Difference between Engine sizes for a dummy :D HELP

[Anneke2013]

Ok, so as my post suggest I obviously don't have a great knowledge about vehicles.

I want to buy a "new" car but don't understand how all the bhp etc works. I prefer a bigger vehicle so always assumed you need a bigger engin to pull the car along. I've driven SUV's with smaller engins and they don't seem as powerful.

However I've been told this is no longer the case and that with modern vehicles a 1.4 or 1.6 engin is just as good. I really want a 2l+ but have also noticed manufacturers don't really do these engin sizes anymore.

So please HELP and explain in very simple terms why a 1.4l is just as good or powerful. Because after the sales lady told me I was still thinking I want the 2l+

[phil4]

They've made smaller engines more efficient.

BHP is top speed, Torque is how well it accelerates. Usually a bigger engine will give you more of both, but equally they've made smaller engines able to do what bigger engines of years ago achieved.

Combine that with weight, and a heavier car will accelerate slower regardless of the above.

There's no set rule on engine size being "required", just test drive a car, and if it feels too sluggish, get a bigger engine model, or try something from another manufacturer which is similar, but has a bigger engine.

[300bhp/ton]

phil4 said:

They've made smaller engines more efficient.

BHP is top speed, Torque is how well it accelerates. .

To someone knowing nothing about cars, this statement is completely wrong and misleading.

[StuntmanMike]

OP. What car, or type of car are you thinking of?

[300bhp/ton]

Anneke2013 said:

Ok, so as my post suggest I obviously don't have a great knowledge about vehicles.

I want to buy a "new" car but don't understand how all the bhp etc works. I prefer a bigger vehicle so always assumed you need a bigger engin to pull the car along. I've driven SUV's with smaller engins and they don't seem as powerful.

However I've been told this is no longer the case and that with modern vehicles a 1.4 or 1.6 engin is just as good. I really want a 2l+ but have also noticed manufacturers don't really do these engin sizes anymore.

So please HELP and explain in very simple terms why a 1.4l is just as good or powerful. Because after the sales lady told me I was still thinking I want the 2l+

Heavier vehicles require more power and torque to move them at the same speed as a lighter vehicle.

So generally, yes you want more power in a big vehicle.

But it is more complex than that.

Petrol and diesel engines have different characteristics as a rule. And there is also something called Turbo-charging. Which while it isn't new, is far more mainstream these days, especially on petrol engines.


A turbo 'forces' more air into an engine. And will make it perform like a much bigger engine. e.g. a 1.5 litre engine with a turbo, can be made to perform like a 3.0 litre engine without.


Turbo diesel engines are usually frugal (good on fuel) and offer a more relaxed driving technique. Meaning you don't have to drive them hard to go quickly. However they are usually slightly less refined refined and slightly slower overall.

Small petrol engines (without a turbo, small is anything under 3.5 litres really) often need to be driven hard to make them go (i.e. use all of the revs to the redline). But will normally go better than the diesels when you do this.

A turbo petrol is a bit inbetween. You won't need to drive it as hard and it will generally go better than the turbo diesels. But will use more fuel.

[iulian7]

I am sure people here will give an array of explanations as there are a lot of angles to approach this from. If you would have asked this 20 years ago, the answers would have been more straight forward.

As a generic quick answer, I would say absolute engine displacement is not that relevant for the average driver today if you are buying a new car. How much power (measured in kW and more commonly in "horse power") an engine generates is not directly tied to its displacement anymore. Aside from electric vehicles the trend is towards smaller and more efficient turbocharged engines. This is primarily due to the environment and emissions regulations.

In a simplified world you can increase power in various ways, for example:

• Increase the RPM (how quickly the engine "spins") which can be achieved for example by increasing the bore (diameter of the pistons) and decreasing the stroke (the depth/length of the pistons).
• Burning more fuel which can be done by increasing the displacement ("size" of the engine)
• Create a bigger explosion. This is what a turbocharger does. It essentially sucks in more air allowing for a bigger explosion.

There are various types of engines with different characteristics. How much power you want is up to you. What does underpowered mean to you? What has to happen when you are driving to say "oh no... this car is underpowered"?. What kind of driving do you do?

[drdino]

Engine displacement is not particularly relevant anymore when it comes to how fast a vehicle will be. What mattered back then, and still matters now is how much power/torque an engine produces. Nowadays, smaller engines can produce more power/torque due to different technologies used, therefore what is (still) important is what these figures are, broadly speaking.

[tejr]

what will be the typical use of your car? Sounds like you want an SUV.. Town biased or something that'll cope with motorways now and again?

