We’ll start off with the obvious question — if an engine is an inline six-cylinder, how can it be a V6 as well? Well, that distinction lies right in the name of Volkswagen’s VR6. The “VR” stands for “V-Reihenmotor” (Reihenmotor being German for “inline engine”) — or simplified to English, “Inline-V engine.”
So, technically, the VR6 is a V6 engine, with a narrow 15-degree bank angle (along with a variant with a 10.6-degree bank angle). The “inline” naming convention (which was probably done as a marketing move to describe the engine’s compact nature) is where a lot of confusion comes in. While there is only a single cylinder head, a single deck surface on the engine block, and the engine is far more compact than a traditional V6 engine of similar displacement, those facts aren’t what define an engine’s configuration.
So, with that out of the way, let’s look at the VR6, why it exists, and how it works.
The VR6 engine design exists for one reason, and one reason alone — packaging. By having a narrow bank angle and offsetting the piston bores from one another, you are able to fit six cylinders in a package that is simultaneously shorter than an inline-six-cylinder and narrower than a traditional V6 engine. A more compact powerplant allows for far more flexibility in the design of the automobile.
As you can imagine, such a shallow bank angle, a single deck-plane, and single cylinder head pose some engineering challenges. In order to maintain the typical 120-degree firing interval between the cylinders, the split-pin design offsets each bank’s crank journal by 22 degrees. Another aspect of the engine design shared with inline engines is obvious when looking at the crankshaft. The crankshaft bears more resemblance to that of an inline-six crankpin arrangement than that of an even-fire (split-pin) V6 crankshaft.
Just like the block, a single-cylinder head for two banks of cylinders creates some unique considerations. Built in both two- and four-valve-per-cylinder designs, the overhead camshaft cylinder head design posed a unique challenge to engineers. In order to have each intake runner be the same length and volume to ensure that each cylinder was making the same power at a given RPM, they had to get creative, while maintaining tight packaging.
The Volkswagen VR6 engine is a unique beast that has come in a variety of displacements and configurations and has not only bent the definitions of what an engine can be, but has spawned some of the most unique engines known to enthusiasts, including the VR5 (A VR6 minus one cylinder) and the W8, W12, and W16 family of engines (two VR4, VR6, and VR8 engines, respectively, joined at a 72-degree bank angle).
The VR and W lineup of VAG engines are an interesting answer to a problem vehicle engineers have been battling since the dawn of time, and have proven themselves as capable powerplants. Volkswagen engineers have taken interesting approaches to deal with the unique challenges presented by the wild design, and it has earned its place in the internal combustion engine history books.