I guess what about having extra pistons makes mpg worse vs. 1.8L, 2.5L, 3.5L, etc.?
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Small v6 engines are extremely powerful. But small cylinders like that take precision. And that takes money for assembly lines. Look at F1. And enormously powerful small displacement V6 that sips gas. Granted it is also a hybrid power plant but still, even just the ICE puts out a ton of bHP.
Smaller pistons = more friction per CC.
Same with any 3d shape.
You also have 50% more con rods, 50% longer crankshaft and cam shafts, 50% more valves, etc.
It’s a lot of extra friction and rotating mass that doesn’t gain you anything.
I’ve wondered the same thing. The best I can come up with is, the smaller you make a cylinder/combustion chamber, the greater its perimeter area (i.e. sides and top/bottom) in comparison to its volume. The air/fuel mixture doesn’t burn as efficiently as in the center of the combustion chamber, and it loses heat faster, so it winds up being better to have fewer larger cylinders than more smaller ones. Also, the more cylinders you have, the more friction you’ll have (more bearings, more piston rings, more moving parts in general), so the smaller the engine, the more you benefit from having larger cylinders.
What I’m not clear on is how the scaling works. In other words, by the same argument, wouldn’t it be more efficient to make an engine for a large ship with, say, eight giant cylinders instead of the 18, 20, 24 they actually use? Maybe the vibration would be excessive with beer-keg sized pistons, or maybe that just makes the engine more easily scaled…eight cylinders for a smaller ship, sixteen for a medium-sized one, and 24 for a large ship, all using the same size components.
Displacement is really the critical number when it comes to both power and efficiency. Going up always gets you more power and less efficiency, all else being equal.
The cylinder count and configuration doesn’t really matter that much for those things. It’s more about things like how to physically fit the cylinders into the available space, plus keeping the overall part count reasonable and the individual parts at the most practical sizes. Medium-count V engines like V6 and V8 tend to have roughly cubic overall shapes, which are generally pretty good for fitting into a car’s hood area.
Most car manufacturers traditionally made their highest power options as V6s and V8s, as that’s generally the best way to fit the maximum displacement under the hood. For lower power options, they preferred to cut the cylinder count instead of size, as it meant more shared parts and tools. So the I4 was a pretty good configuration for a lower-powered and more efficient engine option. In some cases, it might be basically a V8 with one bank chopped off. The shape isn’t the most space-efficient possible, but it still fits okay most of the time as long as the displacement stays in the same range.
The more cylinders you have, the more moving parts an engine has, which leads to increase potential for wasted energy and also increases wear and decreases life expectancy of the engine, so it’s much more smart for manufacturers to make a turbo i4 engine vs a turbo small v6 engine (same size as the i4)
The main issue is that a 6 cylinder motor with the same combined cylinder volume as a 4 cylinder motor has a lot more surface. So the ratio of surface to volume is higher in a 6 cylinder motor. The surface temperature is quite low compared to the temperature of burning fuel. Therefore, the more surface the motor has (or to be precise: the higher the surface to volume ratio is), the less efficient the fuel is burning, which gives you less power.
you are actually asking 2 questions here. a turbo forces air into the engine and allows it to burn more fuel and make more power. by itself that is no more efficient than any other engine consuming the same amount of fuel.
engines with less cylinders are more efficient because they have fewer moving parts causing friction losses and smaller cylinders burn their fuel more completely. 4 cylinders in cars are always inline, but you could make a v6 engine with smaller cylinders. this would not help because going v configuration adds complexity and more parts, so less efficient.
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