[Guna]

I dont know if my observation is right, I have felt that engines with bigger capacity keep the momentum better. This could be simply beacuse of better torque available but heavier roating parts may have some role.

[longhorn]

To sum it up, I would say that although engine size does matter, the gap is fast closing and it does not matter as much as it used to matter, say 20 years ago. With the advancement in technologies, the specific output of a motor is much higher than what it used to be, without too much of a compromise on engine life. Hence even though the output of a higher capacity motor is still better that that of a lower capacity one, other things being equal, the requirement to up the displacement of an engine to extract more power has been considerably reduced from what used to be required in the past. Now we are able to extract the same amount of power and torque from lower capacity motors without compromising on the important factor of engine life and its reliability.

[Shan2nu]

I dont know if my observation is right, I have felt that engines with bigger capacity keep the momentum better. This could be simply beacuse of better torque available but heavier roating parts may have some role.

I guess it has to do with the torque or rather the torque to weight ratio.

Coz even if bigger engines use heavier parts, these engines have an equally big displacement to overcome this rotational momentum.

So if a 2ltr engine with a 10:1 comp ratio uses a 10kg flywheel and a 4ltr engine with 10:1 CR uses a 20kg flywheel, there wont be much of a diff in the way these engines keep up their momentum (based on rotational mass alone).

To sum it up, I would say that although engine size does matter, the gap is fast closing and it does not matter as much as it used to matter, say 20 years ago. With the advancement in technologies, the specific output of a motor is much higher than what it used to be, without too much of a compromise on engine life. Hence even though the output of a higher capacity motor is still better that that of a lower capacity one, other things being equal, the requirement to up the displacement of an engine to extract more power has been considerably reduced from what used to be required in the past. Now we are able to extract the same amount of power and torque from lower capacity motors without compromising on the important factor of engine life and its reliability.

Well, i wouldn't say that the gap between big and small engines has reduced. Any technology that can be used on small engines to boost its power can be used on a bigger engine as well.

What actually has changed is an engine's ability to cater to a certain bhp/torque requirement without having to increase its displacement. The smaller engines cannot compete with bigger engines for outright power.

But a 2ltr engine producing 200bhp is lighter, more fuel economical and less space occupying than a 4ltr engine producing the same 200bhp. This is why manufacturers prefer smaller engines.

Shan2nu

[CPH]

Originally Posted by sidindica

While today's tech makes displacement seem redundent, I think that there is no replacement for displacement, especially between AMG, M division and RS quattro GMBH motors, all 5.0L plus with very high hp.

Quattro and M Power are a league apart from AMG. The reason why AMG is producing such engines is because there is still demand for these engines at this moment in time even if it is sharply declining.

Displacement is not the answer for everything. The American way to go about power is to go massive. But this is hardly the engineering solution.

An incredible car to drive is the SR8. It is only powered by a normally aspirated 2.8 V8 but holds the lap record at the Nürburgring at 6:48 for the 20.6km.

The Viper SRT-10 with a massive engine needed 34 seconds more.

The MC12 and the Zonda F Clubsport needed over 36 seconds more.

The Corvette ZR1 was another 2 secenonds slower.

It is more likely the package that counts than the displacement.

[longhorn]

Originally Posted by Shan2nu

The smaller engines cannot compete with bigger engines for outright power.
Shan2nu

This is not true. The HM amby with a 1800 cc Isuzu petrol engine produces only 75 bhp while the 1200 cc K12M Ritz motor produces 84 bhp. That's a solid 9 bhp hike despite a deficiency of 600 cc ! It all depends on the technology that goes into building these motors. With the right tech, you can produce better outright power than a higher displacement engine from a lower cc motor. Of course, if the same tech was applied to the higher cc engine, it would give better output than a lower cc motor !

[supremeBaleno]

Originally Posted by longhorn

Of course, if the same tech was applied to the higher cc engine, it would give better output than a lower cc motor !

I think that's where the "all other things remaining the same" part comes in.

Originally Posted by breezydrive

I drove bro-in-law's Ritz Zxi (1.2 K-series) for a 250 km round trip on NH-1, seemed silken smooth in all gears uptil 120 kmph but no compaison with Swift Vxi (1.3) beyond 120 kmph.

