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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It all depends on when the engines make their power. While both may have the same peak horsepower (this is how hp is measured) they may have completely different toeque curves, which matters more for drivability.
Now since you mentioned Diesel, the differences are much less important than gasoline. This is because Diesel engines tolerate much higher compression ratios than gasoline. Diesal engines also perform MUCH better under force induction than natural aspiration.
So to keep it ELI5 the simplest explanation is for diesal the engine displacement does not matter. As long as they are rated at the same they ought to consume the same amount of fuel and drive similar.
All things being equal if everyone drove at wide open throttle everywhere the engines would consume the same amount of fuel and produce the same amount of power.
All things arent equal and i dont know about you but as a professional uber driver i dont drive everywhere at wide open throttle. There are two schools of thought and I personally do not have a strong feeling either way. There are those who believe a big engine working not very hard will consume less fuel. I dont personally put much stock in that because most people speed and drive faster than engine speeds are designed for optimal fuel usage.
The other school would say more displacement more fuel consumption. This is because you can drive a small engine at low load its a smaller engine by design it requires less fuel to turn over. Less internal mass, less weight etc. In my personal experience the smaller the engine the less fuel it consumes !!!assuming part throttle driving!!! So in terms of fuel consumption either you believe that an engine with less load consumes less fuel or an engine thats smaller requires less fuel. I have not seen compelling evidence either way, but I HAVE NOT LOOKED IT UP. This is just based on my own mechanical knowledge.
If fuel consumptions not an issue for you there is no practicle difference. Some people – people who speed & drive on 2 lane highways a lot – will more appreciate the bigger engine because they “tend” to have more torque and do not have to rev as hard. Less relevant for Diesal because of the way it works. If I have a choice I will always go with a smaller engine because thats what i prefer.
Small engines being more efficent is also not the defacto case. My Imprezza had a 2l but it was so highly tuned and geared that on the highway it drank gas faster than my brothers 5.7l truck.
Imo gearing is more important than engine size. If you are interested for actual car selection drive both and do a lot of different types of driving. Not the little 4 turn fiasco dealers will take you on. Go on the freeway drive around town etc.
So which is better? For my money it is up to personal opinion. Smaller engines tend to be less popular with “normal” people because they value feel over fuel consumption. Speaking for North Americans anyway since fuel traditionally has been mega cheap. I do not like being shackled to something that costs me $100 twice a week to keep running, but i am a bit of a miser also i drive like 50,000km a year.
Grandpa always said no replacement for displacement.
The 3.0L has more overall potential than the 2.0L, even if they were stock the same horsepower the overall engine likely has more room for modifications to further improve performance.
For instance both of the above motors are turbo diesels, the 3.0L can hold more overall air and hence theoretically can hold more charged air.
A 1 PSI improvement to either motor will mean the 3.0L will have more overall power as a result.
That said, for every 10lbs of weight lost you effectively gain 1 HP (in terms of performance).
Generally speaking the smaller motors also have higher redlines than larger motors too, higher RPM = higher average power.
HP figures on motors are peak power, that value doesn’t mean much… average power does and even moreso average wheel horsepower.
If an NA motor reaches 400HP at 7200 RPM and the turbocharged vehicle reaches 400HP at 2800 RPM, the turbocharged vehicle is going to be considerably quicker because it has higher average power.
You’re getting into torque vs power territory. All things being equal, consider 1000 rabbits vs 4 horses pulling something. We can imagine that 1000 rabbits can pull the same thing about as fast as 4 horses (yea, I’m making up numbers), so they’re capable of the same peak horsepower (work per second). But can 1000 rabbits pull an RV out of the mud? That’s the torque part of the equation. What can produce the strongest rotational movement to the wheels?
Some applications really need to optimize on torque vs just total power…such as pulling and towing.
Grandpa always said no replacement for displacement.
The 3.0L has more overall potential than the 2.0L, even if they were stock the same horsepower the overall engine likely has more room for modifications to further improve performance.
For instance both of the above motors are turbo diesels, the 3.0L can hold more overall air and hence theoretically can hold more charged air.
A 1 PSI improvement to either motor will mean the 3.0L will have more overall power as a result.
That said, for every 10lbs of weight lost you effectively gain 1 HP (in terms of performance).
Generally speaking the smaller motors also have higher redlines than larger motors too, higher RPM = higher average power.
HP figures on motors are peak power, that value doesn’t mean much… average power does and even moreso average wheel horsepower.
If an NA motor reaches 400HP at 7200 RPM and the turbocharged vehicle reaches 400HP at 2800 RPM, the turbocharged vehicle is going to be considerably quicker because it has higher average power.
Generally speaking, a larger engine makes more power at a lower rpm and more torque.
A lot of it is tune. My Sprinter has the same engine as a Metris but makes 50hp less. The only difference is the tune.
Put your hands on a door knob. Hold it as right as you can. Now slowly twist it, as hard as you can! This is “torque”. Now… So the same thing, but try and turn it as fast as you can as well… This is horsepower.
