THE TRUTH ABOUT DYNAMOMETER READINGS
AND HIGH STALL TORQUE CONVERTERS
There
is a misconception and a lot of misinformation about
the poor vehicle
performance numbers that are generated by testing a car
with a high stall
torque converter on a dynamometer. Most people that are
not familiar with
how a torque converter operates will automatically think
that the torque
converter is inefficient. This is totally false and the
following facts are
why you should not believe the dynamometer numbers while
using an unlocked
high stall torque converter. All late model dynamometers
have a software
program that commands the loading and speed of the vehicle
over a certain
period of time while making a test pull. The software used
in these
dynamometers is setup to be used with a locked 1:1 connection
between the
engine and the rear wheels, such as using a standard shift
transmission in
3rd gear or when an automatic transmission has the torque
converter clutch
locked. When an unlocked high stall torque converter is
used to make the
pull and the dynamometer software has not been changed
to allow for the
fluid coupling differences the dynamometer readings will
all be bogus. For
instance, the low rpm torque readings will be high due
to the torque
multiplication of the torque converter being run in partial
stall. Likewise,
the high rpm torque readings will be low due to the long
period of time the
dynamometer takes to allow the torque converter to transition
from partial
torque multiplication to a hydraulic locked condition.
The only cure for
this phenomenon is to rewrite the dynamometer software
to prevent this from
happening. Torque converters with a low STR or low stall
are not as
adversely affected by this phenomenon. The high rpm transition
problems
never occur when the vehicle is being driven or raced normally.
Therefore,
worrying about what the dynamometer numbers are is a total
waste of time. If
your dynamometer operator refuses to alter the software
to give correct
readings then the only things you can do is (1.) lock the
torque converter
clutch and do the testing, (2.) use the readings you get
with an unlocked
torque converter as a baseline and continue to tune the
car like normal
until you get the best numbers remembering these are just
numbers and not
the actual horsepower and torque or (3.) use a dynamometer
shop that gives
you the service you deserve for your hard earned money.
The only really true
test of the performance of a vehicle is to take it to the
track and see what
ET and MPH the car will run.