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Old 12th July 2010, 15:58   #136
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Default Power band and Rev range....

I own a Honda City ZX VTEC+ 2008 model. I find that although it runs without effort at low speeds in the city, its highway performance leaves a lot to be desired. Maybe it is my driving style.

What I would like to know is how does one "drive in the power band", how do i rev the engine to take the RPM to its 3000 - 5000 RPM power band....Once i am in the 4th or 5th gear, how do i keep it in the power band?

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Old 13th July 2010, 09:30   #137
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Quote:
Originally Posted by venkateshkm View Post
Once i am in the 4th or 5th gear, how do i keep it in the power band?
The topmost gears are intended for cruising at one speed, while the 5th is generally very tall for stress free fuel-efficient touring. The engine is lazily ticking over at a mere 1,500 - 2,000 rpms. To get into the powerband, you will need to drop the gears down to 3rd (or even 2nd if at a lower speed, say 60 kph) in a petrol car.
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Old 7th August 2010, 23:53   #138
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Originally Posted by Shan2nu View Post

You can't make a 2ltr NA engine produce 200bhp@6000rpm but you can make a 2ltr FI engine do it.

A Veyron does 123bhp/ltr@6000rpm, try and find a NA engine which can do this, you wont.

Shan2nu
I have to disagree with this very strongly. A lot of what you have said in your previous posts is very good information but as far as 2ltr N/A's not being able to produce 200hp at around 6k, thats very wrong! I have lost count of the amount of N/A engines i've tuned to around those figures over the years!

There has been a lot of mention of the various aspects that are used for deriving figures and some of the theory around it but what suprises me is that there has been no mention of volumetric efficiency.

The point of the highest VE of a N/A engine is were you will find peak torque.

F1 engines can produce VE figures into and over the 120% figures but only over very small RPM ranges. Find the point of peak VE and thats your peak torque figure in a N/A engine!



Quote:
Originally Posted by ukamath View Post
Ok...This might be a dumb question to all the intelligent folks out there, but still taking the courage to ask.

With so many new launches happening and everyone showing off different specs of engines, I am majorly confused with the the terms BHP and torque - PS and NM respectively.
  1. In some cars the bhp is lower, but have a higher torque (mostly diesels I guess) and the other way around. Why is it so?
  2. If a car has higher bhp, does it necessarily mean more power to the wheels?
  3. How does each of these - BHP and TORQUE, affect my driving in the city (low to mid range pulling) and the highways (top end pull)
Coming to the cylinder terminologies - Is a 4 cylinder necessarily better than a 3? Will a modern 3 cylinder (POLO / K-Series...) have the same sweet exhaust note and be more smooth than a 4 cylinder?

Thanks!
I'm unsure of how 3 cylinder technology is progressing out in India but certainly the 3 cylinder engines we have in the UK may well be fuel efficient but they sound awful! They are so unbalanced they always sound like a four cylinder thats about to die!
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Old 8th August 2010, 04:24   #139
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Originally Posted by ukamath View Post
Coming to the cylinder terminologies - Is a 4 cylinder necessarily better than a 3? Will a modern 3 cylinder (POLO / K-Series...) have the same sweet exhaust note and be more smooth than a 4 cylinder?

Thanks!
Three cylinder engines are high on FE for a given 'cc'. I think thats the only major benefit of those over a four cylinder engine.
Other than that, the major problem of a three cylinder engine is 'balancing'. These three/odd cylinder engines are very complicated to balance and hence they are not so refined as the four cylinder ones. That's why a 4 cylinder NVH is better than a 3 cylinder one.
I bet you can see a notable difference in NVH's of Polo 1.2 & 1.6.
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Old 9th August 2010, 18:03   #140
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Dyno sheet of a 200bhp N/A engine



And a sheet for a 2ltr running big boost! 800 bhp
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Old 9th August 2010, 18:55   #141
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Default Check this article out

Hi,
Found quite a nice write up on this very complex stuff.
Please check this link Horsepower and Torque: A Practical Explanation

Please accept my apologies, if someone has already posted the above link.

But one very interesting thing below:- (No doubt, got it from a site :-))
Design-wise the two requirements above are at two ends of the spectrum. The engine designs does not allow both at the same time - for instance while Torquish engines need small valves, non-torquish engine needs a bigger valve. While trucks with smaller valves run out of breath after a certain rpm, the non-torquish bike engines runs swifter reaching very high rpms of upto 14000.

Honda’s answer to above situation is vvt – variable valve technology. Mitsubishi is MIVEC – “Mitsubishi Innovative Valve-Timing Electronic Control system”. As an example : Mitsubishi’s MIVEC sedan Evo-X FQ makes 410 bhp and 510 Torque out of a tiny 2.0 litre petrol engine !!


Best Regards

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Old 24th March 2011, 10:23   #142
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Default Re: Torque vs BHP?

