Why do motorcar engines stop at V12? why isn’t there a V 16 or V20?
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Buggati makes a W16 basically two VR8 engines on a common crank. VR 8 is basically two inline 4s with a very narrow angle between them. A v16 would probably be double the length. Lots of times it’s packaging. Look at a VW CC for example you can get a 2.0 inline 4 turbo or in the same space you could get a vr6 naturally aspirated.
Also development cost, servicing cost. Yes most above 8 cylinder engines for cars are in very expensive vehicles so service cost may be less of an issue but it’s a bad look for service times to be super long. Buggati has a 20000$ oil change because you basically have to disassemble the back half of the car.
Ever heard of the bugatti veyron / chiron ? They have a V16. It is named W16 because each bank on the V does not have 8 cylinders in a line, but 2 lines of 4.
There arent bigger car engines for the same reason cars dont have 6 or 8 wheels: they dont need it.
More reciprocating mass and friction losses. Heavier. More complex. Longer or wider, meaning bigger car.
V12 has great balance so tends to be the top of the cylinder count.
Apart from efficiencies, there is the issue of size. How big would the front end of the car need to be to fit a V12 or V16 engine. Even if you use pistons the size of tomato paste cans, you are adding a lot of space, and weight. The question then becomes is the additional size worth it.
Soon to be automotive engineer here. Here’s the basic gist of it.
1. Size. The current standard engine is between 1L and 2L and has 3-4 cylinders. A V16 or a V20 is gigantic. The biggest running engine is a W16, 2 V8 engines “fused together”. This was the compromise exactly: due to space. Cars would’ve been massive.
2. Pollution. Making a smaller engine more efficient is a lot easier than a bigger one. The bigger one has more moving parts, more variables, a lot more friction, bigger weight, needs more air, uses more fuel, a gigantic hassle.
We’re in 2022 and global warming is a towering threat upon humanity. We’re barely meeting new pollution criteria for V8s, having to resort to technologies like cylinder deactivation and the like. A V16 or V20 is impossible to do currently without major struggle.
3. Design. Such a long and potentially powerful engine won’t stand a chance when it’s this long. A small 3.0L V8 is 50cm long (around 1.5 feet). A 6.0L V16 would then be around 100cm (3 feet). Can you imagine how much that damn thing will wobble and flex and just refuse to cooperate? By making it cooperate we would have to downtune it massively, so the net gain is, simply put, a net loss.
4. Power. Technology got insanely far. If we can get over 800 hp out of a V8, why would you want to bother creating a more powerful V16? Just make that thing even more powerful and don’t bother with the complicated V16.
Obviously, the V20 is an even worse offender in all the categories.
Consequently, smaller engines were the most useful step forward.
Static need(power), increased technology(production of power).
The need for Power has stayed the same and the technology to produce the output needed has improved.
We no longer need 12 cylinders to produce the power needed we can do it with 4. The power required has an upper limit to usefulness in this particular application.
When I was in high school my shop teacher was in a casual discussion about v12 engines, some of which had four valves per cylinder, and when someone mentioned a possible v16 version he said, “can you imagine doing a valve job on that and having to grind sixty-four valves!?”
Interesting point, Mr. B. Sometimes too much is just too much.
A V12 is physically a very big engine. Packaging it in a modern car is difficult. A V16, with 33% more cylinders, would be even bigger, heavier and more cumbersome. This is why it has rarely been tried in cars, and even when it was it was in specific niche categories like racing and luxury cars. Cadillac and Marmon built V16 luxury road cars in the 1930s, while Cizeta built a V16 supercar in the 80s. Auto Union and BRM built V16 F1 cars, AU before WWII and BRM in the 1950s.
Other companies have built other types of 16 cylinder car engines, mainly for racing. Porsche built a flat-16 version of their mighty 917 sports racing car, but decided to build a turbo version of their flat-12 car instead as they felt it had more potential. The resulting 917/30 turbo flat-12 Can-Am car was known as the ‘Turbopanzer’ and was for a long time the most powerful circuit racing car ever built. Bugatti also built a car with a U16 layout, which was effectively two separate inline 8 cylinder engines geared together.
In the 1960s, not content to rest on their laurels with the insane 1.5l supercharged V16 they built in the 50s, BRM entered the 3.0l F1 era with a monstrosity called an H16, which was effectively two 1.5l flat-8 engines mounted one on top of the other. It was, unsurprisingly, big, heavy, complex, unreliable and caused mounting problems as it had to sit very high to let the exhausts of the lower bank of cylinders pass underneath it. It somehow won one race before it was replaced with a V12.
I have never heard of a V18 or V20 being designed for car use, as by the time you get to that many cylinders the engine’s crankshaft potentially starts becoming very long and flexible, meaning the engine can develop issues with vibration, fatigue and even harmonics, causing it to rip itself apart from the inside. I am willing to be proved wrong, though, if anyone knows of such an engine.
Size.
I used to work with stationary engines running on biogas, turning it into electricity. They were often V16, V24 and V36.
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