Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 8th May 2011, 22:59   #166
BHPian
 
Born2Slow's Avatar
 
Join Date: May 2007
Location: Bnagalore/Cochin
Posts: 86
Thanked: 42 Times
Default Re: Torque vs BHP?

The thing that annoys me is that people compare torque figures of a diesel and petrol. But what one should also consider is that diesels usually produce their max power at much less rpm than an equivalent petrol engine so most of the higher torque is offset by taller gearing by the time it reaches the wheel. So its very unfair on the petrol engines.
Born2Slow is offline   Reply With Quote
Old 9th May 2011, 02:40   #167
Senior - BHPian
 
Join Date: Dec 2010
Location: Ghaziabad/Hyderabad/Mysore
Posts: 1,416
Thanked: 313 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by Born2Slow View Post
The thing that annoys me is that people compare torque figures of a diesel and petrol. But what one should also consider is that diesels usually produce their max power at much less rpm than an equivalent petrol engine so most of the higher torque is offset by taller gearing by the time it reaches the wheel. So its very unfair on the petrol engines.
I don't know why it should annoy you. At the top end, diesels do not go to the same rpm levels as petrols (and this get beaten up on peak power). At the lower end, there is serious turbo-lag (=no torque, no power). This is well known and all serious performance guys go for petrols for these two reasons.

Coming to comparisons of torque, you would be right if the gear ratios of petorl/diesel were very different. However that is not the case (you can check on Autocar India profiles and even get the information on team bhp) - several cars share the same transmission while those who do have similar gear ratios for petrol/diesel do not have wildly different ones.

End result - the difference in torque does show up at the wheels too.

However this may actually be a bigger disadvantage for diesel - on Figo for example, both the petrol and diesel engines max out at about 70bhp. However the petrol maxes out at a higher rpm (and hence potentially higher vehicle speed) than the diesel. Given that more power is needed at higher speeds (air drag is the biggest force at high speeds) petrols provide the power right when needed, while diesel doesn't.

Even climbing inclines is not a black and white area - if you have some speed on your wheels diesel will win hands down. BUT if you happen to stop, a diesel requires serious clutch slipping compared to a petrol - there simply is no torque at low rpm numbers.

The only area where the extra torque comes handy is in overtaking at speeds of 50-70, at these speeds in high gears diesel can provide better acceleration. On the other hand if you are willing to shift down even a petrol engine will provide pretty good (even better) acceleration.


Overall, the guys who buy diesels don't buy it because of performance reasons - petrols usually give much better overall performance for any use - the reason is economy.

Last edited by vina : 9th May 2011 at 02:46.
vina is offline   Reply With Quote
Old 9th May 2011, 10:13   #168
BHPian
 
DWind's Avatar
 
Join Date: Apr 2007
Location: Singara Chennai
Posts: 775
Thanked: 168 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by vina View Post
Even climbing inclines is not a black and white area - if you have some speed on your wheels diesel will win hands down. BUT if you happen to stop, a diesel requires serious clutch slipping compared to a petrol - there simply is no torque at low rpm numbers.
Are you sure? I always felt that better low end torque in Diesels (compared to its petrol siblings) would make it climb better with no clutch slipping required.
DWind is online now   Reply With Quote
Old 9th May 2011, 11:34   #169
BHPian
 
Born2Slow's Avatar
 
Join Date: May 2007
Location: Bnagalore/Cochin
Posts: 86
Thanked: 42 Times
Default Re: Torque vs BHP?

Yes Vina more or less what I meant. The example you gave is quite good for proving my point. Lets take the Figo

Diesel Figo
  • 1.4 Liter DuraTorq CRDI Diesel Engine
  • Max Power 68 BHP @4000 RPM
  • Max Torque 160 Nm @ 2000 RPM
Petrol Figo
  • 1.2 Liter DuraTec MPFI Petrol Engine
  • Max Power 70 BHP @6250 RPM
  • Max Torque 104 Nm @ 4000 RPM
Vina it is very unlikely the two cars run similar gearing because there is lot of difference between their max power RPMs. Do you have the kmph/1000 rpm in each gear for the two cars as i could not find it.Even if the two cars run same gear box for whatever reason they may chose to, the final drive ratio has to be different.
Born2Slow is offline   Reply With Quote
Old 9th May 2011, 11:37   #170
BHPian
 
