'Right' cylinder volume

'Right' cylinder volume

Author
Discussion

diluculophile

Original Poster:

130 posts

250 months

Thursday 27th August 2015
quotequote all
Is there an optimal cylinder size with regards to power/torque output and fuel usage?
Is it affected by the presence or absence of turbochargers or superchargers?

Slightly frivolous thread, I know, but for some reason 500cc's seems appropriate:

V-Twin sportsbikes should be 1000cc right?

2 litre 4 pots like that in a RenaultSport Clio RS200 (not the new one) hit the spot

Straight and V6's of about 3 litre displacement? I'm thinking BMW 330i/335i

4.0 V8? - BMW M3 E92, recent Mercs with a twin turbo?

6.0 V12 - Astons.


I'm willing to consider 'as big as possible' as a reasonable argument smile

Discuss...

Jacobyte

4,718 posts

241 months

Thursday 27th August 2015
quotequote all
I read many years ago that 400cc is the optimal swept volume for most efficient combustion in a 4-stroke engine. I can't recall the source though.

diluculophile

Original Poster:

130 posts

250 months

Thursday 27th August 2015
quotequote all
Jacobyte said:
I read many years ago that 400cc is the optimal volume for most efficient combustion in a 4-stroke engine. I can't recall the source though.
I'm wondering whether that has changed with recent technology - turbo's etc. and the habit of manufacturers downsizing engines.

lostkiwi

4,584 posts

123 months

Thursday 27th August 2015
quotequote all
I always remember Daihatsu claiming the optimal cylinder size was 331cc when they released the 993cc Charade.

Twin2

266 posts

121 months

Thursday 27th August 2015
quotequote all
It's difficult to say but there must be a ton of research papers out there on this.

My guess is that the optimum sizes will be more to do with the squareness of the volume.

stavers

251 posts

145 months

Thursday 27th August 2015
quotequote all
diluculophile said:
Is there an optimal cylinder size with regards to power/torque output and fuel usage?
Is it affected by the presence or absence of turbochargers or superchargers?

Slightly frivolous thread, I know, but for some reason 500cc's seems appropriate:

V-Twin sportsbikes should be 1000cc right?

2 litre 4 pots like that in a RenaultSport Clio RS200 (not the new one) hit the spot

Straight and V6's of about 3 litre displacement? I'm thinking BMW 330i/335i

4.0 V8? - BMW M3 E92, recent Mercs with a twin turbo?

6.0 V12 - Astons.


I'm willing to consider 'as big as possible' as a reasonable argument smile

Discuss...
In an single word - no.

The problem, as with everything to do with engineering, is one of compromise. The ideal cylinder for getting power out of is rubbish for bottom end torque and fuel consumption.

I think it's generally accepted that the best compromise is somewhere around 400cc - 500cc per cylinder with an undersquare (longer stroke than bore) design to keep heat loss through the cylinder wall at a minimum whilst allowing enough bore diameter to squeeze the valves/spark plug/injector in at the top.

These struggle to rev highly, mainly due to piston speed, so peak power is not as good as something with an oversquare design (F1 engines being practically the ultimate example) but torque is generally better - especially low down.

Fiat are around this size (which is why their 1L engine is a twin), BMW (hence a 1.5L 3 cylinder, 2.0L 4 cylinder, 3.0L 6 cylinder), VAG etc.. Where they want more power with larger they can compromise on this as the balance can swing away slightly from fuel consumption but probably share a similar bore so as to commonise as many of the top end components as possible.

TooMany2cvs

29,008 posts

125 months

Thursday 27th August 2015
quotequote all
What DID Ferrari know with the 250cc-per-cylinder 3.0 v12, anyway?

300bhp/ton

41,030 posts

189 months

Thursday 27th August 2015
quotequote all
diluculophile said:
Jacobyte said:
I read many years ago that 400cc is the optimal volume for most efficient combustion in a 4-stroke engine. I can't recall the source though.
I'm wondering whether that has changed with recent technology - turbo's etc. and the habit of manufacturers downsizing engines.
Not all engines have been downsized. It's just there is maybe a wider range of smaller engines these days. But 1.0 litres engines weren't exactly rare or unheard of 20-25 years ago.

