AutoSpeed - Torque Converter Transformation

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...

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.