So a friend of yours might have a lighter grip, but can turn it faster… Thus it offsets your tighter grip. This is horsepower.
So in really simplified terms, the higher revving am engine you have, the higher horelsepower engine you have. Versus, if you have a lower rpm engine, you have to have high torque, to equal it out.
Put your hands on a door knob. Hold it as right as you can. Now slowly twist it, as hard as you can! This is “torque”. Now… So the same thing, but try and turn it as fast as you can as well… This is horsepower.
So a friend of yours might have a lighter grip, but can turn it faster… Thus it offsets your tighter grip. This is horsepower.
So in really simplified terms, the higher revving am engine you have, the higher horelsepower engine you have. Versus, if you have a lower rpm engine, you have to have high torque, to equal it out.
Put your hands on a door knob. Hold it as right as you can. Now slowly twist it, as hard as you can! This is “torque”. Now… So the same thing, but try and turn it as fast as you can as well… This is horsepower.
So a friend of yours might have a lighter grip, but can turn it faster… Thus it offsets your tighter grip. This is horsepower.
So in really simplified terms, the higher revving am engine you have, the higher horelsepower engine you have. Versus, if you have a lower rpm engine, you have to have high torque, to equal it out.
Horsepower is a marketing number. The number that actually matters is torque. Horsepower is a measurement of torque over time and distance.
One thing a lot of people don’t realize is that you can have big fancy horsepower numbers and have them be almost entirely useless.
Your 2.0 and 3.0 examples may have the same PEAK horsepower, but where that peak is in the RPM range is going to be wildly different.
What you really want to look for is a flat “torque curve” that travels as far into the upper RPM range as possible. That is the engine that is going to give you the most all-around fun because it’ll have more available “work” at whatever RPM you’re at.
There’s a lot of other variables like vehicle weight, transmission options, etc etc etc that can make the driving experience wildly different. My 1976 280Z makes like 150 horse, but only weighs like 2600lbs after eliminating things, but the weight distribution is 50/50 and it’s agile as hell, so it’s a quick bit of fun despite not being super fast.
All things the same though, if you have a daily driver that is going to be used at all RPM ranges, and you specifically want the most available power whenever you press the go-go pedal, the larger displacement engine will give you that. It’ll cost you in terms of overall fuel efficiency, because larger displacement engines don’t tend to be pushed up the thermal efficiency ladder as much, but that’s a different consideration.
The smaller displacement engine will be able to make the same horsepower, but it’ll need higher RPMs to do it, and the RPM range where that power is is narrower.
For an extreme example, the BMW M12 for the F1 in the 80s was a 1.6 liter inline 4 cylinder that produced nearly 1400 horse power around 15000 RPMs. It made between 175 and 980 lb-ft of torque between 11k and 15k rpm. But under 11k RPM the car was virtually undrivable.
That said, you can have a little 1.8L 4 cylinder that is moderately drivable at lower RPMs but has a turbo on it so when you floor it, you’re suddenly making 300 horsepower. But the necessity of the turbo means your giggle zone is going to be narrower and higher RPM.
Horsepower is a marketing number. The number that actually matters is torque. Horsepower is a measurement of torque over time and distance.
One thing a lot of people don’t realize is that you can have big fancy horsepower numbers and have them be almost entirely useless.
Your 2.0 and 3.0 examples may have the same PEAK horsepower, but where that peak is in the RPM range is going to be wildly different.
What you really want to look for is a flat “torque curve” that travels as far into the upper RPM range as possible. That is the engine that is going to give you the most all-around fun because it’ll have more available “work” at whatever RPM you’re at.
There’s a lot of other variables like vehicle weight, transmission options, etc etc etc that can make the driving experience wildly different. My 1976 280Z makes like 150 horse, but only weighs like 2600lbs after eliminating things, but the weight distribution is 50/50 and it’s agile as hell, so it’s a quick bit of fun despite not being super fast.
All things the same though, if you have a daily driver that is going to be used at all RPM ranges, and you specifically want the most available power whenever you press the go-go pedal, the larger displacement engine will give you that. It’ll cost you in terms of overall fuel efficiency, because larger displacement engines don’t tend to be pushed up the thermal efficiency ladder as much, but that’s a different consideration.
The smaller displacement engine will be able to make the same horsepower, but it’ll need higher RPMs to do it, and the RPM range where that power is is narrower.
For an extreme example, the BMW M12 for the F1 in the 80s was a 1.6 liter inline 4 cylinder that produced nearly 1400 horse power around 15000 RPMs. It made between 175 and 980 lb-ft of torque between 11k and 15k rpm. But under 11k RPM the car was virtually undrivable.
That said, you can have a little 1.8L 4 cylinder that is moderately drivable at lower RPMs but has a turbo on it so when you floor it, you’re suddenly making 300 horsepower. But the necessity of the turbo means your giggle zone is going to be narrower and higher RPM.
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