89-99 AWD DSM:
The factory rated the AWD transmission for roughly
250ft.lbs of torque.
This is where
there won’t be a failure of gear teeth pretty much
regardless of how many cycles the parts is subjected to,
assuming that transmissions is in good working condition.
Commonly referred to as the fatigue limit, this
torque rating is
determined by the overall design of the transmission,
gears, shafts, shaft spacing, structural integrity of
the transmission case, size & capacity of bearings, the choice of steel being used to
manufacture the gears,
tooth count, helix &
pressure angles, the manufacture's ability to hold
tolerance on the parts and to what AGMA or DIN that they
cared to produce in the first place
and so on and so on and then ultimately by doing
destructive load testing, both static and dynamic. We have
had several burn offs done to know what choice of steel
Mitsubishi has used in their drive-train products and have
built load cells to conduct destructive testing to
determine the amount torque at which plastic deformation
occurs. We have measured shaft flex and how much axial
deflection the transmission case has in relation to how
many ft.lbs of torque in each gear, paid for FEA's and
have defined the S/N curve. Are the other shops doing
their homework or are they merely claiming some HP
numbers?
Our torque ratings are conservative
and the above text is merely the tip of the iceberg of
what should be done when calculating realistic probability
of survival when it comes to answering the infamous “how
much torque is it rated for” question. Simply put, if
the transmission parts are the OEM ones that you can buy
directly from Mitsubishi, the fatigue limit is roughly
250ft.lbs of torque. Yes you can put more torque into the
transmission but the overall life expectancy of the
transmission will be shortened accordingly.
The most torque that can realistically be put into the
transmission without gear failure is 375ft.lbs. of torque.
For the daily driver who street races and occasionally
goes to the drag strip I would look for a clutch that
holds around 450ft.lbs of torque.
Sure you
can put over 600ft.lbs of torque through the transmission
but don't expect it to last forever regardless of who
builds it. It should
be noted that a customer has successfully put 645ft.lbs of
torque through our transmission for quite some time,
2 seasons of drag racing, but
it is expected that fatigue cycle failure will eventually happen because the
factory parts were never designed to handle this kind of
power for very long.
We have done destructive load cell testing on the DSM
transmission. Listed below are the average peak torque
numbers at which failure occurred immediately during a
static load test of a new AWD transmission. While
the
numbers may appear to be impressive, understand that
failure was immediate and that the dynamic numbers would
be substantially lower.
-
1st gear =
1125ft.lbs
-
2nd gear =
1240ft.lbs
-
3rd gear =
1300ft.lbs*
-
4th gear =
NA*
-
5th gear =
NA*
* Input
shaft splines began to yield at approximately 1300ft.lbs
To put things into perspective, a new off the shelf 4th gear &
intermediate shaft from Mitsubishi has an
approximate service life of less than 1 hour or 10,000
cycles when 450ft.lbs of
continuous torque is going into the transmission.
We recommend using a clutch that holds around 10-15% more
torque than your engine can produce but no more than half
of the dynamic burst torque of the transmission or you
will be substantially reducing the service life of the
transmission.
