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What is the advantage of smaller engines?

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Old Jan 23rd, 2019, 11:03   #1
Harvey1512
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Default What is the advantage of smaller engines?

As per the title really but a bit of background first.

A few years ago I took a 1.6d V60, believing the hype about new, better, more economical engines. It was fine on the flat but the moment you put it on an incline with passengers the engine had to work like stink and long journeys gave me a headache. After 2 yrs I was happy to give it back, economy worked out around 44-46mpg

After that car I went to a 2.0d XC60, managed the same economy, driving was a pleasure though. I'm now in a 2.0d Superb, auto, I get 50-52mpg and long journeys are even easier. Small engine being more economical my foot.

Yesterday my car was getting serviced and I was given a courtesy car, a petrol Octavia estate, auto. It was a fabulous drive, fast off the mark, auto was seamless, calm and quiet. I asked the service guy when I returned it what engine size it was, expecting 2.0. It was a 1.0 litre petrol. Stunning, absolutely stunning.

The question is though, what benefit does the smaller engine give in real terms? I don't mean theoretically in a lab as my V60 showed what nonsense that was. Would me moving to a 1.0 petrol really be better? I don't have an ego on this, I don't feel the need to boast about engine size, but I would like to understand the genuine benefits of downsizing engines. I might have no choice moving forwards but the practical reasons would be good to know.
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Old Jan 23rd, 2019, 12:07   #2
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There's a matter, as you have identified, of real vs "lab test" benefits.

The REAL benefits of smaller engines, such as the 1.0 3-pot turbo in the octavia, are simply lower weight and less frictional loss (fewer cylinders). These are not contentious.

Petrol combustion depends on there being the correct amount of fuel and air (stoichiometric ratio) for complete combustion. The amount of fuel you burn gives you your power output, and the more air you can force into the cylinder (ie turbo) gives you the ability to burn more fuel.

The real question then becomes the thermal efficiency of the engine. Frictional losses can be included in that, but the claims of efficiency in turbocharged engines CAN be contentious. Manufacturers can write software that keeps the engine performing at its most efficient in unrealistic lab test scenarios (like the old NEDC fuel economy tests, where acceleration was 0-30mph in 27 seconds), but offer much more power (and thus burn more fuel) when you put your foot down in the real world.

Another approach (and one that has much better real-world results) is the use of faux-atkinson cycle. An otto cycle engine compresses the fuel/air charge, ignites it and expands it again. An Atkinson cycle engine expands the charge more than it was originally compressed - a proper atkinson engine has a very "interesting" crank setup to do this. Toyota typically implement faux-atkinson on their hybrids (like my GS) - the valves close late, so the compression stroke has already begun and some of the charge (air, since it's a direct injection engine) is pushed back out of the cylinder. The valves then close and the charge is compressed by the typical ~10:1, ignition occurs and the expansion is in the region of 13:1. This directly harvests more energy (and the end goal is to expand the charge until it reaches 1 atm pressure).

So, to summarise, for a given thermal efficiency the smaller engine has benefits in weight and friction (but the latter may mean that by default the thermal efficiency is slightly improved). Otherwise, for the same power output the same amount of fuel must be burned.
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Old Jan 23rd, 2019, 12:29   #3
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I have no experience on more recent 'small' engines, 'Harvey1512', but my own experience suggests that, personally, there is little benefit.

This even goes back to when a Cortina 1.6, driven like for like could be more economical than the 1.3 engined version. Similarly, I once owned an original Fiat 500 which returned 47 MPG overall, while my Mini 1000 managed 49.

I prefer large, lazy engines and am prepared to pay any fuel penalty, especially as I now do a very small annual mileage. Larger engines are also less stressed and therefore more relaxing to drive than a 'buzz box'. My Fiat, particularly, would scream at high revs when pressing on (50 MPH!!) on account of the low gearing required to propel a (nominally) four seater car on such a small engine. On the other hand, I could easily remove the engine and take it indoors to work if necessary!

Maybe modern small engines are better today, but I still prefer our 2 and 3 litre cars to a friend's 1 litre Fiesta.

Fuel consumption aside, I would normally expect a smaller engined car to be less expensive to insure than one with a larger engine, although that is not always the case.

A large engine will also cost more to repair than a small one when the time comes (6 pistons to replace instead of 4, for example), but that may not be a consideration if you have a company vehicle.

I'm sure that there are many other factors, but at the end of the day it comes down to personal preference and I would not attempt to influence anybody differently.

Regards, John.
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Old Jan 23rd, 2019, 12:41   #4
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I-S, a very thorough post but I didn't understand a word of it

John, I am generally in your camp but I am open to learning, not saying you are not by the way, as we are being pushed this way. The Octavia I had was massively helped by being an auto as I had no need to make hundreds of gear changes, the car did it for me and without me realising. That was my experience in my V60, I was constantly changing gear and on a long drive my left leg was aching.
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Old Jan 23rd, 2019, 12:43   #5
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I have the same experience. Fiat 500s and minis. Small box carrying 2 adults and possibly 2 children. No luggage space, narrow tyres on small wheels, tiny petrol tanks. Not good at going fast.

Bigger engines, bigger box. More doors, more space for more adults. Bigger tank for longer distances and room for luggage. Less stressful to drive, less stress on components. Similar mpg but better longevity.

Bigger should be safer?????
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Old Jan 23rd, 2019, 13:09   #6
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An interesting comparison could be the V60 Polestar.

