Eli5: 2 cars have the same Horsepower but different engine in terms of displacement (2.0L TDI vs 3.0L TDI) but what difference does it make and which one is better?
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The smaller displacement engine will be smaller and thus lighter, giving more power per weight. But for the same power the smaller engine needs to rev higher and/or have a higher compression ratio, both of which might have an effect on the durability / running costs of the engine.
Larger displacement engine might also have a less steep power curve, i.e. more power at lower rpm than on the smaller engine, which could be better in something like offroad or towing applications.
Well in your example, the 2.0 is a 4 cylinder engine and the 3.0 is a 6 cylinder engine. More pistons means more displacement, which means more air getting sucked into the engine for each revolution of the crankshaft, which also requires more fuel to create the proper air/fuel ratio. All of that generally means more power, and lower fuel economy. Basically, a bigger engine will make more power, over a more usable RPM range, while using more fuel.
Which is “better” depends on how you define that. The smaller displacement engine is likely more responsive and weighs less and so is likely to be the “sportier” of the two. On the other hand, the larger displacement is likely to be more reliable over the long term for the same level of power output. This is why we’re seeing a trend towards larger displacement engines with lower specific power output in trucks. A large-displacement engine with low power tends to be incredibly durable.
Which is “better” depends on how you define that. The smaller displacement engine is likely more responsive and weighs less and so is likely to be the “sportier” of the two. On the other hand, the larger displacement is likely to be more reliable over the long term for the same level of power output. This is why we’re seeing a trend towards larger displacement engines with lower specific power output in trucks. A large-displacement engine with low power tends to be incredibly durable.
This is assuming the two engines are in the same vehicle. I’m thinking the lower displacement one is likely turbocharged to make up the difference in horsepower but not necessarily. The turbo will probably have better gas mileage because a turbo setup allows the power to be used on demand where as a higher displacement engine is usually using more gas. The trade off is more engine complexity for the turbo which can translate to lower reliability and higher maintenance costs. Also there is a degree of turbo lag where the power it adds isn’t instant because the turbo has to spool up first. This lag isn’t as noticeable on smaller turbo chargers.
Manufacturers are moving more to software changes between models instead of hardware.
When a company used to do 1.4, 1.6, 1.8, 2.0, 2.5, 3.0 etc, they’ll just more to a 2.0 and a 3.0 and do them in different levels of tuning. You don’t need a huge variety of different engine blocks and parts, they’ll often share similar transmissions, and you’d only have two main “projects” on the go, rather than 5-6.
There often will be different bolt on parts, maybe a slightly smaller turbo on the lowered powered versions, maybe bigger injectors on the higher powered version, but generally they are pretty close.
Often two side-by-side versions might share all the same parts, and it’s just tuning levels in the engine ECU.
Torque tends to be related to the engine size, HP is more linked to how hard they push it and rev it too. You can always increase those by pushing them harder, but in general you’ll tend to find that the bigger engine makes more torque at lower revs.
Current “averages” are about 190hp / 420Nm from a 2.0 diesel, and 270hp/500Nm from a 3.0d. Often anything making higher figures than that tend to be classed as the more sporty models, maybe twin turbos too.
You probably will see lower powered versions as well, often with a “fake” badge on the back, like 280D on a 3.0, where they are trying to suggest they are aiming for 2.8 litre performance.
The higher powered ones might be faked upwards, BMW has 640d which is a twin turbo 3.0 diesel, so they are hinting it makes more power than a 630d. They even went all out with a triple turbo 3.0 called the M50d, to suggest you can expect 5.0 litre diesel performance.
This means you can get into a situation where a smaller engine pushed more than normal has a similar power to a larger detuned version. The detuned version will still probably have a lot more torque low down in cruising driving RPMs, 1800-2000rpm, so it’ll still feel stronger during most of your normal driving.
It’s a more lazy, less stressed engine, the torque would be more artificially limited at higher engine speeds so the maximum power ends up about the same.
It would however end up with less MPG, it’s going to be a bigger engine to lug around, more moving parts, and likely to be less efficient, but it’ll probably last longer, and less chance of something breaking.
This assumes they are engineered to a similar standard – there’s nothing to say a manufacturer could make a bigger engine, mild outputs, but really screw up on some parts and it falls to bits pretty easy. A manufacturer would probably have ranges of strength and durability targets, eg, they’ll know the power, peak cylinder pressures etc, and calculate how strong the other bits like piston rods should be. You might find those parts might be shared on all power versions, the lower ones have stuff 4 times stronger than they need to be, and the top rated ones are on the target. If they have an unusually higher powered version, they might have some one-off stronger parts just in that one model.
