No-lift shifting seems like a simple concept. Instead of lifting off the throttle while shifting a manual transmission, you just keep your right foot planted. But there's more to it than that, especially with turbocharged engines, as detailed in this video from Engineering Explained.
A handful of production cars have offered no-lift shifting features from the factory, ranging from the Chevrolet Cobalt SS to the current Cadillac CT4-V Blackwing.
In the Cadillac, there's a twin-turbocharged 3.6-liter V-6, a type of engine where a no-lift shift can be particularly helpful for maintaining boost. However, if the car isn't set up for it, you also risk damage to the transmission. Keeping your foot on the throttle raises engine speed, putting a lot of extra load on the clutch when its time to re-engage.
One way to maintain boost without allowing the engine and transmission speeds to get out of sync is by retarding the ignition. This allows for increased exhaust pressure to keep the turbo spooled up without spinning the crankshaft faster. A fuel cutoff ensures the engine doesn't rev past its redline, while the turbo's waste gate is kept closed to harness the added pressure being generated.
Cadillac's no-lift shift system also keeps the intake bypass valve closed. This would normally open when off throttle to prevent excess air pressure from building up in the intake and getting pushed back into the turbocharger, a phenomenon known as "turbo surge."
In the CT4-V Blackwing, both the throttle and bypass valves stay open while no-lift shifting, ensuring there's plenty of boost ready to go when the clutch re-engages.
The Cadillac CT5-V Blackwing also has no-lift shifting, but that likely produces less benefit with the larger sedan's supercharged 6.2-liter V-8 because there are no turbos to keep spooled up. But it does mean you can keep your right foot down while running through the gears, which is cool no matter what engine you have.