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?
In: 87
Horsepower and engine size don’t account for gear ratios, turbo/super charging, or importantly, weight.
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.
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.
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.
Engines can be rather complex, and there’s a number of factors that go into which engine is “better” which is pretty arbitrary to begin with. One engine might be more efficient (which can be considered “better” even if it’s slower. One might be more powerful/faster (“better”). One might be lower displacement and turbocharged, one might be more reliable (cheaper is “better” too).
Now specifically to the two engines you mentioned, one has more horsepower than the other unless you’re comparing different years, so could you provide a different example?