I agree. We have the Swift-P and for normal driving, I never liked the car - frequent gear changes, sluggish acceleration (esp. in 3/4/5 gears). Kerala highways are not safe to drive above 120kmph - so not sure how it is at those speeds.

Recently I got to drive my friends Ritz-P in Chennai and was floored by the drivability of the car - pure pleasure. Anyday better than our Swift which has 100cc more displacement.

P.S. : My observations with the Swift are w.r.t. the Baleno which is my regular car.

[Shan2nu]

Of course, if the same tech was applied to the higher cc engine, it would give better output than a lower cc motor !

Thats what i'v been saying, from my very first post.

You can't compare a well tuned small engine with a hopeless big block and say the gap has been reduced. Compare the most powerful small engine with the most powerful big engine.

A top fuel 1.3ltr drag bike does around 1000bhp (same as the 8ltr Veyron engine). But this doesn't mean a 1.3ltr engine has caught up with a 8ltr engine, coz only when you compare this bike engine to a 8ltr top fuel dragster doing 7500bhp, do you realise how big the diff really is.

Shan2nu

[jaaz]

[quote=sidindica;1697714]While today's tech makes displacement seem redundent, I think that there is no replacement for displacement,

A little known but interesting fact is that the 7.0L LS 7 in the ZO6 can return 16mpg city and 26 mpg highway (according to US driving cycle) and despite producing 505 bhp, it evades the 2,500 $ federal gas guzzler tax.

I'm curious to know - Whether Large displacement means more apetite for Fuel. I mean - Whether a 3 Cylinder and 4 cylinder engines generating equal power deliver the same fuel efficiency?

[Shan2nu]

I'm curious to know - Whether Large displacement means more apetite for Fuel. I mean - Whether a 3 Cylinder and 4 cylinder engines generating equal power deliver the same fuel efficiency?

Again, there are 2 ways of looking at this. A race/drag tuned small engine will def guzzle more fuel than a bigger engine, tuned for economy. But if both engines are perfomance tuned to the same extent, the bigger engine will be less economical.

Check out "Variable Cylinder Management" which allows a big engine to shut down some of its cylinders during low load situations to increase fuel economy and lower emission levels.

Then there are thousands of other factors affecting FE related to frictional and aerodynamic resistance like engine speed, gearing, tyre pressure, COD, weight etc to name a few.

Shan2nu

[DocG]

too much argument over a simple issue..

I'll sum it up to personal preference. India is a fledgling car market, and most people are retards in that the first question asked is "Average kya hai" (What's the FE).

If a 1200CC engine is generating 80+ Hp, rest assured that most drivers will never ever use it to it's potential. Simple fact is that people drive for KMPL and not performance, so no redlining, no slick shifting etc...

If it were me, gimme that big block V8 and I'll be hella happy!
The guy down the street though wants 22KMpL so he bought the Nano

It's not all just about performance figures! Most people chirping about this did that at the nurbergring etc and about how fast a lap time was have never driven a big block V8!

Try it, the character of that thing at idle will have you more pleased than a tin can at 180 KMPH

[longhorn]

American muscle cars are all for brute power. They produce all that massive power by just upping the cc and producing V8 and V 12 engines. They are not known for their reliability/handling. Germans are much better at this.They produce better engines than the yankees. IMO the Japanese are the real masters of this game. The know how to squeeze out power from every square inch of their cylinders. They produce reliable engines and lower capacity motors with higher output though their cars are not as comfortable to travel in when compared to the yankees and Germans.

[vkarulkar]

Originally Posted by longhorn

American muscle cars are all for brute power. They produce all that massive power by just upping the cc and producing V8 and V 12 engines. They are not known for their reliability/handling. Germans are much better at this.They produce better engines than the yankees. IMO the Japanese are the real masters of this game. The know how to squeeze out power from every square inch of their cylinders. They produce reliable engines and lower capacity motors with higher output though their cars are not as comfortable to travel in when compared to the yankees and Germans.

+1 for that. American muscles are famous for big size and big engines. germans for reliability and optimization. Japanese for best resource utilization, manouvarability and handling.

[r@CYR@y]

[quote=jaaz;1700565]

Originally Posted by sidindica

I'm curious to know - Whether Large displacement means more apetite for Fuel. I mean - Whether a 3 Cylinder and 4 cylinder engines generating equal power deliver the same fuel efficiency?

There are 2 more ways which you should look at..

