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Old 28th October 2011, 12:56   #76
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Default Re: Petrol vs diesel torque characteristics & driving pattern

A few observations:

1. For an urban dweller for whom 90% (or more) of the driving is in the city, I believe the petrol makes more sense. I have heard a lot of people mention the very good low end torque of small diesels. However, from my experience of drving small diesels, the torque that one talks about comes in only after 2000 RPM (plus or minus a couple of hundred revs). In normal city conditions, it is actually quite difficult to hold the revs above that level for any sustained period of time. Therefore, for city driving, a petrol motor with linear power delivery feels much more comfortable to me, even though in a petrol peak power comes in much later. If I think about my driving, peak power is rarely used/reached (if at all) by most of us on an average office drive, or weekend trip to the restaurant. On a highway drivie, possibly yes.

Highway driving of course is another ball game, since the diesel engine can be largely kept in the power band, thus utilising the spread of torque resulting in good cruising ability etc.

2. For a monthly commuting of 800-1000 kms (a common figure amongst a lot of us), the break even point comes after several years. This of course is not true for persons with high monthly running. Even after that, one would save Rs.2-3 k on fuel per month (i.e. after the break even period gets over). From my understanding, this figure too is offset to some extent by higher maintenance costs of diesels as the kms get clocked. For a typical five year ownership, financial gains probably start after the fourth year or so. Too long away to forsake the pleasure of an enthusiastic petrol engine.

3. For petrol enthusiasts, nothing beats the silky feel of a smooth engine coupled with a snappy gearbox and a tight chassis. This again is a purely subjective opinion.

However, diesels would give that feel good factor economy wise, when a tankful costs way lesser than in petrol siblings. Its pretty easy to forget that one has already paid a lakh + extra in buying the diesel variant in the first place.

At the end of the day, to each his own I suppose. The debate would go on for ages.

Last edited by arindambasu13 : 28th October 2011 at 12:59.
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Old 28th October 2011, 14:48   #77
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Default Re: Petol vs diesel torque characteristics & driving pattern

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Originally Posted by oxyzen View Post
Power band in this diesel is 3000-5000. For petrol it is 5500-6500. I think powerband of diesel is wider. Please understand you need to keep the engine in the powerband to extract the maximum performance. For a petrol it is too high & too narrow.
Hi,
How is the powerband arrived at?

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Old 28th October 2011, 15:05   #78
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Default Re: Petrol vs diesel torque characteristics & driving pattern

My experience with Palio 1.9 D has been that one has to shift constantly during an acceleration run as the engine runs out of breath as soon as it hits 4000 RPM. While on most petrol engines one can hold on to a gear during acceleration moves.

I feel that highway maneuvers (upshift, downshift etc) are specific engine/vehicle dependent, difficult to generalize between a petrol and a diesel.
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Old 28th October 2011, 15:39   #79
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Default Re: Petrol vs diesel torque characteristics & driving pattern

No issues with the graphs and the inferences. However what if we replace the N.A. petrol engine with a similar capacity turbo petrol engine? Can anyone post similar comparison charts for let's say a 1.4 L turbo petrol vs 1.4 L crdi or a 1.8L/2.0L turbo petrol vs a 1.8/2.0 L crdi? It would be interesting to see if the turbo petrols can match the diesels in the mid range, which is where the diesels crush the N.A. petrols.
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Old 28th October 2011, 19:37   #80
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Default Re: Petol vs diesel torque characteristics & driving pattern

Quote:
Originally Posted by MileCruncher View Post
@Oxyzen: The things you are trying to state have already been covered/discussed on an existing thread http://www.team-bhp.com/forum/techni...l-engines.html (Do Diesel engines generate more Torque than Petrol engines?)
Cheers
This thread is a bit different. Here the point is to find the perfect driving pattern diesels & petrols. It for studying the torque characteristics and then understanding with the practical scenario.


Quote:
Originally Posted by Astleviz View Post
Can anyone post similar comparison charts for let's say a 1.4 L turbo petrol vs 1.4 L crdi or a 1.8L/2.0L turbo petrol vs a 1.8/2.0 L crdi?
Sorry I dont have any turbo petrol engines right now. I bet it will be interesting.

Quote:
Originally Posted by Sutripta View Post
Hi,
How is the powerband arrived at?
Sutripta
I knew you would ask.
Infact I see the power band as the RPM range where I can get approximately 90% of my max power. For a diesel starting from 3000 RPM and till 5000 RPM I can enjoy max power. (See power graph & not torque graph)
In the petrol power graph, 5500 to 6500 is where I get max power. So the Petrol has narrow power band.
I admit the torque band of petrol in much much wider.

