Infiniti’s Variable Compression Engine (VC Turbo) is Fascinating
There’s more to the Infiniti VC Turbo engine than a fancy crankshaft.
Infiniti used the unveiling of their new 2019 QX50 premium mid-size SUV to showcase some truly incredible engineering. Dubbed “VC Turbo,” the new engine that will power the QX50 is the next step in the evolution of the internal combustion engine. I hope you’re sitting down, because this tech will floor it.
The “VC” in VC Turbo stands for “variable compression.” Yes, Infiniti is bringing out a regular, production engine that can have variable compression on the fly. That is amazing. Watch the short video above to see how it works, and I will fill in the gaps.
I cornered down Christopher Day, Senior Manager of Powertrain Performance with Infiniti, and bombarded him with questions about the VC Turbo engine. Day was amused that someone in attendance had more in-depth technical questions about the engine, so he didn’t hold back in his responses.
Above are overview shots of the VC Turbo engine, what do you see?
Double-click the images for full-size resolution. These general shots are useful for getting a feel for the arrangement of the engine, and everything attached to it. For example, note the oil junction block and filter that are bottom-center. The QX50 uses a transverse engine arrangement, so the intake manifold is in front, and the turbo and exhaust manifold are out back. That last shot looks through the “window” on this display motor, and showcases the VC crankshaft.
The way it works is ingenious. The crankshaft is offset from the combustion chambers. Attached to the crank is a lever arm that rotates 180 degrees. From there, the rods are effectively split into two pieces. However, about 4″ up, the rods attach to a variable roller mechanism. This roller works to keep the rods aligned, regardless of the compression ratio that the lever arm dictates.
The result is an engine that can switch infinitely in a range of compression ratios from 8:1 to 14:1 based on the position of that lever arm in it’s 180 degree of range. Under high load, pulling the compression back means the boost can be cranked up without fear of detonation. This provides strong performance. On the flip side, under low load, like cruising down the freeway, the compression can ramp up to 14:1 and increase efficiency and improve fuel economy. It’s a bit more complex than that, but that’s the basic principle.
Above is the turbo setup on the variable compression engine.
The VC Turbo engine appears to use an integrated manifold. This is where the exhaust manifold is integrated into the head cylinder, and able to be cooled by water jackets. Note that there is no visible manifold leaving the back of the engine, instead, all you see is where the turbo is bolted onto the head. In theory, this reduces Exhaust Gas Temperature (EGT) values, improving turbo longevity and response.
The turbocharger itself is pretty conventional compared to other modern turbo engines. The turbo is pretty small, likely offering sharp low-rpm boost at the expense of top-end power. There’s a fat solenoid on there to control the wastegate. There is a large, single catalyst immediately after the turbo, which is more efficient than a downstream catalytic converter. Max boost is relative to the fueling, ignition timing and compression ratio on hand, but I was told that seeing 20 PSI of boost under hard use wouldn’t be uncommon.
Looking beyond the integrated manifold, the head features 4-valves per cylinder, and uses both port-fuel injection and direct-fuel injection. If the fuel management is setup correctly, this is the best of both worlds. Direct injection offers increased efficiency, and port fuel injection will keep those intake valves nice and clean, as well as helping “fill in” certain areas where the supplementary fueling would be beneficial for smoother engine operation.
So, did I miss anything specific you wanted to know about Infiniti’s VC Turbo engine? Drop a comment, because ut’s very likely I may have asked Infiniti’s engineer during our little Q&A session. Looking forward to seeing how this engine performs in the future.
Want to know more about the 2019 QX50 SUV in which the VC Turbo engine is debuting in? Click the link here for more details!
