Why do motorcar engines stop at V12? why isn’t there a V 16 or V20?
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There is, kind of. VW makes a W16 that’s essentially two V8’s slapped together(not really, but we will pretend)
There were v16 engines back in the 30s. Back then, engines were so inefficient that some luxury cars had them to make any appreciable power. But they were huge. Nowadays, engines can make much more power in a smaller package, so engine bays don’t have to be huge to accommodate the engines of that size.
The Bugatti Veyron has a W16. And I think there are a few others with similar engines.
But generally, as you increase the number of cylinders in an engine, the power increases but the efficiency decreases. This is typically why you see a lot of 4 and 6 cylinder cars since they have the best split between power and efficiancy.
There used to be, back when engines weren’t very efficient at making power.
Back in the 1930’s, it took 7.4L of displacement and 16 cylinders to make 165 horsepower (Cadillac series 452). For comparison, my wife’s FIESTA makes 196 horsepower out of a tiny (turbo) 1.6L 4-cylinder and my 3.5L supercharged v6 puts out 324hp at the wheels.
As technology improved, we were able to make more power with less fuel. A 7.4L modern engine could easily make over 1000hp.
There are W16 engines on sale today in some very high end sports cars. That actually sort of proves the reason why we got rid of engines like this though. They’re just too big. The Bugatti Chiron is basically all engine and radiators, with two seats as an afterthought. And that’s with the clever packaging of a W16 which is “smaller” than an equivalent V16.
A V16 engine is *enormous*. You have 8 inline cylinders that each need a certain amount of real estate, and then you have a second bank of the same that needs to be offset to the side.
For comparison, there were cars that used to use straight 8s, and they were also enormous. These are cars like the Duesenberg Model J, which had a hood about 15 miles long.
[https://en.wikipedia.org/wiki/Duesenberg_Model_J](https://en.wikipedia.org/wiki/Duesenberg_Model_J)
So, the reason we don’t use these engines anymore is basically size and weight. Displacement used to be the only practical way to make power, but it also means your car has to be big and heavy.
You get better efficiency and even performance out of a smaller engine, provided you can make the same (or enough) power. That’s why F1 cars now have tiny 1.6L V6s that make ~700hp. *And* they can go around corners because they’re not carrying 1,000 lbs of engine.
the more moving parts the less efficient and more maintenance.
as a teen my dream car was the Lamborgini Espada, it had a v12 (ferrari stopped using them I think they started using the inventory) with six carbs (a real PITA to tune) and it turned out some 320 HP. You can buy family sedans with that much today.
When the oil embargo crashed the economy, and smog concerns required engines to be more efficient the engineers actually figured out how to do it. IIRC the Honda Civic engine was the first to have a pre combustion chamber, a small bulb shaped space above the cylinder, as the piston compressed the gasoline vapor, the spark plug would fire early so as the piston reached the top, the little chamber was shooting not just a spark but a flame thrower of burning gas which not only used up all the petro chemicals in the cylinder but also maximized the energy from it.
So today you get a lot more power from smaller engines and they are designed to last far longer (pre 70s an american car was designed for 50,000 life, today you expect 100,000 without significant repairs, and 200-250k life. A 4 or 6 banger will live longer than a 12
There have been V16s and V20s but they’re impractical for cars because they’re incredibly big, they consume a lot of fuel, and they’re mechanically complex. And there are problems where blocks that long can actually start to flex and wobble around, so you have to add a lot of heavy strengthening to them, and since the only real reason anyone would put that kind of engine in a car is for the performance, that’s kind of a no-go. V16 and V20s are still made, but for big diesel boat or train engines where the weight isn’t as big an issue.
As a lot of people have pointed out there have been in the past, but there are a lot of reasons why we don’t see them anymore.
1. We have much more efficient means of producing power now. 4 cylinder turbo charged engines (~2L of displacement) can exceed many engines from the muscle car Era of the 60s where “no replacement for displacement” was the moto and 7L+ displacements where not uncommon
2. Specifically to V style engines with large numbers if cylinders packaging is an absolute nightmare. Today’s cars don’t have the massive engine bays of the past. The more cylinders the longer the engine. This is why you see Bugatti running a W16 instead of a V16.
3. In terms of efficiency the more friction surfaces you have (in this case the interaction between the cylinder walls and scrape rings on the pistons) the more energy loss you will have to friction.
4. Weight is a huge concern as well. More weight more power needed to move the weight. Again cutting efficiency and why power adders such as turbo chargers are a better option for getting bang for the buck of energy.
To be more specific in answering your question, the reason there arent any current V16 or V20s or V24s is because of the crankshaft length. Back when there were V16s they didnt have much power. Compression was pretty low. Stress on the crank was also pretty low.
A modern V16 or V20 crank simply wouldnt be strong enough to hold up on the stress. The crank runs the length of the engine and the longer it is, the more susceptible to torsional stress it is.
This is why the Bugatti W16 works. If it were a V16 it wouldnt work, but the W16 is much more compact and the crank is much shorter than the equivalent displacement V16.
Packaging, power to weight ratio, and cost. Cost not just of the engine, but the design and production. Almost all engines are derivative and not clean sheet because tooling up a whole new line is close to a billion USD (including castings, forgings, qualification).
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