I know what I am saying is against the general convention. But in a race on track where you want to extract max performance out of the engine, you have to be in 5500-6500 RPM in a petrol by being in the proper gear. In a diesel it is 3000-5000.

Last edited by oxyzen : 28th October 2011 at 19:55.
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Old 28th October 2011, 19:52   #81
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Default Re: Petrol vs diesel torque characteristics & driving pattern

Now here comes the most interesting part.

Acceleration vs speed graph.

I have used torque/tonne. Then using the gear ratios or (more specifically V1000 for both these cars) I have calculated the acceleration in each gears and plotted them against speed.

I have not taken into account the drop in acceleration due to drag co-efficient & other factors. For that I need the road load values which I will try to do sometime in future. The acceleration values are relative.

Do Diesel engines generate more Torque than Petrol engines?-acc.jpg

Note: the petrol has better power to weight ratio.

Last edited by oxyzen : 28th October 2011 at 19:53.
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Old 28th October 2011, 19:59   #82
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Default Re: Petrol vs diesel torque characteristics & driving pattern

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Originally Posted by oxyzen View Post
Now here comes the most interesting part.

Acceleration vs speed graph.
If I assume that the five set of curves is for gears 1-5, then this plot tells me that acceleration is better for the blue car (petrol) as it always beats the red (diesel) on the X axis which is speed (?).
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Old 28th October 2011, 20:25   #83
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Default Re: Petrol vs diesel torque characteristics & driving pattern

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Originally Posted by dot View Post
If I assume that the five set of curves is for gears 1-5, then this plot tells me that acceleration is better for the blue car (petrol) as it always beats the red (diesel) on the X axis which is speed (?).
Yup they are for gears 1-5.
Blue is for petrol & red for diesel.
X axis is speed.

Yes after 60 Kmph petrol beats the diesel hands down. And it is not unusual. Because petrol not only produces more power but is also lighter in comparison.
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Old 28th October 2011, 20:34   #84
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Default Re: Petrol vs diesel torque characteristics & driving pattern

Quote:
Originally Posted by oxyzen View Post

Yes after 60 Kmph petrol beats the diesel hands down. And it is not unusual. Because petrol not only produces more power but is also lighter in comparison.
Why only 60 kmph, as soon as peak torque is over, the red (Diesel) car will have to shift to next gear, thus taking up time.

The way I see the plots, the red has to shift gears three times when the blue have to shift once.

Last edited by dot : 28th October 2011 at 20:36.
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Old 28th October 2011, 20:50   #85
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Default Re: Petrol vs diesel torque characteristics & driving pattern

No you got it wrong mate.
The red will shift when one red line (1st gear) crosses the other (2nd gear).
Take a speed of 50kmph for example. The diesel will be in 2nd gear and it will out accelerate the petrol (which is also in 2nd gear).
Take a speed of 80 kmph. The petrol will be in 2nd gear and it will out accelerate the diesel (which has shifted to 3rd).
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Old 28th October 2011, 22:28   #86
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Default Re: Petrol vs diesel torque characteristics & driving pattern

Quote:
Originally Posted by oxyzen View Post
No you got it wrong mate.
The red will shift when one red line (1st gear) crosses the other (2nd gear).
Take a speed of 50kmph for example. The diesel will be in 2nd gear and it will out accelerate the petrol (which is also in 2nd gear).
Take a speed of 80 kmph. The petrol will be in 2nd gear and it will out accelerate the diesel (which has shifted to 3rd).
Wont the petrol car be left behind by 6-7 car lengths by the time you hit 80? Simply due to better torque from diesel.
Wont the diesel mill send more torque to wheels even in 3rd gear as compared petrol in 2nd gear ,for most of regular cars.
May be not,but it certainly wont be too little even in 3rd.
By the way which card does 80 in 2nd and is still willing to go further?
I dont know what for are you plotting graphs and on what gearbox data.
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Old 28th October 2011, 23:42   #87
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Default Re: Petrol vs diesel torque characteristics & driving pattern

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Originally Posted by dustom_99 View Post
Wont the petrol car be left behind by 6-7 car lengths by the time you hit 80? Simply due to better torque from diesel.
cant really say.
As per graph diesel will be faster in the range of (10-35)kmph. (both in 1st gear)
Petrol will be faster in the range (35-45). Petrol in 1st diesel in 2nd.
Again diesel will be faster in the range of (45-60)kmph. (both in 2nd gear gear)
Petrol will be faster in the range (60-85). Petrol in 2nd diesel in 3rd.

