DCT vs torque converter, which is your preferred transmission?

Jason/Jul 24, 2020 04:01 PM

Back in the early 90s, if you wanted to buy a performance car, you’d most probably choose the manual transmission option. The equivalent automatic option was probably heavier, slower-reacting, and had higher fuel consumption.

My own uncle once told me back then, “In a sprint, my manual car would always be faster and more accelerative versus an automatic.” Those words stuck with me.

Fast forward to today, and self-shifting transmissions have gotten so good, no human input could possibly match its speed and efficiency. Two of the most common types of automatic transmissions today are the dual-clutch transmission (DCT) and torque converter (TC).

Which begs the question, which is the better transmission? This has been a debate that has raged on for some time. Let’s take a deeper look at both ‘boxes.

Dual clutch transmission

VW's DQ250 dry-clutch DCT​​​​​​

In my time owning the MK6 Golf GTI, I’ve always marvelled at the way it went about its business. Its 6-speed DCT (or DSG, in VW-lingo) was smooth, fast and returned very decent real-world fuel consumption.

Push it to manual mode, and the shifts become even faster, accompanied by the signature ‘farts’ on upshifts. This all resulted in a very satisfying driving experience, until you get stuck in traffic. Yes, all the things you’ve read about DCTs being jerky in traffic, are true. Therefore, your crawling habits in traffic needs to change when driving a DCT-equipped car.

The most common criticism that is levelled at the DCT, is that it is unreliable. There have been many conflicting stories about ownership experience of DCTs. Personally, in my time owning the Golf GTI, the DCT performed flawlessly.

Still, there has to be a reason why Ford abandoned its DCT endeavour, so much so that none of the cars it sells in Malaysia now comes with a DCT. All I can say from experience is, the Powershift transmission wasn’t a very good representation of DCT transmissions. It was lurchy, ponderous, and jerky.

Curiously though, Proton has gone the opposite direction with the X70, with the DCT replacing the TC transmission. Having tested the DCT-equipped X70 myself, I can attest that it brings a sprightlier driving experience.

Porsche's PDK DCT transmission is so good, you can concentrate of squeezing out that last tenth of laptime

Which brings me to why the DCT transmission is here to stay; speed. From an engineering standpoint, DCTs are just plainly the faster transmission, in a way that no TCs can match.

That’s why, you still see DCTs in high-performance brands like Ferrari, Porsche, and McLaren, because shift speeds are all-important in their quest to extract faster lap times and 0-100 km/h sprints. Because of this, DCTs will be here for the foreseeable future.

Torque converter

ZF's 8HP 8-speed torque converter, the best of its kind in the world

Torque converter automatics have come a long way since its inception. It was commonly referred to as a ‘slushbox’ because in its early days, TCs were not all that fast-shifting, plus it sapped a lot of power from the engine, thus blunting acceleration and response.

Today, torque converters still retain its inherent smoothness, be it in traffic or while cruising. All this while having less power loss, faster shift-times and better response. In fact, you can’t really call modern TCs ‘slushboxes’ anymore, because there’s nothing slushy about these 'boxes now.

Moreover, TCs have excellent low-speed behaviour. Being stuck in traffic is also less of a chore in a TC-equipped car, as the crawling characteristics of the transmission is seamless and smooth, because you can just ease off the brakes to get the car moving, unlike DCT-equipped cars.

In addition, TC transmissions are generally more robust and are less complex mechanically compared to DCTs. This means that longevity-wise, TC failures are very few and far in between. Couple that with the fact that it can take copious amounts of power and torque, and it’s easy to see why the TC gearbox remains popular as ever.

Currently, the best proponent of the TC box is the ZF 8HP 8-speed that BMW uses. If you weren’t told otherwise, you’d never think this is a TC gearbox. It is swift, intuitive, responsive and while it isn’t as sharp as a DCT going through the gears, the difference now is very marginal.

Perodua's 4-speed transmission, robust, reliable and here to stay

As a testament to just how good this ZF 8HP, this very gearbox is deployed in cars such as the F90 BMW M5 and A90 Toyota GR Supra. This just goes to show that a well-engineered, well-tuned TC box’ can be just as good to drive as a DCT, even from a performance standpoint.

Conclusion

Threading the neutral line, I would say that both transmissions has its pros and cons, as outlined. The good thing is that, they both have their place in the automotive world. I would like to think that it was the advent of DCTs that forced manufacturers to up their game and refine the TC transmission.

This means there can only be one winner, the consumers. However, I’ve been greatly impressed with the strides that the TC transmission has made over the years. While the DCTs have gotten a bad reputation (some unwarranted), TCs have quietly and constantly improved, and as such, deserves praise.

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