Something is wrong here!!!

[blacksax1]

Just got my car back from a one pull dyno and I am shocked at the readout!!! I'm getting ready for a Frank Sidewinder cam and my installer wanted a recent dyno pull so we can check before and after the cam. So I go to a local dyno, mustang, and my numbers are the same as when the car was stock. I'm so frustrated right now. I've had 4 pulls done on my car, all mustang except one dynojet. These are my readouts and mods at the time:

mustang 281hp 310tq K&N CAI, 180 therm
same mustang as above 332hp 343tq K&N, 180, Superchip, JBA system
dynojet 314hp 366tq same mods but with diablo 93 CAI
today diff mustang 281hp 317tq same mods

can someone explain what the deal is? I know that all machines read different, but this one just told me my car is stock......something is not right.:

[WrenchJeff]

Jeremy, take all of this into account.
There is much deliberation around the industry about dyno accuracy.
Just how accurate are the dyno power readings? Why does the
same car get different results on different days? Why does the same
car get different results on dynos from the same manufacturer and
from different manufacturers?

There can be significant differences in the results produced by
the same vehicle when run on different brand dynos and even on the
same brand of dyno.

But some people say that the accuracy of a dyno is not as important
as its ability to reflect the outcome when modifications are made to
a vehicle, and its repeatability. Others say a dyno is only useful as a
tuning tool and does not need to be relied upon to be accurate. Is it
any wonder people get confused. Read on to get an understanding
of the reasons behind the variations in results.

Once upon a time, there were really only 3 key reasons why a vehicle
could show a different power reading on the same Dyno at different
periods in time, they are:

1. The Dyno was not correctly calibrated;
2. The Atmospheric (Weather) Conditions had changed;
3. The Vehicle had a problem that affected its Power Output.

Early chassis dynos were only able to apply load, and subsequent
models were extended to measure some basic outputs like torque,
power and speed. The dyno operator had little influence over the
dyno and had to accept the results that the dyno produced.
Now, would it not follow that if the vehicle was unchanged and
weather conditions were constant, that one vehicle could be
expected to produce at least similar results on several of the same
brand of dyno, or all dynos for that matter?

Is incorrect calibration likely to be a factor? Perhaps, but with
modern dyno hardware, a dyno is not likely to lose calibration
through normal use. Dynos that are available these days have
mostly evolved into state-of-the-art diagnostic tools and keep pace
with the high-tech advances in motor vehicle technology. The better
quality dynos can now generate vehicle specific information and a
level of accuracy that was not conceivable even a few years ago.
Faster computers and the flexibility of the Microsoft Windows
operating system have given dyno programmers a far more powerful
tool than they have ever had before.

So what other factors are involved? We would surely all agree that
any dyno manufacturer worth their salt is interested in producing
accurate and honest results from their dyno. An intrinsic part of
producing accurate, honest and consistent results from a dyno
requires that the dyno dictates the power produced by a vehicle
without undue influence from the dyno operator. Let's look at how
results can be influenced.

THE DYNO OPERATOR:
The evolved dyno operator of today has much greater influence over
the results produced on a dyno than ever before, and the dyno
operator has become another reason why a vehicle can show
different power readings on the same dyno at different periods of time.
Is it possible that at least some operators would mislead a
customer about the extra power produced by an aftermarket add-on
or a performance tune if they were able to do that? In a market place
where more power seems to be better, would it be in a dyno
operator's interest to satisfy a vehicle owner's desire for high power
figures?

Many dyno manufacturers have ensured that the "operator factor" is
eliminated as far as possible, meaning that they lock the operator out
of areas of the dyno controller where results can be "influenced" and
follow a policy where all relevant dyno run factors are displayed on
run files and printouts so that any attempt that has been made to
manipulate the results can be easily identified.

But not all dyno manufacturers have taken that approach. At least
one brand of dyno has built in an easily accessible "correction factor"
that the dyno operator can use to increase or decrease the results
produced, and so, for example, in the hands of an unscrupulous
operator, the "correction factor" could be used to mislead a customer
about extra performance when no performance benefit was actually
achieved. It could also be used to convince a vehicle owner that a
vehicle generates far more power than it is capable of.

VEHICLE INERTIA FACTORING:
Another example of why sometimes people get curious dyno results
from different dyno brands is because one dyno manufacturer may
attempt to factor in Vehicle Inertia while another may not. Vehicle
inertia is best explained as this. If you are accelerating a car, then
part of the torque produced is consumed to accelerate all of the
rotating components of the car, ie Wheel/Tires, Driveshafts, Gears
etc. This is not Driveline Loss, Driveline Loss is the friction generated
from gears, bearings, universal joints and Tire to Roller contact.

There is nothing wrong with trying to account for vehicle inertia,
provided it is used correctly. The problem with applying vehicle
inertia is that not every car is the same. For example, if you were to
change from 17" Rims to 19" Rims on a car, you have effectively
changed the vehicle inertia, because with inertia the further the mass
is from the center of a rotating object, the more inertia there is.

So on a dyno that uses vehicle inertia correction, an operator may
specify an inertia value for a vehicle, say for example a Commodore.
But the available Tire/Rim Combinations from early to late model
Commodores can vary from 14" to 19" Rims. One model might also
have steel rims while another has nice light alloy rims. It is easy to
dismiss this an unimportant, however do not underestimate the
difference in tire/wheel combinations as the Tire/Wheel is
responsible for around 80% of the Vehicle's Drive Train Inertia
because these items have a much larger radius than any other
component in the drive train.

