begins on the Tech, Tests & Installs page HERE)
torque converter is merely a reaction to one of two things;
a force applied (being the engine) or a resistance (being
the car). The torque converter harnesses the engine's
power so it would make sense that the more power you make,
the tighter the converter needs to be and the less power,
the looser. The same principle applies to the vehicle.
If it is heavier, it presents more of a resistance and
therefore requires a tighter converter; lighter equals
less load and hence, a looser converter and so on. Installing
a larger camshaft and a better flowing set of cylinder
heads can actually require a looser converter even though
you've made more power. What you have done is moved the
power further up in the RPM range. Now you need to get
the car to leave in that range and therefore, need a looser
converter. If you were to add stroke to the engine and
increase cubic inch instead, you'd be making more torque
as well and the same converter could need to be tightened
“Outlaw” Lock Up converters utilize a clutch
pack that locks the converter up solid, resulting in 0%
slip. It can be activated with fluid when used in ATI’s
SG4 or compressed air when used in a Bruno or Lenco drive.
this picture we can see the individual parts that make up
a torque converter. To the right is the “pump”
side of the converter. The angle of these fins help determine
the stall of the converter. Left shows the turbine sitting
inside the outer cover. This is what your input shaft goes
into. Bottom left is a stator. The number of blades and
the angle of the blades is the biggest determining factor
in the stall. This piece locates on the stator tube of the
front pump in your transmission.
as simple as changing gear ratio or tire height will change
where the converter flashes. This leads us to another point;
where does a converter flash? Or the most common question
"What's my stall?" While you can pull the chip
in the two step and matt the gas for a second to see where
it flashes too, this isnt the best way or the most accurate.
This process shows where the converter goes in regard to
the force applied, but it does not take into account the
resistance. The best way to check the stall speed or "flash"
is to watch the tach when you leave the starting line. The
next best way is to perform the following test in a safe
environment: put the transmission in high gear (assuming
you have a manual valve body) and let the vehicle begin
to roll. Keep it about 5 mph or so and whack the throttle.
Watch the tach and you will see it jump up and hold at a
certain RPM before accelerating. That number is the actual
flash or 'stall'. You have now put the converter in a realistic
environment with both the force applied and the resistance.
a converter to a combination is a critical key to making
your vehicle perform to its full potential. For instance,
ATI recently had a customer with a car that ran very well.
The customer took the engine, transmission & converter
and put it into a similar car in all respects except weight.
It was the same body, same tire & gear and he put the
same engine & transmission with the converter in the
new car. However, the new car weighed 400 lbs heavier. What
he discovered was that in the new car the converter whaich
had worked so well previously now slipped substantially.
By creating more resistance, he pushed through the converter
showing that he required a tighter converter. We see a similar
situation in nitrous cars. People want one converter to
run both normally aspirated and on a heavy nitrous hit such
as 300-400 horse power or more. While it can be done, it
can't possibly be efficient both ways. It needs to be looser
on motor and tighter on nitrous. They need two different
ATI converter parts are made in house. Here you can see
the inside of a stator being machined to accept the patented
sprag assembly. In some cases, sprags are replaced with
a solid hub making them “spragless” but the
stator stays the same.
Eliminator cars require looser converters to get the weight
moving as quickly as possible. It is very common to see
low ETs with slower MPH out of these cars.
with this information we can deduce that every combination
requires its own converter. If you make a change in the
combination, you will most likely benefit from a change
in the converter as well. Again, converter efficiency is
key. Something too efficient without enough power to drive
it will slow a car down and something not efficient enough
simply keeps the power from finding the pavement. The percentage
of slip that is considered "acceptable" really
depends on your power level and vehicle weight. Starting
out with a horsepower level in the 500 range would require
a converter to have a certain amount of slippage to work
properly. As you begin to make more power, you can begin
to bring that percentage down. Its like having enough power
to pull a certain gear ratio. Look at Stock Eliminator cars,
they typically have a higher rate of slippage in the converter
and a lot of gear due to the fact that they make very little
power comparably but look at how they 60ft. Now look at
a Pro Mod making a substantial amount of power ... it has
a lot less gear and a larger tire all the while the converter
has a very limited rate of slip if any at all. Most Pro
Mods with ATI Super Glides these days are using lock up
converters providing zero percent slip.
choosing the right torque converter may not be as easy as
one may think, however it’s certainly something worth
taking the time to learn about and definitely something
that needs to be right in order to be at the front of the
pack. That's why ATI requires a detailed information sheet
when building a custom TreeMaster Converter for each and
Sales & Tech
ATI Performance Products
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or visit www.atiracing.com.