Now this is something that I could find out using this graph.

Quote:
Originally Posted by dustom_99 View Post
Wont the diesel mill send more torque to wheels even in 3rd gear as compared petrol in 2nd gear ,for most of regular cars.
May be not,but it certainly wont be too little even in 3rd.
Not with the gear ratios of these cars. Also this petrol is slightly more powerful.

Quote:
Originally Posted by dustom_99 View Post
By the way which card does 80 in 2nd and is still willing to go further?
Almost all present day petrols with 1.2L engines and up. Leave aside the hondas. They are good for even 100.

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Originally Posted by dustom_99 View Post
I dont know what for are you plotting graphs and on what gearbox data.
It is on V1000. The speed of the car at 1000 engine RPM. It takes into account gear ratios, final drive ratios, wheel size and all.
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Old 28th October 2011, 23:47   #88
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Default Re: Petol vs diesel torque characteristics & driving pattern

Quote:
Originally Posted by oxyzen View Post
I knew you would ask.
Infact I see the power band as the RPM range where I can get approximately 90% of my max power. For a diesel starting from 3000 RPM and till 5000 RPM I can enjoy max power. (See power graph & not torque graph)
In the petrol power graph, 5500 to 6500 is where I get max power. So the Petrol has narrow power band.
Don't agree with your interpretation.
Quote:
I know what I am saying is against the general convention.
Agree. There is a basis for the convention.

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Old 29th October 2011, 01:06   #89
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Default Re: Petrol vs diesel torque characteristics & driving pattern

Quote:
Originally Posted by oxyzen View Post
cant really say.
As per graph diesel will be faster in the range of (10-35)kmph. (both in 1st gear)
Petrol will be faster in the range (35-45). Petrol in 1st diesel in 2nd.
Again diesel will be faster in the range of (45-60)kmph. (both in 2nd gear gear)
Petrol will be faster in the range (60-85). Petrol in 2nd diesel in 3rd.

Now this is something that I could find out using this graph.


Not with the gear ratios of these cars. Also this petrol is slightly more powerful.


Almost all present day petrols with 1.2L engines and up. Leave aside the hondas. They are good for even 100.


It is on V1000. The speed of the car at 1000 engine RPM. It takes into account gear ratios, final drive ratios, wheel size and all.


AS PER GRAPH MY FRIEND,AS PER GRAPH! Which hapns to be your graph,without any public data.
Weird privacy policy that stops you from disclosing data which is already available all over net (gear ratios,tyre size,engine specs).
Even as per your graph,petrol wil only be doing catching up ,as it would be left behind right at the start' close the gap a little bit (just a lil bit) in the zone 35-45,and then 65-80.
I hope you are not expecting the petrol to find some magic wand of torque in these zones that it would suddenly overhaul all the gap.
When this guy finally shifts to next gear,gap which never got compleatly ouerhauled will start to increase further,because when in same gear diesel would have upper hand.
Now at the next gear shift the petrolhead has even bigger gap to fathom.
Petrol will finally win the top speed battle,owing to its higher bhp and it is certainly going to take quite a streach .

I dont know where did you get data from,and I agree some cars will make it to 80 may be even 85,but beyond 70 it is quite a labour even for a petrol mill(of usual cars),and they take lot longer to get to 80 in 2nd as compared to the situation where you pass the sweet spot just enough that the next gear will fall rite onto the sweet spot or just below it.
If you wana get to 80 just for heck of getting there,then its different.
And I could not understand the policy behind plotin acc v1000?whats that for?
100 in 2nd gear? Must be on 19 or 20 inch rubber, stock tyre size would take them deep into 9000rpm ,i think thats not stock or is it?
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Old 29th October 2011, 06:35   #90
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Default Re: Petrol vs diesel torque characteristics & driving pattern

Quote:
Originally Posted by oxyzen View Post
Take a speed of 50kmph for example. The diesel will be in 2nd gear and it will out accelerate the petrol (which is also in 2nd gear).
Looking at these plots, if I were the driver of the red car and to take advantage of the peak torque and acceleration, I would be in 3rd gear by the time speed reached 50kmph. In the blue car I would be in 2nd and will continue in that gear till speed reaches 80 odd. Thats what I meant.

Quote:
Originally Posted by dustom_99 View Post
100 in 2nd gear? Must be on 19 or 20 inch rubber, stock tyre size would take them deep into 9000rpm ,i think thats not stock or is it?
Why not possible friend? My car goes to 100 in 2nd gear in about 10 sec and it is all stock.
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