Born2Slow's Avatar
 
Join Date: May 2007
Location: Bnagalore/Cochin
Posts: 86
Thanked: 42 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by DWind View Post
Are you sure? I always felt that better low end torque in Diesels (compared to its petrol siblings) would make it climb better with no clutch slipping required.
May be due to turbo lag.
Born2Slow is offline   Reply With Quote
Old 9th May 2011, 12:19   #171
BHPian
 
teknophobia's Avatar
 
Join Date: Mar 2008
Location: Ahmedabad
Posts: 319
Thanked: 22 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by vina View Post
I don't know why it should annoy you. At the top end, diesels do not go to the same rpm levels as petrols (and this get beaten up on peak power). At the lower end, there is serious turbo-lag (=no torque, no power). This is well known and all serious performance guys go for petrols for these two reasons.

... However this may actually be a bigger disadvantage for diesel - on Figo for example, both the petrol and diesel engines max out at about 70bhp. However the petrol maxes out at a higher rpm (and hence potentially higher vehicle speed) than the diesel. Given that more power is needed at higher speeds (air drag is the biggest force at high speeds) petrols provide the power right when needed, while diesel doesn't....

...The only area where the extra torque comes handy is in overtaking at speeds of 50-70, at these speeds in high gears diesel can provide better acceleration. On the other hand if you are willing to shift down even a petrol engine will provide pretty good (even better) acceleration.


Overall, the guys who buy diesels don't buy it because of performance reasons - petrols usually give much better overall performance for any use - the reason is economy.

It doesn't seem like you have driven the two cars or diesel versions of similar vehicles. I can assure you that diesels rarely require you to slip the clutch when climbing inclines at low speeds. It is in fact petrol vehicles which require you to do so as usable torque is nonexistent at lower rpm levels. Try going up a steep incline at low speeds with the two cars and let us know which one required you to slip the clutch.

Also, I would suggest you take a look at the torque curves for the two cars and not just when peak torque is generated. Diesels are noisy, accelerate and decelerate slower and require you to change gears often, but torque is not something they lack.
teknophobia is offline   Reply With Quote
Old 9th May 2011, 12:27   #172
Senior - BHPian
 
mayankk's Avatar
 
Join Date: Apr 2010
Location: New Delhi
Posts: 4,115
Thanked: 3,489 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by teknophobia View Post
Also, I would suggest you take a look at the torque curves for the two cars and not just when peak torque is generated. Diesels are noisy, accelerate and decelerate slower and require you to change gears often, but torque is not something they lack.
+1 to that.
which is the reason you'll find all industrial/heavy machinery engines running diesel units.
mayankk is online now   Reply With Quote
Old 9th May 2011, 13:16   #173
Senior - BHPian
 
Join Date: Dec 2010
Location: Ghaziabad/Hyderabad/Mysore
Posts: 1,416
Thanked: 313 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by teknophobia View Post
It doesn't seem like you have driven the two cars or diesel versions of similar vehicles. I can assure you that diesels rarely require you to slip the clutch when climbing inclines at low speeds. It is in fact petrol vehicles which require you to do so as usable torque is nonexistent at lower rpm levels. Try going up a steep incline at low speeds with the two cars and let us know which one required you to slip the clutch.

Also, I would suggest you take a look at the torque curves for the two cars and not just when peak torque is generated. Diesels are noisy, accelerate and decelerate slower and require you to change gears often, but torque is not something they lack.
Hi

what I meant (and I thought clearly mentioned) was that once the vehicle is moving diesel wins hands down. However if you are starting from zero speed, diesel will need more clutch slipping initially - there simply is no torque at very low speeds.

I myself learned to drive on an old WagonR at Maruti driving school, and now I'm driving a Figo diesel. The diesel has way more power than the WagonR's petrol but if I stall on even a moderate incline, the difference is very obvious. WagonR would start moving much more easily than this one does.