Edited by 300bhp/ton on Thursday 27th August 15:02

CanAm

9,115 posts

271 months

Thursday 27th August 2015
quotequote all
300bhp/ton said:
Not all engines have been downsized. It's just there is maybe a wider range of smaller engines these days. But 1.0 litres engines where exactly rare or unheard of 20-25 years ago.
I take it you meant to say "But 1.0 litres engines weren't exactly rare or unheard of 20-25 years ago."

lostkiwi

4,584 posts

123 months

Thursday 27th August 2015
quotequote all
300bhp/ton said:
Not all engines have been downsized. It's just there is maybe a wider range of smaller engines these days. But 1.0 litres engines where exactly rare or unheard of 20-25 years ago.
Really?

There dozens of them. Mini, Fiat Uno, Daihatsus, Micras, Peugeot 104, small Renaults etc.... There were dozens of them - they just weren't a lot of fun to drive in the main.

300bhp/ton

41,030 posts

189 months

Thursday 27th August 2015
quotequote all
CanAm said:
I take it you meant to say "But 1.0 litres engines weren't exactly rare or unheard of 20-25 years ago."
Thanks, yes and edited smile

lostkiwi

4,584 posts

123 months

Thursday 27th August 2015
quotequote all
300bhp/ton said:
CanAm said:
I take it you meant to say "But 1.0 litres engines weren't exactly rare or unheard of 20-25 years ago."
Thanks, yes and edited smile
Ah that makes more sense then smile

LordGrover

33,531 posts

211 months

Thursday 27th August 2015
quotequote all
Toyota/Subaru tried to create hype with the GT86/BRZ engine; c. 2.0 litre, 4 cylinder, 86mm dia x 86mm stroke, boxer engine.
It's a good enough engine but by no means special producing c. 190 BHP and 150 lbs.ft and not terribly economical.

300bhp/ton

41,030 posts

189 months

Thursday 27th August 2015
quotequote all
LordGrover said:
Toyota/Subaru tried to create hype with the GT86/BRZ engine; c. 2.0 litre, 4 cylinder, 86mm dia x 86mm stroke, boxer engine.
It's a good enough engine but by no means special producing c. 190 BHP and 150 lbs.ft and not terribly economical.
That'll be 197bhp DIN and 151 lb ft. Which is pretty much class leading today and only a few production engines have produced better specific outputs.

Seriously, what 2.0 litre n/a engines produce more power, or even match this today?


GT-86 197bhp 151lb ft
EP9 Civic Type R 197bhp 145 lb ft


In fact, what naturally aspirated 2.0 litre has ever produced more torque??

Edited by 300bhp/ton on Thursday 27th August 15:47

GroundEffect

13,819 posts

155 months

Thursday 27th August 2015
quotequote all
Remember a lot of this is dictated by the various tax rules around the world.

For instance, 1.5 litre is an important threshold for China therefore you are seeing a lot of 1.5 litre engines coming out.

Luther Blisset

391 posts

131 months

Thursday 27th August 2015
quotequote all
Except no 86 makes the numbers on a dyno.

300bhp/ton

41,030 posts

189 months

Thursday 27th August 2015
quotequote all
Luther Blisset said:
Except no 86 makes the numbers on a dyno.
What kind of dyno?

EDIT:

Figures seem fine here:
http://www.ddperformanceresearch.com/forum/viewtop...

Edited by 300bhp/ton on Thursday 27th August 15:54

RobinBanks

17,540 posts

178 months

Thursday 27th August 2015
quotequote all
GroundEffect said:
Remember a lot of this is dictated by the various tax rules around the world.

For instance, 1.5 litre is an important threshold for China therefore you are seeing a lot of 1.5 litre engines coming out.
For that same reason you saw relatively more new average cars which were 1.5 litres or lower in the 1990s in the UK than now. Whereas now there's no tax advantage to being 1549cc or below.

GroundEffect

13,819 posts

155 months

Thursday 27th August 2015
quotequote all
RobinBanks said:
GroundEffect said:
Remember a lot of this is dictated by the various tax rules around the world.

For instance, 1.5 litre is an important threshold for China therefore you are seeing a lot of 1.5 litre engines coming out.
For that same reason you saw relatively more new average cars which were 1.5 litres or lower in the 1990s in the UK than now. Whereas now there's no tax advantage to being 1549cc or below.
Watch the next couple of years wink

R8VXF

6,788 posts

114 months

Thursday 27th August 2015
quotequote all
RobinBanks said:
GroundEffect said:
Remember a lot of this is dictated by the various tax rules around the world.

For instance, 1.5 litre is an important threshold for China therefore you are seeing a lot of 1.5 litre engines coming out.
For that same reason you saw relatively more new average cars which were 1.5 litres or lower in the 1990s in the UK than now. Whereas now there's no tax advantage to being 1549cc or below.
Even better when the new tax rules come in smile