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

Shannen Durphey shannen at grolen.com
Wed Dec 18 05:32:15 GMT 2002



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

> > 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?  
Easy.  Using the dyno, I can apply enough load to keep a 200hp Honda at
1500 rpm indefinitely.  Unless it's hooked to a trailer full of horses,
there's no way that Honda will see the same load for the same amount of
time on the street.  It only passes through that point in a fraction of a
second on its way to "somehwere else." 

> 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.

Are you considering time?  It's the "at some point" that makes the
difference.  As a wild example, consider the dyno load causing the engine
to take 5 minutes to reach 1500 rpm vs the same engine getting to 1500 rpm
in a second on the street.  There's going to be a lot more heat produced
during the 5 minute pull than the one  second run.  The longer the engine's
exposed to heat, the more the heads will heat up, the cooling system will
heat up, radiator, engine comp't...  After 5 minutes of dyno run time you
can bet engine conditions aren't the same as the "real world."

A different example:  Set the brake to maintain a specific rpm.  We can
accelerate to close to that rpm with minimal effort, and we can stab the
throttle right as we get to that rpm.  The perfect dyno will hold exactly
enough brake to maintain that rpm.  So now you're running at the desired
rpm.  You have to take readings, maybe change settings.  How long does this
take?  10 seconds?  5? 2?  How does this time compare to the time the enge
spends at that rpm and load when it's not tied down?  How much more do you
heat the engine?

> 
> > 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),
No, give or take a large margin.

How about a different example. If we can think of a vehicle as a dyno, then
we can consider the difference between a heavy, loaded truck and a
lightweight car with the same engine.  The truck spends more time at WOT
with rpm changing less.  It builds more heat in the chambers, at  the
plugs, in the cooling system.  If we are tuning this truck, then we see
that as heat increases the tendency for detonation increases.  We both know
there are ways to fix this.  We can adjust spark and fuel to prevent the
heating/detonation from occurring.  And when we're done, the calibration we
end up with is safe for the vehicle.

The problem occurs if the engine is taken from the heavily loaded truck and
placed into the lighter car.  There are few clues to tell you the
calibration could be better.  There's certainly little sign that fueling or
spark is wrong.  Depending on when you look, you might catch clues from the
plugs. But fuel and spark are not really "wrong."  It's just that they
could be better.

> assuming you have adequate cooling in the dyno room;

Cooling is a big part of the issue.  Maybe this will help.  Compared to a
bike, you could think of a car as having inadequate cooling on the street,
and usually less in the dyno room.

> > 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.
Consider the mass of the engines you're tuning.  Think of the airflow
around the engine, the size of the cooling system versus the size of the
engine, the materials the engine is made from.  I'm not going to say this
is fact, but I'd bet it's a far cry easier to remove heat from a finned
head, relatively open chassis bike engine than from a car's or truck's
engine.


>  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 

Not trying to be a prick, but how do you know?  What I mean is, are you
looking for signs that something is wrong, or signs that something is
right?  It's awful hard to find a clue that things are performing at their
best.  Even the top dawgs know their stuff is only working better than the
guy at #2.

> 
> > 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".  
Point taken. 

> 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.  

Ok, but racers are paranoid.  Smokey Yunick once said something like "If I
showed up at the track one week with dog turd on my hood, next week
everyone would have dog turd on their hoods."  To be fair, if I wanted to
make changes to my car on Race Day, and I'd found that an eddy current
dyno, or an inertial dyno, or a bag of angry cats tied to the fuel cell
gave me results that I trusted, then that's what I'd use at the track.  The
game is different on race day.



> 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.  
Are you saying that you've back to back tuned between different types of
dynos, or are you comparing stories with other people, or are you judging
by bikes that others have tuned which you're retuning? 

I plead no contest to this example.  I can't prove true or not true.  But
for the general implication that a tune will be better on a specific type
of braking dyno because of the type of dyno, I say there are  exceptions.

> 
> ...time, energy and money wasted, IMHO.
Agreed, 100%


> 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.  

Now you have two people with experience saying it's true.  But it's
important to understand why and when this will happen.  Changing timing
changes the start of the burn and affects the end of the burn.  You can
easily push some of the reaction into the exhaust pipes by playing with
timing.  Since the O2 sensor measures oxygen between the exhaust and the
fresh air, it will "see" an increase in the amount of oxygen in the exhaust
as a change in AFR.  The closer the sensor is to the exhaust ports, the
more oxygen it will see, and the more it will be affected by timing
changes.  At the end of a street car exhaust, all this "outside" combustion
is done.  I've actually heard one guy claim that changing from 100 octane
race fuel to street fuel richened his mixture.  It seemed less of a miracle
after I checked O2 sensor location.


> 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.

I don't agree with that.  If you pick a plug, and run it, and it shows
lean, you can add fuel.  If the car's speed/response/power falls, you can
add timing.  By doing this you will find the optimum fuel and spark for
that plug.  Switch to a colder or hotter plug and try again.  When you're
done, you will have found the optimum fuel/spark for each plug, and the
trend of times/ speeds will point to one or two plugs as optimum.  It does
work, but it's slow.  My point was that it's a tool just like the WB.

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

My apologies.  You were advocating moving the wideband closer to the ports
to reduce delays in sensor readings.  I thought you were saying that the
delay was a "bad thing."

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

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

I did my own comparison years ago between inertial dynos and braking dynos,
and braking won.  I also have issues with the Dynojet user interface, but
that's a different story.  But I think it's important to make the
distinction (and you have) between bench racing dynos and the general
usefuleness of any type of dyno.  Every step forward is a good one, and the
more "the consumer" becomes aware of what it takes to make a good
calibration, the less likely he will be to support vendors that sell junk. 
Getting guys onto a dyno is a big step toward furthering that
understanding.

Shannen

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