We all know how easy it is to coax more kilowatts
from a Ford Falcon XR6 Turbo. Even the naturally aspirated Ford six responds
well to bolt-on mods. But here’s a way to dramatically improve the performance
of your Ford without increasing power – fitting a high rpm stall converter.
If your Falcon has a BTR four-speed auto
transmission and you’ve got a spare AUD$1200, this is an attractive mod.
The Jim Mock Motorsport High RPM Stall
Converter
Melbourne-based Falcon tuning specialist, Jim Mock Motorsport (JMM), offers a modified version of the factory torque converter that
increases torque converter stall speed from about 2200 – 2400 rpm to a maximum
of 3800 rpm. The appropriate stall speed depends largely on the engine’s torque
characteristics.
So what’s the advantage, you ask?
Well, increased stall speed helps improve
accessibility of performance - a big plus when used on engines having relatively
little bottom-end torque. Simply plant your foot and the stall converter lets
the engine immediately rev to its ‘sweet spot’. Instant acceleration.
According to Brendan Mock of JMM, the modified
factory stall converter offers a couple of significant advantages over an
aftermarket item.
“When you use the factory stall converter you know
it will engage positively and there should be no difference in power to the
wheels. Some of the aftermarket converters I’ve seen tend to have some slip even
when they’re supposed to be engaged.
“The other big advantage is price. For AUD$1200 we
will fit the upgrade converter together with an external trans fluid cooler and
new fluid,” he says.
Brendan suggests an external fluid
cooler is an essential when upgrading the stall converter. That’s because the
extra converter slip in city/urban driving increases overall trans fluid
temperature.
According to Brendan, many BA – BF series Fords
also require an engine management mod to accompany the high stall converter.
“In some BAs there’s a protection strategy that
looks at road speed and revs and, if there’s a lot of slip through the
transmission, it will change parameters. It appears to go into a limp home mode
where power is reduced and it will lock into third gear,” he says.
The solution is an engine management change that
is performed using a flash tuner. JMM offers this at no extra cost.
“We’ve had our modified torque converters running
in cars for nearly two years and we’ve never had a problem or complaint. That’s
one of the big advantages of using a factory part – it’s going to be reliable,”
Brendan says.
The high stall converter is suggested for any
stock or modified XR6 Turbo, mildly modified BA-BF atmo Falcons or older SOHC
Falcons tuned to around 140kW at the wheels. Brendan points out that the high
stall converter is not suited for towing on the open road.
Modified
Torque Converter v Shorter Diff Gears
About
now you might be wondering about the advantages of a high stall converter versus
a shorter diff ratio - both approaches improve the accessibility of mid-high rpm
engine performance.
According
to Brendan, there are three main drawbacks associated with shorter diff gears.
“When
you put a really low ratio set of gears into a car it’ll sit on the open road
going RAAAAAAR. That’s not comfortable. And because the engine is always revving
higher it’s going to use more fuel.
“Then
there’s the price.
“It’s
about AUD$1600 to fit a new diff and if it’s an older model Falcon
[pre BA]
you
could be up for more.
“We
use an electronic unit that recalibrates the input to the speedo. But, in some
models, the problem is that the 180 km/h speed limiter now cuts in at about 140
km/h
[depending on the variation in diff ratio]
. The only answer is a chip that
adds about AUD$700 – so it gets very expensive,” he says.
But
there are downsides to the high stall converter as well...
First
is an inevitable reduction in throttle control. While you previously enjoyed
fine engine control in the low/mid rpm range, a high stall converter will give
you a big rush of grunt – regardless whether you want it or not.
Cars
fitted with excessively high stall converters can also be noisy and irritating
to drive in urban conditions. Engine revs are constantly flaring and a
previously quiet and refined car can be destroyed.
And of
course, a high stall converter also isn’t an option if your car has a manual
‘box...
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On the Road
We had the opportunity to drive a Ford XR6 Turbo
equipped with a JMM modified 3200 rpm stall converter and some mild performance
mods (a CAPA intercooler, upgrade exhaust, bigger injectors and a reflashed
ECU).
And we were bloody impressed.
Punch the throttle in urban conditions and the
4-litre turbo engine is almost instantly on full boost and hurtling you down the
road on the verge of wheelspin. Load it up using the brake and sprint away from
a standard start and it’s all too easy create a c-l-o-u-d of smoke...
The high rpm converter certainly helps the engine
operate in the zone where it performs best and, as a result, it feels more
effortless. On the other hand, the extra converter slip means the engine is
revving harder in many transient conditions and this detracts slightly from
comfort levels. The last thing you’d want is an exhaust that drones – you’d go
insane.
Throttle control is also slightly reduced; ask the
engine for a couple of kilowatts and you tend to get a dozen in return. Clearly,
this is a mod that’s about raw performance rather than finesse.
Interestingly, Brendan says fuel consumption is
not sacrificed with the upgraded converter - if anything, he says it has
improved. There are no back-to-back fuel consumption figures available.
Verdict
At AUD$1200, the JMM modified stall converter is
dearer than a typical high-performance exhaust system that will give a bigger
bang-for-buck improvement. But once you’ve done those easy bolt-ons and you want
to make the most of the power you’ve got, this is a very attractive upgrade.
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