[HazzaT]

Problem is, with turbos you can't get around the problem of low torque at low rpm in small petrol engines. SUVs/crossovers with <1.6 petrol turbos go fairly well when they're moving, but at town speeds and moving off they're incredibly sluggish because there's no boost. My folks have a 1.5TSI Karoq which is a bit of a lump at lower speeds, though once you're past 2nd it feels reasonably strong for its power output.

[Drl22]

Rather than discuss the way an engine works, which really isn’t going to help if you have little knowledge, I would suggest test driving the different engine variants of the car you want and you will know which one feels right for you.

[MikeyC]

300bhp/ton said:

phil4 said:

They've made smaller engines more efficient.

BHP is top speed, Torque is how well it accelerates. .

To someone knowing nothing about cars, this statement is completely wrong and misleading.

Which statement is 'completely wrong' (there appears to be 2 statements) ?

Maybe you could educate us as this was also my understanding ?

[phil4]

MikeyC said:

Which statement is 'completely wrong' (there appears to be 2 statements) ?

Maybe you could educate us as this was also my understanding ?

I was hoping the same, but in the longer post 300bhp/ton posted, I couldn't see any reason it was wrong or misleading. Sure, I was brief, and perhaps a bit high-level... but neither done to mislead, simply to help someone by being as brief and simple as possible.

But yes, please do let me know where I went wrong, always helps to to know how you've screwed up so you can avoid in the future.

[Roboticarm]

I'd suggest an alternative way to look at it is to ignore the engine size and bhp and simply look at the stats.
Parkers and other sites tend to hold the 0-60, top speed, mpg and other key statistics for most cars.

If the acceleration mpg etc all suit your needs then go and test drive. Some cars feel faster than the stats suggest other slower. I always find that the extra shove of a turbo adds to the feeling of acceleration.

But as mentioned above, some of the latest engines are putting out some surprising numbers, 3 cylinder 1 litre cars pushing out the sort of bhp and 0-60 a late 90s 2.0 was doing

[HazzaT]

phil4 said:

I was hoping the same, but in the longer post 300bhp/ton posted, I couldn't see any reason it was wrong or misleading. Sure, I was brief, and perhaps a bit high-level... but neither done to mislead, simply to help someone by being as brief and simple as possible.

But yes, please do let me know where I went wrong, always helps to to know how you've screwed up so you can avoid in the future.

Horsepower is the actual work done by the engine over a certain time (or rate, in this case rpm). Torque is the turning moment the engine is exerting on the crank, imagine the engine is a bloke working a lever. Therefore, horsepower=torque x rpm/constant, in this case the constant is 5,252. This will produce a graph of power the engine is producing at a given rpm. So yes, while a car with an engine that produces max torque from say 1500rpm will probably accelerate from 1500rpm faster than one with an engine that produces the same max torque at 5000rpm, it's not really correct that the torque figure is the reason for the acceleration. The area under the horsepower line on the graph is the most important thing.

EDIT: also not really related to top speed, final drive ratio and aero are just as important as power for that.

[Baldchap]

Torque is how hard you can turn something - rotary force. In simple terms, BHP is a mathematical representation of torque * revs.

Neither tells us about acceleration or top speed without more information.

Test drive what you are interested in and don't worry about the geeky stuff if that isn't your bag.

[phil4]

HazzaT said:

Horsepower is the actual work done by the engine over a certain time (or rate, in this case rpm). Torque is the turning moment the engine is exerting on the crank, imagine the engine is a bloke working a lever. Therefore, horsepower=torque x rpm/constant, in this case the constant is 5,252. This will produce a graph of power the engine is producing at a given rpm. So yes, while a car with an engine that produces max torque from say 1500rpm will probably accelerate from 1500rpm faster than one with an engine that produces the same max torque at 5000rpm, it's not really correct that the torque figure is the reason for the acceleration. The area under the horsepower line on the graph is the most important thing.

EDIT: also not really related to top speed, final drive ratio and aero are just as important as power for that.

Thanks, I was trying to keep it short and simple And yes, I did already know most of the above, I was, as I say, trying to keep it short and simple.

[Wooda80]

Given that the OP appears to be a fairly typical car user looking to buy a new car, most of the comments on this thread are a good example of why someone who says "I know a lot about cars" doesn't necessarily make a good car salesman

[HustleRussell]

OP, test drive the cars on the kinds of roads you will use them on and decide which model you need. You don't need to get technical on this.

[HazzaT]

Wooda80 said:

Given that the OP appears to be a fairly typical car user looking to buy a new car, most of the comments on this thread are a good example of why someone who says "I know a lot about cars" doesn't necessarily make a good car salesman

Spinny thing that goes woosh make the small engine go vroom better than big engine without spinny thing

That better?

[phil4]

HazzaT said:

Spinny thing that goes woosh make the small engine go vroom better than big engine without spinny thing

That better?

If you changed a couple of the words to sound less like talking to a 3 year old... I think you've pretty much nailed it!