The earlier models had a 3.0-litre inline 6 with 350bhp and 6 speed auto.

The later models had a 2.0-litre inline 4 with 367bhp and 8 speed auto.


Which would you rather have?
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Old Jan 23rd, 2019, 13:11   #7
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Engines these days are incredible. The 1.0 ecoboost Ford can fit on an a4 piece of paper yet can put out 150hp and more in some guises. I have long been a fan of small engined having run various smart cars and the like but the technology is frightening. No longer are home repairs an option unless you are a well trained mevhanic/engineer/surgeon. The 1.5d engine in the mini I have just bought puts out anything from 90hp to 150hp, and can be mapped to just over 200, from a 1.5 diesel!!!


Edit, I remember keke rosberg being interviewed about the blown 1500cc four pot F1 days when cars could put out 1500hp in 'hand grenade qualifying spec'...he said there was no throttle control, the power delivery was like flicking a light switch, on or off!!

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Old Jan 23rd, 2019, 13:15   #8
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Quote:
Originally Posted by john.wigley View Post
I prefer large, lazy engines and am prepared to pay any fuel penalty, especially as I now do a very small annual mileage. Larger engines are also less stressed and therefore more relaxing to drive than a 'buzz box'.
I have to confess that that is my feeling as well.

Back in the past, I was an independent driving instructor and, because they were so 'popular' in the trade, I went for a Vauxhall Corset... sorry, Corsa... as well. And, being naive, I went for the 1-litre 3-cylinder jobby. Uncomfortable and needing to change down for slight inclines on motorways soon showed me the error of my ways!

That put me off small cars big time!

Having 'seen the light' I did, for a quite a while run a Nissan Almera 1.6 (which all the pulis loved) and then upgraded to a 1.8 Sport as a training car. I loved that - and so did my pupils including those had been in the 1.6 up until the changeover. On a quiet road, I would let all pupils see how that bit more power made life easier - especially those who started learning in the 1.8. The 1.8 Sport was a fantastic car. A tour of France for a fortnight reinforced the feelings as well. All comfortable and easy.

From there, I went to a national driving school which ran on Ford Focuses (or whatever the plural may be. Foci?) I wasn't particularly impressed.

Retirement came, and so did my first V70 automatic (Ph 1) - a 2nd-hand one I had been promising myself that I would buy when I retired. SWMBO was not impressed with the idea; but, by that time had come, we were no longer together. That power being applied smoothly was the bees-knees. And the comfort, after all the cars I had in the past, was pure bliss.

After 3-4 years (?) I flogged that coz I bought a C70 (plain clothes GT version) automatic convertible. Again, the comfort and the power (OMG!!!) did mean slightly higher petrol bills; but in my mind (feeble and tiny as it is) I was quite happy with my purchase and happy to have slightly higher fuel bills.

In summary. For me, it has to be a large car with a large engine that doesn't need to work hard all the time. And any time I ponder the point, I think of my big, comfy and smooth Volvos.
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Old Jan 23rd, 2019, 14:02   #9
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Quote:
Originally Posted by biggbn View Post
Engines these days are incredible. The 1.0 ecoboost Ford can fit on an a4 piece of paper yet can put out 150hp and more in some guises. I have long been a fan of small engined having run various smart cars and the like but the technology is frightening. No longer are home repairs an option unless you are a well trained mevhanic/engineer/surgeon. The 1.5d engine in the mini I have just bought puts out anything from 90hp to 150hp, and can be mapped to just over 200, from a 1.5 diesel!!!


Edit, I remember keke rosberg being interviewed about the blown 1500cc four pot F1 days when cars could put out 1500hp in 'hand grenade qualifying spec'...he said there was no throttle control, the power delivery was like flicking a light switch, on or off!!
I’ve seen one of those, 1500cc and a big turbo. So I asked.... Soooo, how long does this last? Ohhhh about 75-90 mins depending on how hard you drive it then it’ll need a rebuild 😂😂😂

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Old Jan 23rd, 2019, 14:06   #10
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The smaller the engine, the less volume, therefore less capacity for fuel to burn.

As you’ve found out the more weight the engine has to move (more passengers/luggage combo) the closer to the upper limit the smaller engine has to work to overcome the rolling friction. No surprises so far.

Did you know traveling on a level road, maintaining a constant speed, only needs around 20bhp so having an engine that can produce 300+bhp is a bit of a waste. The problem is getting to the rolling speed you also need to overcome the air drag. There is 4 times as much drag at 60mph as 30mph and that needs power = burn fuel to get there. Again, no surprises from Professor Physics.

Coming back to my opening sentence, we are in an age where air pollution is the main agenda and anything to reduce the volume of fuel burned must be good. The problem is we are tied into CO2 emissions which favour diesel BUT diesel is bad and petrol is viewed as less bad in terms of particle matter emissions but less good in terms of CO2. So, in my roundabout way, we arrive at if you must burn fuel burn it in a lower volume.

Back in the real world you have a fully loaded car weighing 1.5+ tonnes with all the safety equipment plus a 5-600kgs payload. You need to burn fuel to make power to make it move regardless of the swept volume of the engine burning the fuel.
A smaller volume cannot burn as much fuel therefore cannot make as much power taking longer to get to the required speed.

Reduce all speed limits to 30 mph and performance difference between a 5.0 V8 muscle car and a 900cc twin is less significant.
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