The ‘DSG Burp’ is a cultural phenomenon in South Africa – more so than it should be, really. The excitement that can be drawn from the ‘burp’ of a DSG equipped Golf GTI in unreal, with children screaming in joy, women going weak at the knees, and men losing their minds in pleasure. I’ve seen many a car buyer opt for a DSG equipped Golf GTI over a manual purely for the noise it produces on upshifts; but what causes these burps – why do dual-clutch transmissions burp?
The science behind the noise:
Many petrolheads will remember the episode of Top Gear (Series 16, episode 5) where Jeremy Clarkson made the statement that Audi put a device in the Audi RS5 that inserts a single droplet of fuel into the hot exhaust that then ignites and makes the famous burping noise. Now, while Audi doesn’t actually have a special device doing this, the basic premise that excess fuel in the exhaust manifold igniting causes the noise is correct. So, the DSG/DCT burp is caused by fuel igniting in the exhaust.
But why does it happen? Why isn’t the fuel being burnt in the combustion chamber like it’s supposed to?
How dual-clutch gearboxes cause ‘burps’:
If you’ve read our previous Tech-Talk article on types of transmissions, you’ll know that dual-clutch systems are actually derived automated manual transmissions. You’ll also have read that early examples of automated transmissions were horribly jerky to drive, particularly at full tilt – case in point the BMW M3 CSL with its SMG gearbox.
In a traditional manual transmission, when you shift gears, you lift off the throttle slightly to allow the revs to stabilise and drop slightly whilst engaging the next gear. An automated manual transmission requires the same sort of action, however since drivers don’t have to use the clutch and gear shift themselves, they often kept their right foot planted flat on the throttle – as you do in a car with an automatic transmission. This causes the revs to rise, and when the next gear engaged, there would be a massive jerking sensation as the gearbox was not in sync with the engine speed.
In order to circumvent this, Volkswagen came up with the concept of retarding ignition timing at the crucial moment of the gear change, effectively mimicking the act of lifting off the throttle. However fuelling and valve timing remain unaffected under this programming setup. This results in excess fuel being deposited into the combustion chamber, remaining un-ignited. When the next gear is engaged, ignition of the fuel is resumed via the spark plugs, and the excess fuel in the combustion chamber and exhaust manifold ignites creating that lovely “vroomph” fart/burp that we all know and love.
Volkswagen were the original pioneers of this setup, but since then, the setup has caught on and gained massive popularity for the aural theatre it provides. Manufacturers now rig their dual-clutch setups for prolonged ignition retardation to create all sorts of false bangs and pops on upshifts – case in point Mercedes-Benz and the A45 AMG.
Can only cars with a DCT burp?
Technically, no. Cars equipped with manual transmissions can also burp, however one needs to learn precise timing on when to lift off the throttle in order to achieve the over-fuelling necessary to create the burping phenomenon. Modern dual-clutches have it hard wired into their programming, primarily for smoothness purposes, and can execute a burp almost anytime they are under a heavy throttle load.
There you have it, the reason why your dual-clutch equipped car burps on up shifts. It’s not because of some special mechanism, but rather the transmission timing. So next time a girl swoons at your DSG-created antics, or you find yourself grinning from the aural pleasure, you know why it’s happening and what causes it.