1. Are you increasing the engine size by increasing the number of cylinders
for eg inline 3 or 4 or 6 or V6 or V8 etc
2. Are you increasing the cylinder size by increasing the bore and stroke.

Fuel is burnt more efficiently in small cylinders compared to large cylinders because of less amount of oxygen is utilized completely whereas in larger disp cylinders it takes considerable time for complete combustion, till then the exhaust valves will be open and the unburnt oxygen and fuel is not utilized.

So, If we want better fuel efficiency and more power in a fixed engine size we should increase the number of cylinders..

Increase in the number of cylinders also reduces the vibration in the engine and the engine revvs freely..

[supremeBaleno]

Originally Posted by DocG

most people are retards in that the first question asked is "Average kya hai" (What's the FE).

"Retards" is a little too harsh. Forget "average" which is a NI slang, just look at the term 'FE'. The 'E' stands for 'Efficiency', which IMHO is a great thing to have. If you have an efficient engine, that IMO is great.

Originally Posted by DocG

If a 1200CC engine is generating 80+ Hp, rest assured that most drivers will never ever use it to it's potential. Simple fact is that people drive for KMPL and not performance, so no redlining, no slick shifting etc..

I drive a 91bhp car, which is known to be a driver's car. But where in the city (Chennai) do I use it to it's potential ? I drive 40kms a day, of which, the only stretch where I could unleash it's potential is the 4kms on the MadhyaKailash-TIDEL stretch. But again, it is not easy given that 2-wheelers are on each of the 3 lanes.

[thermalpaste]

TO begin with, lets define horsepower and 'Torque'. Torque produced at the crank is called a 'moment' since it rotates on an axis. An imaginary line across the 2 ends of a crank is the axis.

Torque in this case is Force X Perpendicular distance.

Long stroke engines have more perpendicular distance and a relatively smaller bore.
Force or combustion is what drives the piston down. So Torque characteristics can vary on identical engines with different piston face designs, number of valves and compression ratio and so on.
However, it's not necessarily true that only long stroke engines produce more torque. You could have a short-stroke engine producing more torque than a long-stroke or a square engine. But it's always true that the torque characteristics would greatly vary between the 2 aforementioned engines -- the long stroke would typically produce more torque at lower rpms.
There is more friction in long stroke engines as pistons need to travel a greater distance per stroke. Also, smaller or restricted head-design would limit the speed of a long stroke engine as compared to a short-stroke engine. It is mostly true that a short-stroke engine will allow higher engine speeds as compared to long stroke engines.

Now talking about James Watt's definition of horsepower, 1 HP is equivalent to vertically lifting 33 pounds of mass upto 100 feet in one minute.

You can imagine a 1 HP elevator 'A' that travels hundred feet up and can only carry 33 pounds and takes 1 minute to reach a hundred feet.

Another elevator 'B' travels 1 feet up and can carry 3300 pounds and takes a minute to reach 1 foot from where it started originally. Both elevators produce exacctly 1 HP.

1 HP = no of feet travelled by the elevator vertically X Mass = 33000 Foot Pounds.

Lets take rotational forces into consideration.

Eg. 1 :

1 HP = circumference in feet X Mass

If the circumference of a flywheel is 10 feet and 100 pounds of force is applied to rotate the flywheel, the flywheel moves at :

[(1 HP / Circumference) / Force]

= (33000 / 10) /100 = 33 RPM


Eg 2 :

If the circumference of the flywheel is 65 feet and 100 pounds of force is applied to rotate the flywheel, the flywheel moves at:

[(1 HP / Circumference) / Force]

= (33000 / 65) /100 = 5.076 RPM


Yet both produce the same Horsepower at different RPMS !

We all know that circumference = pi*d = 2*pi*r

Circumference is nothing but the distance travelled by the flywheel to complete a revolution.

Horsepower = (Torque * RPM) / (33,000 / 2* pi)

= Torque X RPM / 5252


The last equation just shows us that RPMs have a lot to do with Horsepower too. There is such strong correlation with horsepower , torque and RPM.

To conclude : It doesn't matter what the displacement of the engine is, what matters is the way the engine produces power, the way the power is delivered to the wheels (taking frictional losses into consideration) and the number of gears + gearing rations for the vehicle.

For vehicles with a really narrow power-band (eg: Volvo buses) it makes sense to have 6-7 gears.