Spoiler Alert: It's not really much different than other engines.
Volkswagen has a new engine debuting with the 2018 Tiguan called the Budack Cycle that operates a little differently than most, and we do mean little. We'll try not to get too deep into engineering speak on this one – we'll leave that for the Engineering Explained video above. Just know that, in the most basic explanation, VW’s new engine has intake valves that close a few milliseconds early. Here's why that tiny change in operation makes a difference.
The basics of an internal combustion engine are as follows: Air comes in, mixes with fuel, gets pressurized by the piston as it comes up, and explodes. That sends the piston down, which creates the power you use to effortlessly merge on the highway, or for gratuitous smoky burnouts. This is called an Atkinson-cycle engine, and it’s been around since pretty much the beginning of cars.
A variation of this process called Miller Cycle keeps the intake valves open a little bit longer than normal, which pushes some of that pressurized charge back into the intake. This lowers the compression ratio, which basically means the piston doesn’t have to work as hard compressing everything before the explosion. As a result, the engine can run a bit more efficiently but it comes at the cost of horsepower. Volkswagen's Budack Cycle – named for one of the automaker’s powertrain engineers – uses this same principle, only it closes the intake valves a bit sooner than normal, allowing less of a pressurized charge into the cylinder. See, we told you it was a little difference.
Why go through all this trouble in the first place? When an engine is running under a low load, such as cruising down the highway, the Budack Cycle can offer better fuel efficiency as previously described. And since normal cruising doesn’t require massive horsepower, the power loss doesn’t matter. For when the power is needed, the engine can change the camshaft profile not unlike the variable valve timing systems found on most modern engines, returning the valves to a normal mode of operation for a bigger boom.
And now, you’re smarter than you were when it comes to engines.