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Old 1st February 2010, 16:19   #46
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With the amount of engineering that has gone in, it is not a surprise to see higher specific output in today's petrol as well as Diesel engines. The most famous small-capacity engines were probably the Porsche 959 and the RX-7 and RX-8 (with the Rotary wankel engine). The 959 produced 450 bhp from 2850 cc and the rotary produced a good amount from the equivalent of 500 cc or something like that.Of course today's CRDI technology is well known and is the reason why most people happily buy diesel cars today.

But IMO the overlooked aspect of this is that by and large when a small engine is used to produce a higher specific output, engine life takes a real beating. I would say a good car needs to last atleast a lakh miles (1.6 lakh km without needing an engine overhaul or seeing a major reduction in engine output.So if you are buying a car like the Honda Jazz, for example you need to keep a watch. Wear and tear on such engines is a lot more in practice.Not sure if modern technology has come up with a solution for this problem too!
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Old 1st February 2010, 16:44   #47
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Quote:
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.
I think its 33 pounds, 1000feet in 1 min and 33,000 pounds, 1foot in 1 min. Anyway, the point being that the same rules/formulas apply to big and small engines, so the gap between the 2 engines can never reduce.

If a 2000cc - 100bhp/ltr engine produces 200bhp@7800, an 5000cc - 100bhp/ltr engine will produce 500bhp.

Shan2nu

Last edited by Shan2nu : 1st February 2010 at 16:50.
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Old 1st February 2010, 21:02   #48
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Pardon my political (in)correctless, but need this example to drive home the point - Are Fat men stronger than lean men?

(I myself am pretty much on the fatter side)
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Old 1st February 2010, 22:06   #49
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Quote:
Originally Posted by hkborah View Post
Pardon my political (in)correctless, but need this example to drive home the point - Are Fat men stronger than lean men?

(I myself am pretty much on the fatter side)
not a good anology. Engines don't build fat over their lifetime. They are born heavier (and stronger). Of course technology matters too.
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Old 1st February 2010, 22:23   #50
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we already have a similar thread

http://www.team-bhp.com/forum/techni...-cc-ratio.html (BHP CC ratio)
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Old 2nd February 2010, 09:35   #51
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AFAIK smaller displacement engines can produce bhp close enough to larger engines, but higher up on the rev band. This results in them lacking grunt in the bottom end.
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Old 2nd February 2010, 10:24   #52
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Quote:
Originally Posted by Gansan View Post
AFAIK smaller displacement engines can produce bhp close enough to larger engines, but higher up on the rev band. This results in them lacking grunt in the bottom end.
This used to be the situation say around 2-5 years back. The K12M produces sufficient low end grunt for its cubic capacity! It all boils down to technology. Now the tech has advanced such that the need to up the cc to up the bhp has reduced considerably from what it used to be say 5 years back. We no longer need V8 and V12 engines to produce good power. The new E250 Merc is a classic case in point. It produces figures close enough to the E350 that it makes the E350 almost redundant.
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Old 2nd February 2010, 10:46   #53
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Quote:
Originally Posted by longhorn View Post
This used to be the situation say around 2-5 years back. The K12M produces sufficient low end grunt for its cubic capacity!
But the TBHP review of the A-Star says the contrary. It comes with this series of engine, does it not? I have not driven the car so far, though.
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Old 2nd February 2010, 15:12   #54
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Quote:
Originally Posted by Gansan View Post
But the TBHP review of the A-Star says the contrary. It comes with this series of engine, does it not? I have not driven the car so far, though.
Neither have I checked out the Tbhp review for AStar nor have I TDed one, but what I have heard is that it is peppy in the city and closes in on the gaps surprisingly well. The main drawback is the roughness attributed to the lack of one cylinder. Not sure if this one lacks low end torque. The point I was trying to make here is that we don't have to depend on high cc engines for better bhp & torque as much as we needed to, say 5 years back. The G13 motor of the Swift is an old school one and lacks low end torque. Not so in the K12M motor of the Ritz, though it is down on cc when compared to the G13.

Last edited by longhorn : 2nd February 2010 at 15:17.
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Old 3rd February 2010, 10:58   #55
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5* for this thread.

Power packed discussion but still we are going haywire with interpretation as we are comparing apples to oranges.

1.2lt i-vtec to 1.5 i-vtec is better comparison than 1.2 TSI to 1.5 i-vtec
and
while we are talking about torque at what RPM we get that usable bandwidth should also be considered 120Nm at 1900RPM vs 103Nm at 4000RPM

Given the same tech, utilization, environment bigger is better for power and delivery. Smaller is better for FE.

And to add that shape (V vs Inline vs Boxter) also plays a lot in the equation. Reliability of a stressed engine will fall, F1 engines are not meant to last 1mn kms and thus these are more stressed.

I say size is not redundant depends on the usage.
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Old 3rd February 2010, 11:25   #56
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On a lighter note, here's somebody who decided to answer the question once and for all!
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Old 3rd February 2010, 17:25   #57
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IMHO the new small engines producing higher BHPs are just more efficient than the older ones due to the technology involved. The same technology applied to a bigger engine will surely do much better in terms of power delivery. But hey FE is name of the game in the market. So companies like there high performing smaller engines which give out a good FE too.
But i guess it will take a beating when it comes to engine life.
The older bigger cars were made to last forever and i dont think the new ones will stand a chance when it comes to this aspect.
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Old 3rd February 2010, 21:51   #58
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Quote:
Originally Posted by tj123 View Post
Theoretically speaking if all parameters are same a bigger engine with more displacement will produce more torque.
Torque is flywheel mass dependent as also the final drive ratio.

Quote:
Originally Posted by Mi10 View Post
There is something called "Compression ratio"

A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency

However, the higher octane fuel is needed - else it would result in engine knocking
Higher compression ratio engines wear out faster than low compression ratio engines.

Quote:
Originally Posted by Psycho View Post
However you will note that higher displacement engines are typically designed for high torque and low rpm leading to longer engine life vs. smaller engines with forced induction used to be prone to failure (note I said used to), todays technologies are allowing the newer engines to be built better rather than just a turbo / supercharger being added hence ensuring better engine life.
The smaller engines CANNOT match the engine life of the larger low rpm engines.


Quote:
Originally Posted by Shan2nu View Post
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).
The 4 ltr engine will be slower than the 2 ltr one!

Quote:
Originally Posted by Shan2nu View Post
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.
Agreed!

Quote:
Originally Posted by Shan2nu View Post
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
A +10 to that, add to it the cost of raw material and production

IMHO: Theres no replacement for displacement - Old school thoughts but well IC engines are old too!
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Old 4th February 2010, 21:06   #59
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Quote:
Torque is flywheel mass dependent as also the final drive ratio.
I agree with the final drive ratio part. Any increase in FD ratio will improve torque at the wheels (not at the crank).

But, a flywheel does not increase torque, it only stores rotational energy which prevents the car from losing momentum quickly, which makes the driver think the torque has improved.

How a lightweight flywheel works

Quote:
The 4 ltr engine will be slower than the 2 ltr one!
Not if both engines are in the same state of tune.

2ltr engine - 200bhp - 200nm - 10kg flywheel
4ltr engine - 400bhp - 400nm - 20kg flywheel.

The 4ltr engine might have twice the rotaional mass of the 2ltr engine but it also has twice the bhp and torque output. So both engines will be equally revv happy.

Shan2nu
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