Torque converters are sealed
units. Their innards rarely see the light of day, and when they do, they’re
still pretty hard to figure out. The torque converter in an automatic
transmission serves the same purpose as the clutch in a manual transmission.
The engine needs to be connected to the rear wheels so the vehicle will move.
It also needs to be disconnected at some point so the engine can continue to
run when the vehicle is stopped.
A torque converter works like
having two fans facing each other. The first fan is on, and it will blow air
over the blades of the second fan, causing it to spin. But if the second fan is
on hold, the first fan will keep right on spinning. Instead of using air, the torque
converter uses a liquid medium, which cannot be compressed (oil), otherwise
known as transmission fluid. The spinning impeller pushes the oil against the
turbine, causing it to spin. But if the turbine is held still, the impeller can
keep right on spinning. There are two types of stall speed-foot brakes stall
and flash stall. Foot brake stall is the maximum engine rpm achieved from a
complete stop with the transmission in gear, the brakes applied and the engine
at full throttle. The rpm reached just before the vehicle begins to move
forward is the true stall speed of the torque converters.
Before you even open a torque
converter catalog, you need to think about the type of engine you have or are
building. For the street, you need to match low and midrange engine torque to
the converter’s stall speed. For instance, nitrous oxide and supercharges also
affect the torque converter selection. An engine with a power adder produces
more torque than it would if it was normally aspirated. That means a nitrous or
blown engine needs a converter with a lower stall speed range. Otherwise, the
converter will stall too high, causing it to slip and eventually self-destruct
due to the extra heat.
So as you can see, the torque
converter isn’t just a “little black box.” It is a complex device that, if
properly tuned, can have a tremendous impact on your vehicle’s performance,
economy, and durability.
Sunbelt Valve Body Builders
4819 N Cortez Ave Tampa, FL 33614
(813)961-5560
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