A difference of 8KW's can be seen on a Subaru WRX by just changing
from one tire/wheel combination to another. The chance of over or
under applying Vehicle Inertia is fraught with inaccuracy and can
provide misleading results, and some dyno manufacturers choose to steer
well clear of it. They take the view that at the end of the day, a dyno is
measuring how much power is actually getting to road surface, and the
power that gets to the road surface (Motive Force) will govern just how
quick a car really is.

ATMOSPHERIC CORRECTION
Modern dynos also have the ability to correct power on the basis of
changes to weather conditions. A short explanation is needed here
to fully understand atmospheric correction. Atmospheric correction
is applied to compensate for changes to the combustive properties
of the ambient air (the quantity of oxygen per unit volume) in an
attempt to provide a level playing field between dyno runs.

Atmospheric Correction Standards are defined by organizations
such as SAE, ISO, DIN, ECE etc and each uses a slightly different
way of measuring change. Using the widely accepted SAE J607
standard, on an ideal day when the temperature is 15 degrees
Celsius, and there is 0% humidity, and the Barometric Pressure is
1015mbar, zero power correction is applied. Variations in any of
these three atmospheric factors will either cause positive or negative
power correction to be applied. If the temperature changed to say
19 degrees Celsius, the humidity to 34% and the Barometric
Pressure to 989mbar, the conditions are not as ideal and the vehicle
will not make as much power. By applying the SAE J607
atmospheric correction (in this case +3.89%), the power readings are
corrected to what the vehicle could be expected to make on an
"ideal" day.

The amount of power correction applied to a vehicle always needs
to be an accurate reflection of how much power is actually lost by or
gained by the vehicle as a result of unfavorable weather conditions.
The SAE J607 standard specifies a maximum ceiling of 10% power
correction, on the basis that any power correction in excess of 10%
will produce a power figure that cannot necessarily be reproduced
by the vehicle under optimum conditions.

So, a dyno that can accurately correct vehicle power according to
changed weather conditions should produce more consistent and
accurate results from run to run. A dyno that cannot correct vehicle
power according to weather conditions or where weather conditions
have not been regularly updated can produce results that vary
considerably from run to run. A 5ºC inaccuracy in air temperature
can lead to a 0.9% change in power figures. A 3 mBar (normal range
900 to 1050 mBar) inaccuracy in barometric pressure give a 1%
change in power.

[WrenchJeff]

Follow these golden rules to limit the variations in results between
dyno runs and give you a better idea as to whether the results of a
dyno run can be relied upon to be accurate:
• Dyno Printouts should always clearly show which atmospheric
correction standard was used (eg SAE, ISO) AND how much
atmospheric correction has actually been applied to arrive at the
end result.
• Be wary of any dyno that uses uncapped correction, as it can
produce figures that can never be reproduced even under ideal
weather conditions. If the percentage correction that has been
applied is not specified, there is a good chance that uncapped
correction has been applied.
• If the dyno uses the air intake probe temperature to calculate
atmospheric correction, make sure that the probe is not
improperly placed during the dyno run, and check that the
ambient temperature and the air intake temperature on the
printout are not unreasonably different.
• Use a dyno that provides automatic correction from an inbuilt
weather station, or make sure that the atmospheric conditions
have been updated just prior to the dyno run if the dyno cannot
provide automatic atmospheric correction.
• Make sure that the operator uses consistent test parameters
(gear, start speed, end speed, ramp rate) for multiple runs so that
any variations in results are from the vehicle and not the way it is
tested.

[blacksax1]

I know there are variables that could alter a readout. But a loss of 50hp and torque, is that possible Jeff, of do I need to start thinking something is wrong with the car?

[EZCORPION]

Damn long long message Jeff.... :D

[WrenchJeff]

You may need to look at your tune.

[WrenchJeff]

It looks like you lost power when you switched from the Superchips and went to the Predator anyway.

[Rev Scorpion]

Great write-up Jeff.

Where is that button for the rep points again????

[blacksax1]

It looks like you lost power when you switched from the Superchips and went to the Predator anyway.

I think the reason for the drop was mustang to dynojet. I definitely know the car pulls harder with the predator, but i'll put the superchip back on just to experiment.

[Mecha]

always stick with the same company of dyno and same shop and if you can same dyno tech.

try to keep everything as equal as you can.

try to get same outside temp or close etc...

[CentralTexHemi]

I hate dyno numbers the dyno to me is only good for fine tuning so get to the track (a good one) and if you have timeslips before than compare them to what you are running now, if you have no previous "PRE MOD" timeslips compare your new times to someone elses with similar mods. If you could run some video of 0-100 at wot that will simulate close to a 1/4 mile run and post it up and I will take a look at it. I would also like to see some datalogging from your Predator I would like to see ST KR, LT KR, AMB TEMP, BASE SPARK, #1 CYL SPARK, RPM (Not Eninge RPM) and ENG COOLANT TEMP

[blacksax1]

James from Frank Racing took some data logs for me when I was at the track last time. He said everything was normal.

[Founder]

Beans for that reply, My gosh Jeff

[beandip77]

No joke, that was one detailed message.