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How is a Dynapack different?
The first and most obvious difference is the elimination of the tire to roller interface on a conventional roller
dyno. The Dynapack eliminates this variable by using a hub adapter that provides a direct coupling to our
Power Absorption Units. There can be no tire slip, no rolling resistance, and no chance of the vehicle
coming off of the dyno at high speeds. Notice that we call this a variable. Sometimes it may be a problem
area, other times it may not. Tire temperature, pressure, traction, etc, are all variables that can change - not
only from run to run, but during the run as well. Throw an unknown variable like this into the equation and
your data has now become subject to a potentially high margin of error. It is obviously better if these
variables could be eliminated - which is exactly what we have done. There are other associated problems
with the roller method as well. Take tie-down straps for example. Most roller dynos use ratcheting tie-down
straps to attempt to hold the vehicle in position while being tested. If the straps are cinched down tightly, the
tire has become loaded even further, in an unpredictable manner. While this may be good for enhancing
traction, it changes the rolling resistance of the tire - skewing the data further. Since these tie-down straps
aren’t perfect, the vehicle squirms around on the rollers - dramatically changing the tire drag during the run.
If the vehicle is tested in two different sessions, the straps can’t be set exactly the same way twice in a row.
Again, the data will be inconsistent. We have heard of cases where the ratcheting tie-down straps were
loosened by two clicks and the measured power increased by ten horsepower. What if the straps stretch -
either from run to run, or during the run itself? Wouldn’t it be great if all of these problems could disappear?
With a Dynapack, they were never there in the first place.
Another major difference is the effect of inertia. Street wheels and tires spinning at high RPM have a large
amount of inertia. A large steel drum spinning at the same ground speed has much more inertia. What you
end up with is a giant, heavy flywheel attached to your engine. The inertia is such, that just trying to
accelerate the mass of the roller is a substantial load for the engine. That is the principle that some roller
dynos (or “inertia dynos” as they are also called) operate on. Accelerate a known mass to a measured speed
over a given time and it can be calculated to equal a certain amount of power. There is nothing wrong with
this theory, but like many theories, its application in the real world can be troublesome. How do you think
your measurements will be effected by being subjected to this large heavy flywheel phenomenon? Will small
fluctuations be noticeable? In a word, no. The flywheel effect tends to take small rapid variations
and smooth them right out - as energy that should be going into the dyno is
being wasted trying to accelerate a large lump of steel. This is great if you want your power curve to look like a smooth pretty line, but it
doesn’t give you much insight into what is really occurring. What if you eliminated the flywheel
effect? While nothing that has a spinning mass has “no” inertia, when compared the total mass of the wheels, tires,
rollers, and other associated hardware of a roller dyno, the inertia of a Dynapack is practically zero. This
allows us to precisely measure and display tiny rapid pulses and oddities that you may not have seen before.
Now you have a window into areas that no roller dyno will allow you to see. Another benefit of having
virtually zero inertia is the ability to change the rate of acceleration at will. In many situations, you may
want to accelerate the vehicle at a different rate to simulate a specific condition. With a few simple
keystrokes, we allow you to make the vehicle accelerate very quickly, slowly, or
anywhere in between. Because of our lack of inertia and total control of the engine speed, we give you choices that none of our
competitors can even dream of - and as you know, choices are good!
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