As a whole though, the engineering team would probably be told to make everything capable of handling say, 50% more stress than calculated, and those targets would be shared over everything they do
Going back to the 2.0d vs 3.0d, 250hp from a 2.0d would be a push, that engine would be working quite hard, but a 3.0d would do that without breaking a sweat, and you’d consider it detuned compared to what you’d expect a modern 3.0 diesel to do.
Manufacturers are moving more to software changes between models instead of hardware.
When a company used to do 1.4, 1.6, 1.8, 2.0, 2.5, 3.0 etc, they’ll just more to a 2.0 and a 3.0 and do them in different levels of tuning. You don’t need a huge variety of different engine blocks and parts, they’ll often share similar transmissions, and you’d only have two main “projects” on the go, rather than 5-6.
There often will be different bolt on parts, maybe a slightly smaller turbo on the lowered powered versions, maybe bigger injectors on the higher powered version, but generally they are pretty close.
Often two side-by-side versions might share all the same parts, and it’s just tuning levels in the engine ECU.
Torque tends to be related to the engine size, HP is more linked to how hard they push it and rev it too. You can always increase those by pushing them harder, but in general you’ll tend to find that the bigger engine makes more torque at lower revs.
Current “averages” are about 190hp / 420Nm from a 2.0 diesel, and 270hp/500Nm from a 3.0d. Often anything making higher figures than that tend to be classed as the more sporty models, maybe twin turbos too.
You probably will see lower powered versions as well, often with a “fake” badge on the back, like 280D on a 3.0, where they are trying to suggest they are aiming for 2.8 litre performance.
The higher powered ones might be faked upwards, BMW has 640d which is a twin turbo 3.0 diesel, so they are hinting it makes more power than a 630d. They even went all out with a triple turbo 3.0 called the M50d, to suggest you can expect 5.0 litre diesel performance.
This means you can get into a situation where a smaller engine pushed more than normal has a similar power to a larger detuned version. The detuned version will still probably have a lot more torque low down in cruising driving RPMs, 1800-2000rpm, so it’ll still feel stronger during most of your normal driving.
It’s a more lazy, less stressed engine, the torque would be more artificially limited at higher engine speeds so the maximum power ends up about the same.
It would however end up with less MPG, it’s going to be a bigger engine to lug around, more moving parts, and likely to be less efficient, but it’ll probably last longer, and less chance of something breaking.
This assumes they are engineered to a similar standard – there’s nothing to say a manufacturer could make a bigger engine, mild outputs, but really screw up on some parts and it falls to bits pretty easy. A manufacturer would probably have ranges of strength and durability targets, eg, they’ll know the power, peak cylinder pressures etc, and calculate how strong the other bits like piston rods should be. You might find those parts might be shared on all power versions, the lower ones have stuff 4 times stronger than they need to be, and the top rated ones are on the target. If they have an unusually higher powered version, they might have some one-off stronger parts just in that one model.
As a whole though, the engineering team would probably be told to make everything capable of handling say, 50% more stress than calculated, and those targets would be shared over everything they do
Going back to the 2.0d vs 3.0d, 250hp from a 2.0d would be a push, that engine would be working quite hard, but a 3.0d would do that without breaking a sweat, and you’d consider it detuned compared to what you’d expect a modern 3.0 diesel to do.
Your question is to vague. What are your parameters for which one is better?
You wanna talk about fuel mileage, or torque, or weight, physical size, cost to repair, part availability, warranty, etc etc.
If you wanna forget about all that or say they are both the same on all points for comparison sake, then I would at the 2.0.
For a smaller engine to make the same HP as a larger one, the smaller is more efficient, which is better.
Add in any other factory and the conversation is a different one.
This is assuming the two engines are in the same vehicle. I’m thinking the lower displacement one is likely turbocharged to make up the difference in horsepower but not necessarily. The turbo will probably have better gas mileage because a turbo setup allows the power to be used on demand where as a higher displacement engine is usually using more gas. The trade off is more engine complexity for the turbo which can translate to lower reliability and higher maintenance costs. Also there is a degree of turbo lag where the power it adds isn’t instant because the turbo has to spool up first. This lag isn’t as noticeable on smaller turbo chargers.
Which is “better” depends on how you define that. The smaller displacement engine is likely more responsive and weighs less and so is likely to be the “sportier” of the two. On the other hand, the larger displacement is likely to be more reliable over the long term for the same level of power output. This is why we’re seeing a trend towards larger displacement engines with lower specific power output in trucks. A large-displacement engine with low power tends to be incredibly durable.
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