The idea of increasing the engine’s compression ratio for the sake of obtaining more performance is not really new. The high-comp heads were actually among the first hop-up parts that became available for the Ford’s Model A four-banger and the famous flathead V-8 engines. However, won’t it be fun if you were able to enhance the squish factor of the piston without having to swap hardware? In today’s featured video of Engineering Explained, Jason Fenske talks about the new tech from the OEMs that will transform this possibility into a reality.
The variable compression ratio is an idea that automakers are trying to optimize both efficiency and power by making alterations to how air mixture and fuel is being squeezed into the power stroke of the engine. Higher compression generally delivers more fuel efficiency and power. However, when it comes to the modern turbocharged engines, there is a limit to how much squish can take place before knocking kicks in. By being able to control the compression ratio, more squeeze at lower engine speeds can take place (when a better mpg is required), and pressure can be reduced at higher rpm thus enabling the engine to deliver horsepower safely.
The concept is amazingly cool; however, it has proven to be quite difficult. As of now, Nissan/Infiniti is the sole manufacturer that is offering variable compression in a product (the Altima and the QX50). However, GM has plans of entering the market with a unique design of its own. Jason Fenske of Engineering Explained, as always, does an excellent job of breaking down how the new system operates. He highlights the changes to the crankshaft and connecting rod design for accommodating the on-the-fly adjustments.
While electric vehicle technologies are moving forward at a surprisingly fast pace, the breakthroughs in the internal combustion industry including variable compression ratios, Koenigsegg’s camshaft-less Freevalve magic, the Mazda’s Skyactiv-X compression ignition gasoline, and others are proof that the industry still has a lot to offer.
You can learn more about GM’s patented variable compression engine in the video below!