more.  One can certainly expect
the vehicle to obtain that loading condition at some
point in its life.

> Running up to a specific rpm and holding that rpm
> while fuel and spark are tuned in will tend to heat
> parts more than they would be heated in "normal"
> operation.

I disagree.  Unless you're talking about a
grocery-getter.  And in any case, you will get the
conditions in component heating in the real world that
you would on the dyno (give or take a small margin),
assuming you have adequate cooling in the dyno room;
if you drive the thing in low-load conditions, you'll
get the heating you see with low-load testing.  Same
goes for high-load conditions.

> The consequences can be more fuel/ less spark than
> optimal get dialed into the final tune. 

Again, a number of years of fairly constant
dyno-tuning experience with motorcycles disagrees with
that assessment.  Again, though, the dyno rooms I was
using were either outdoors with very hugh-flow fans
and ducting, or with exceptional exhaust fans indoors.
 Temperatures are constantly checked while tuning, and
are almost exclusively found to be normal operating
temperatures.  Very few real-world tuning changes need
to be made after leaving the dyno (unless we're
talking about a system that switches back and forth
between open-  and closed-loop a lot, where
transitions are perhaps more important than perfectly
optimal open-loop mapping).

> The inertial loads alone provide more than enough
> resistance to provide an acceptable street and
> competition tune for these vehicles.  

I suppose it depends on what you consider
"acceptable".  At the AMA Superbike races, losing
isn't considered acceptable, which is why even teams
sponsored by Dynojet often get their bikes tuned on
eddy-curent dynos trackside.  My experience has been
that any motorcycle tuned by anyone on a Dynojet dyno
can be tuned better on an eddy-current dyno, and I've
yet to see that belief disproven.  I have a hard time
believing that machines making MORE power would fare
much better on an inertial dyno.

> To think that you can get a tune right "to the
> gnat's butt" on _any_ type of dyno is to assume that
> you will be running under the same conditions
> always.

It's to assume that you ride around on a dyno.  That
never happens.  And I believe I've said several times
that a dyno is a tool, not the end-all, nor should
anyone think it is.

However, if you get bad results, or end up needing to
do more work than if you had not used it (or used
something else), then it's time, energy and money
wasted, IMHO.

> A wide band sensor mounted in the tailpipe can be
> used to provide a successful tune, just like reading
> plugs can be used to provide a successful tune.

Well, so far in this thread we've had one person with
experience explain that changing the ignition timing
can change the reading on a WBO2 sensor, without
changing the fueling.  And it's pretty well-known that
plug chops tell you if you have the right heat range
plug for the engine and fueling, and nothing more. 
You CANNOT use plug chops for effective tuning unless
you ALREADY KNOW that you have the optimal heat range
for your engine.  THEN they can tell you something.

> To say that the length of the exhaust makes the
> sensor's readings useless only implies that the
> tuner doesn't know what to do with them.

Er, who said anything to that effect?  IF you're
assigning those ideas to me, you've significantly
misread what I was saying.

> For many, many street cars, WB + inertial dyno +
> competent tuner is very satisfactory.

I said that several times as well.  Will it give best
results out of the available tools?  No.  Will it be
close to perfect coming off the dyno?  No.  Will it
get you a lot closer than spending the same time
driving the car around, trying to rough out a map for
a new system just installed on a vehicle with no base
map?  Yes.

Would I rather spend my money on an eddy current dyno
with a four-gas?  Absolutely.


=====
| 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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