Once the car has attained even 10kmph however, the story is quite different.
vina is offline   Reply With Quote
Old 9th May 2011, 13:38   #174
Senior - BHPian
 
Join Date: Dec 2010
Location: Ghaziabad/Hyderabad/Mysore
Posts: 1,416
Thanked: 313 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by Born2Slow View Post
Yes Vina more or less what I meant. The example you gave is quite good for proving my point. Lets take the Figo

Diesel Figo
  • 1.4 Liter DuraTorq CRDI Diesel Engine
  • Max Power 68 BHP @4000 RPM
  • Max Torque 160 Nm @ 2000 RPM
Petrol Figo
  • 1.2 Liter DuraTec MPFI Petrol Engine
  • Max Power 70 BHP @6250 RPM
  • Max Torque 104 Nm @ 4000 RPM
Vina it is very unlikely the two cars run similar gearing because there is lot of difference between their max power RPMs. Do you have the kmph/1000 rpm in each gear for the two cars as i could not find it.Even if the two cars run same gear box for whatever reason they may chose to, the final drive ratio has to be different.
this is for Figo (source: http://www.autocarindia.com/roadtest/ford-figo):

1st3.58/7.00, 3.58/7.792nd
1.93/12.99, 1.93/14.45 3rd
1.28/19.58, 1.28/21.79 4th
0.95/26.39, 0.95/29.365th
0.76/32.99, 0.76/36.70Final drive ratio
4.25:1, 3.82:1
If you see, the overall difference between the two gear ratios in about 20%, while the difference in torques is 40%. This means diesel will still retain 20% more torque on the wheels - though at stall speeds there will be almost no torque in diesel whereas petrol will still have some.

By the way, other cars have even less difference than the above for example Maruti swift (data taken from IndiaMART: Page not found

Gear ratios

Gear Ratio 1st 3.545 3.545 Gear Ratio 2nd 1.904 1.904 Gear Ratio 3rd 1.280 1.233 Gear Ratio 4th 0.966 0.911 Gear Ratio 5th 0.757 0.725 Reverse 3.272 3.250
As you can see there is very little difference between petrol and diesel versions on the swift - diesel swift will feel very have very high torque on the wheels compared to petrol swift.

It'll take you some work, but gear ratio of most cars that give both diesel/petrol versions can be found on the internet and/or on team bhp. You'll find that petrol vs. diesel gearing has minimal differences (in fact Figo is more of an exception).
vina is offline   Reply With Quote
Old 9th May 2011, 14:42   #175
BHPian
 
teknophobia's Avatar
 
Join Date: Mar 2008
Location: Ahmedabad
Posts: 319
Thanked: 22 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by vina View Post
Hi

what I meant (and I thought clearly mentioned) was that once the vehicle is moving diesel wins hands down. However if you are starting from zero speed, diesel will need more clutch slipping initially - there simply is no torque at very low speeds.

I myself learned to drive on an old WagonR at Maruti driving school, and now I'm driving a Figo diesel. The diesel has way more power than the WagonR's petrol but if I stall on even a moderate incline, the difference is very obvious. WagonR would start moving much more easily than this one does.

Once the car has attained even 10kmph however, the story is quite different.
If you're trying to start a car with a manual transmission on a moderate incline, any car will require clutch slippage. Most of these driving schools have their cars tuned so that the car doesn't stall easily. Unlike petrols, diesels are very difficult to stall and so if you're stalling a diesel car on a regular basis, there is something seriously wrong with your driving style.
teknophobia is offline   Reply With Quote
Old 9th May 2011, 15:23   #176
BHPian
 
ajman28's Avatar
 
Join Date: May 2010
Location: Chennai
Posts: 277
Thanked: 22 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by vina View Post
Hi

what I meant (and I thought clearly mentioned) was that once the vehicle is moving diesel wins hands down. However if you are starting from zero speed, diesel will need more clutch slipping initially - there simply is no torque at very low speeds.

I myself learned to drive on an old WagonR at Maruti driving school, and now I'm driving a Figo diesel. The diesel has way more power than the WagonR's petrol but if I stall on even a moderate incline, the difference is very obvious. WagonR would start moving much more easily than this one does.

Once the car has attained even 10kmph however, the story is quite different.
I too have my doubts on this case.

From a standstill, both diesel and petrol require clutch slipping. Even if it's on an inclination, the petrol will require more slipping to attain 4000 odd rpm for getting the vehicle to move while a diesel engine will require only about 2000 odd rpm (considering that both are average hatchbacks we find). In such a case, how would you say that a petrol engine is more powerful at a lower rpm?

