Recently on the EngineLabs Facebook page, an infographic was posted showing a “V5” engine configuration, among others. The comment section exploded with commenters claiming there was no such thing as a V5 engine and the graphic incorrectly displayed an inline-five engine.
In fact there have been more than one V5 engines produced throughout history, with the most commercially successful version the Volkswagen VR5. Produced in the late-1990s through the mid-2000s, it was unique in that it had a 15-degree cylinder angle, but a single cylinder head. “It would more appropriately be called the VR5 engine, as it’s a VR6 engine that has chopped off one of the cylinders,” explains Jason Fenske of Engineering Explained.
Luckily, Fenske has created a whole video explaining the odd-duck VR5 (AGZ 2.3-liter, two-valve) engine which makes our life easier. He goes in depth explaining the design, reasoning, as well as the physics behind an inherently imbalanced engine.
As Fenske points out, the VR5 existed as an “in-between” engine option for cars which Volkswagen wanted more power than a four cylinder engine, but less power than a VR6 engine offered. With the physical size of the VR5, it would fit an engine bay designed to fit either option.
The Technical Details
“The firing order is 1-2-4-5-3, so it operates in a clockwise circle,” Fenske points out. “That firing order is the same as an inline-five-cylinder. [The VR5] engine is actually a lot like an inline-five-cylinder that got smashed together and the cylinders kind of bunched up. Dynamically, how everything works is very similar to an inline-five-cylinder.”
While functioning much like an inline-five engine the VR5 definitely was its own animal. Starting with the 15-degree cylinder angle incorporated into the block. “One of the interesting things is the cylinders are at a 15-degree angle. To get the 15-degree cylinders not to contact each other, they had to push them outboard and offset them,” Fenske says.
“By doing that, the centerline of the cylinder is not in-line with the centerline of the crankshaft anymore. That offset changes the angularity of the rod’s motion creating a unique set of motions, different for the upstroke and downstroke.”
Moving up top, is where the debate between the VR5 being an “V5” or a “staggered inline-five” exist, as it only has a single cylinder head, intake manfold, and exhaust manifold. “It has a single valvetrain up top, which is a cool thing VW has done with the VR engines,” Fenske says.
“Another thing that is interesting about this engine is how they have oriented the cylinders. They have flipped the chamber orientation around on the opposite side, so that the intake and exhaust valves are opposite on each side. You have a single intake manifold and a single exhaust manifold on the other side of the engine. The flipping of the port allows runners to be paired up for cylinders inside of the cylinder head, which simplifies the cylinder head design a little.”
A Balancing Act
Having a different number of cylinders on each side of the engine may seem like an issue, but in practice, it wasn’t a large obstacle at all. “From a balancing perspective, you have two cylinders on the left, and three on the right. By having a different number of cylinders you have a different [rotating] mass on either side,” Fenske explains.
“Ultimately most of that can be balanced out with the crankshaft counterweights. But there are likely to be some unique vibrations to deal with within the engine.” However, more than odd vibrations, the only real oddity experienced by VR5 engines was the unique exhaust note.
While time has neither exalted nor condemned the VR5 engine design, it certainly has created an interesting bit of trivia that it appears not many are familiar with. “It was a ‘happy medium’ engine, which may have made sense at the time,” Fenske concludes. “It had more power that an inline-four-cylinder, but was more compact than an inline-five- cylinder. It’s interesting to look back and see something as strange as this actually made it into production.”