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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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.
No one here brought up the fact that turbos and super chargers change the entire equation?
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.
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.
No one here brought up the fact that turbos and super chargers change the entire equation?
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.
It depends on what you want to do with the car. If you want to go fast on a track, low weight is good and low end torque is not as important as horsepower.
If you want to haul heavy loads, a higher torque engine will move better as its usable power is in lower rpms.
Turbochargers allow you to reach higher horsepower output but require a higher rpm than a big normally aspirated engine.
And gearing in your transmission also matters. A lot of sports cars try to stay in the most usable power band of the torque curve so that is why they have more gears.
No one here brought up the fact that turbos and super chargers change the entire equation?
generally speaking, the smaller engine with same output will be working harder relative to it’s size. from a performance standpoint the smaller engine would usually be lighter and therefore the car might be faster. but an engine that’s not working as hard means it may last longer under normal usage.
so the real answer is, “it depends”
It depends on what you want to do with the car. If you want to go fast on a track, low weight is good and low end torque is not as important as horsepower.
If you want to haul heavy loads, a higher torque engine will move better as its usable power is in lower rpms.
Turbochargers allow you to reach higher horsepower output but require a higher rpm than a big normally aspirated engine.
And gearing in your transmission also matters. A lot of sports cars try to stay in the most usable power band of the torque curve so that is why they have more gears.
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