Why is it difficult to drive a car with low end torque in the city ?
Are they made only for the highways ?
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Old 24th March 2011, 11:06   #143
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Default Re: Torque vs BHP?

^^You mean 'without', right?

Because (more often than not) you find yourself in too high a gear and you have to downshift.

But it's possible to drive well in the city even in a car with suboptimal torque, it's just a little more taxing.

And usually, small engines are designed to deliver fuel efficiency first, so torque and power become secondary, hygiene-led considerations. So, no, they're not meant for highways either.

I prefer cars with peak torque higher up in the rev range. They're easier to keep on the boil.

In my mind the optimal space between the peak torque and peak power curve is the duration of a gearshift. This is why you will notice racing drivers 'blip' the throttle....
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Old 24th March 2011, 11:36   #144
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Default Re: Torque vs BHP?

Quote:
Originally Posted by karty_83 View Post
Why is it difficult to drive a car with low end torque in the city ?
Are they made only for the highways ?
I suppose you mean a low (quantum of), low-end torque (i.e. low rpm torque). Low-end torque is needed to accelerate a stationary 1500 kg. vehicle to 40 km/h.

City driving is characterized by an endless series of staccato starts and stops, as one moves from signal to signal, negotiating around slow moving autorickshaws, microtrucks (growing rash of underpowered Tata Aces impeding all traffic) two-wheelers who ride blind to other road users' stress levels and and heavy commercial vehicles.
And this needs to be done repeatedly in city driving.

On the other hand on the Mumbai-Pune expressway, for great stretches of road, one cruises steadily in 5th gear at 110 km/h, with the rpm needle hovering around 2900 rpm. The heavy hurtling vehicle requires less torque to maintain momentum (mass x speed).
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Old 24th March 2011, 14:11   #145
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Default Re: Torque vs BHP?

Quote:
Originally Posted by cranky View Post
^^You mean 'without', right?
Oh Yes i meant without.

Quote:
Originally Posted by Ram View Post
I suppose you mean a low (quantum of), low-end torque (i.e. low rpm torque). Low-end torque is needed to accelerate a stationary 1500 kg. vehicle to 40 km/h.
A car like Fiesta diesel has torque peaking at lower rpm's while others like Swift petrol have torque peaking at higher rpm's. This leads to constant gear shifting in city conditions and is very taxing.

So, was wondering if cars like the Swift (p) or the Fabia (1.6) or the Jazz (1.2) are made just for the highways as they require constant down shifting in city driving conditions.
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Old 24th March 2011, 14:36   #146
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Default Re: Torque vs BHP?

Quote:
Why is it difficult to drive a car with low end torque in the city ?
Are they made only for the highways ?
In most cases, it's not the car but the choice of gear by the driver, that causes this problem.

A person who is used to driving a turbo diesel, might not downshift to a suitable gear on a high revving petrol, making the engine bog down as the vehicle speed drops.

Once you get accustomed to the characteristics of a high revving engine, you wont find it difficult.

Shan2nu
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Old 24th March 2011, 16:27   #147
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Default Re: Torque vs BHP?

Quote:
Originally Posted by karty_83 View Post
So, was wondering if cars like the Swift (p) or the Fabia (1.6) or the Jazz (1.2) are made just for the highways as they require constant down shifting in city driving conditions.
Actually, these are cars made mainly for the city. Well, manufacturers must have loved to give good low end drivability to these cars, but then, the engine/price/package are most balanced this way. So, one will have to manage with lower gears.
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Old 24th March 2011, 20:15   #148
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Default Re: Torque vs BHP?

Quote:
Originally Posted by cranky View Post
This is why you will notice racing drivers 'blip' the throttle....
To match speeds.

Quote:
Originally Posted by Ram View Post
The heavy hurtling vehicle requires less torque to maintain momentum (mass x speed).
Don't get it.

Regards
Sutripta
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Old 24th March 2011, 22:33   #149
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Default Re: Torque vs BHP?

Cars = diesels = torque. Much so because you have to commute and drive on the street.

Yes, its fun (much more fun than a diesel) to pilot a petrol Car, but those moments are very few and far in between.

Give me a Motorcycle which redlines at 19,000 and is a dud (relatively) below 10K and I won't complain.
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Old 25th March 2011, 10:07   #150
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Default Re: Torque vs BHP?

Don't get this constant crib about less low-end torque.

Things are simple to manage. Use 3rd gear (instead of trying for 5th every time) - there is a reason why you are provided with 5 different gears. Utilize them.
I don't know why but everyone in India has a tendency to up-shift at the earliest.
This is what causes you to downshift again when the speed goes low.
(And label the car as difficult to drive in city)

Probably ppl don't like the sound of engine revving (even at 3000 RPM) - or probably they are used to vehicles that redline at 3000 RPM?
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