Last edited by ajman28 : 9th May 2011 at 15:26.
ajman28 is offline   Reply With Quote
Old 9th May 2011, 16:26   #177
Senior - BHPian
 
Join Date: Dec 2010
Location: Ghaziabad/Hyderabad/Mysore
Posts: 1,416
Thanked: 313 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by teknophobia View Post
If you're trying to start a car with a manual transmission on a moderate incline, any car will require clutch slippage. Most of these driving schools have their cars tuned so that the car doesn't stall easily. Unlike petrols, diesels are very difficult to stall and so if you're stalling a diesel car on a regular basis, there is something seriously wrong with your driving style.

you are spot on when it comes to my driving style. However one week of practice and I'm not stalling much (except when some Hyderabadi Hero Hiralal cuts in front of me and I have to brake suddenly - sometimes at low speeds I do stall).

You may be right about the driving school vehicle and clutch slipping was needed on that one too to some extent (Maruti guys call it "biting point" method) on inclines. However I do find that my Figo takes more effort than those WagonRs did on moderate inclines to start from a complete stop.
vina is offline   Reply With Quote
Old 9th May 2011, 16:37   #178
Senior - BHPian
 
Join Date: Dec 2010
Location: Ghaziabad/Hyderabad/Mysore
Posts: 1,416
Thanked: 313 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by ajman28 View Post
I too have my doubts on this case.

From a standstill, both diesel and petrol require clutch slipping. Even if it's on an inclination, the petrol will require more slipping to attain 4000 odd rpm for getting the vehicle to move while a diesel engine will require only about 2000 odd rpm (considering that both are average hatchbacks we find). In such a case, how would you say that a petrol engine is more powerful at a lower rpm?
On a moderate incline, once the car is moving at 1 to 3 kmph, in a WagonR you can release the clutch fully - engine wont stall even though rpm is less than 1000.

If you try the same thing in a diesel car, engine will stall - you have to keep slipping the clutch until the rpm at wheels reaches a respectable number.


My point is this - if you happen to be driving in the turbolag regime (less than 1750 for a Tata, less than 2000 for a Maruti, less than 1200 for Figo/Ford) in a diesel - you are going to regret not having a petrol. This can happen very easily in stop and go traffic on an incline.
vina is offline   Reply With Quote
Old 9th May 2011, 17:28   #179
BHPian
 
teknophobia's Avatar
 
Join Date: Mar 2008
Location: Ahmedabad
Posts: 319
Thanked: 22 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by vina View Post
On a moderate incline, once the car is moving at 1 to 3 kmph, in a WagonR you can release the clutch fully - engine wont stall even though rpm is less than 1000.

If you try the same thing in a diesel car, engine will stall - you have to keep slipping the clutch until the rpm at wheels reaches a respectable number.


My point is this - if you happen to be driving in the turbolag regime (less than 1750 for a Tata, less than 2000 for a Maruti, less than 1200 for Figo/Ford) in a diesel - you are going to regret not having a petrol. This can happen very easily in stop and go traffic on an incline.
That's not the case, sorry. Nothing much else to say except that either a) you have no idea what you're talking about or b) you're deliberately trolling.
teknophobia is offline   Reply With Quote
Old 9th May 2011, 17:35   #180
Senior - BHPian
 
mayankk's Avatar
 
Join Date: Apr 2010
Location: New Delhi
Posts: 4,115
Thanked: 3,489 Times
Default Re: Torque vs BHP?

Quote:
Originally Posted by vina View Post
On a moderate incline, once the car is moving at 1 to 3 kmph, in a WagonR you can release the clutch fully - engine wont stall even though rpm is less than 1000.

If you try the same thing in a diesel car, engine will stall - you have to keep slipping the clutch until the rpm at wheels reaches a respectable number.

Shouldnt the bold bits be flipped?
mayankk is online now   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
My Kleemann K4 : 650 BHP and 900 NM of torque! gemballa Super-Cars & Imports in India 172 23rd November 2013 09:54
200 BHP and torque up to 400Nm Fortuner ! hail Pete's! jkdas Modifications & Accessories 13 18th September 2009 15:57
torque vs rpm vs bhp graph : DDIS 1.3 MJD goandude Technical Stuff 2 27th July 2009 11:07
Actual bhp & torque. veyron-w16 Technical Stuff 0 22nd December 2008 22:50
Torque and BHP Subbu Technical Stuff 2 9th August 2006 15:14


All times are GMT +5.5. The time now is 00:35.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks