non-lockup torque converter for AOD transmissions, stalls at 2800
rpm behind a 5.0 engine.
With most other brands of AOD non-lockup converters you must buy
a one-piece 3-4 input shaft to eliminate the lockup function.
However Emerald eliminates the lockup function inside the converter
itself, allowing you to keep the original 3-4 shaft and save some
can make you a torque, in whatever stall speed you require, for
virtually any Ford automatic transmission, including C6, C4, AOD-E,
and Photography by Chirag Asaravala
face it, if you want quarter mile performance straight off the dealers
lot an automatic is not a good option. Automatic transmissions, in stock
form, give up a significant amount of power compared to their manual
counterparts -the hydraulic coupling is less efficient, the gear ratios
aren't as low or as abundant and, to add insult to injury, they weigh
more. So does this mean if you've got an automatic equipped car you're
destined to run several tenths slower than a comparable stick car? Fortunately
the answer is no. A few modifications can get your slushbox running
right along side a four or five speed, with all of the benefits that
an automatic has to offer. In fact when we bought our AOD equipped '88
Mustang, the first mod we had planned was to swap in a T5. But the AOD
grows on you quickly -not having to use your left foot or right hand
in heavy traffic, being able to eat a burger and adjust the radio simultaneously,
never missing a shift...hey automatics definitely have their advantages.
So we decided to hold off on the five speed, and see what we could achieve
with the AOD. The results have been surprising. A set of 3.55 gears
and a TransGo shift kit has put the stock 5.0 car into the 13.90's on
radials. Heck, that is better than many five speed Mustangs. We started
to wonder what a higher stall torque converter would get us. Higher
than stock stall converters are the key to achieving maximum performance
out of an automatic car. Many people make the mistake of modifying the
engine with better induction components without changing the stall converter
to match the power band. This usually leads to disappointment in the
vehicles performance, and eventually the automatic is ditched for a
are two rear covers, also referred to as the impeller. You
can get an idea of the vane angles by the impressions in
connect directly to the input shaft of the transmission.
The outer vanes catch fluid thrown off the impeller. Fluid
is then directed through the inner vanes and then the stator.
also have different vane shapes and angles which affect
as it mounts in the turbine.
turbine placed facing the impeller. Welding on the front
cover would complete the assembly.
uses a billet steel front cover for increased strength.
Torque converters are somewhat of a mystery, and their function can
be difficult to understand. We'll try to make some sense of their function
here without getting into the physics of fluid dynamics.
Simply stated, a torque converter functions to transfer and multiply
engine torque to the transmission. This is accomplished via the precise
movement of hydraulic fluid, under centrifugal force, within the converter.
To understand this concept, think of two fans facing each other. If
one fan is on, and the other is off, the air flow from the running fan
will turn the blades of the other fan. A torque converter works the
same way, but uses fluid rather than air, and several other components
to actually multiply the energy and create a mechanical advantage.
A torque converter
consists of four major components, a rear cover (impeller), a turbine,
a stator, and a front cover. The rear cover is typically the image that
comes to mind when you think of a torque converter -the dimpled side,
that slips into the transmission. The dimples are actually impressions
of the impeller vanes. The front cover is the end which connects to
the flywheel, it is welded to the rear cover to form a leak free housing.
Inside the converter sits the turbine, a vaned element facing opposite
the impeller, like the two fans facing each other. The stator sits in
the center of the turbine and also has vanes with specific pitch angles.
The turbine and the stator are the only components that connect to the
transmission input shaft.
As the engine spins it drives the impeller, which forces fluid out the
impeller vanes and against the vanes of the turbine, causing it to rotate
and drive the transmission input shaft. The stator is the middle element
and is held stationary (hence the name) against fluid flow by a one-way
clutch bearing, and redirects fluid flow from the turbine to boost impeller
action and thus multiply engine torque.
When the fluid flow within the converter approaches maximum fluid flow
(known as Vortex flow) the stator begins to freewheel in the same direction
and same rate as the turbine and impeller. At this point the torque
multiplication stops and the converter essentially becomes a fluid coupling.
What is stall speed?
speed is the point when a converter has reaches it's maximum fluid flow
and torque multiplication has peaked.
Stall speed is determined by the number, shape and angle of the vanes
in the impeller, turbine, and stator. Other factors, such as the physical
size of the unit, clearances between the impeller and turbine, and strength
of the vanes also determine the stall speed. Stock converters have a
multiplication ratio of around 2:1, while a higher stall converter (due
to the changes mentioned above) could be as high as 2.8:1.
The point of selecting a higher stall converter is to find one which
stalls close to the peak power range of the engine. If an engine makes
peak torque between 3000-3500 rpm, a converter which stalls at 3000
would give the car a much quicker acceleration and launch, compared
to the same engine and a stock converter which started the car off at
1800 rpm. Therefore the stall speed of a converter is not only determined
by its design, but also by the power band of the engine and camshaft.
Another way to look at this is to think of a manual transmission and
clutch. At the race track you could rev the car to 3500 rpm and dump
the clutch, and assuming the clutch did not slip the engine and driveline
would couple and the car would launch hard. A torque converter offers
the same advantage, but it is constant and not as hard on the driveline
-how often can you dump the clutch on the street?