Is BHP Per Ton the Most Relevant Factor For Performance?

[kunal Singh]

Hii all I am creating this thread as I could not find a similar thread where to post this.
This question seems to be constantly in mind (title of the thread). Here are some figures to convey an idea of what I am talking about-

Tata Nexon diesel with 110 bhp and 260nm of torque with 83bhp/ton and 199nm torque/ton does 0-100 dash in 13.75 seconds and a baleno rs with 102 bhp and 150nm of torque with 106bhp/ton and 156nm of torque/ton does the 0-100 dash in 10.25 seconds (data is taken from ACI reviews).

My question is that having a difference if about 30bhp/ton is more significant than a difference of about 43nm of torque /per ton as timings show so what is the real use of that extra torque in nexon?

Please take note my comparison does not involve high tech dual clutch gearbox carrying cars like gt tsi because the lighting quick upshifts do shave of a lot of time and hence quicker acceleration .

 

[kkn13]

0-100 is not the exact method
0-20
20-40
and so on is the correct method

That said turbo petrols have minimal "turbo lag" compared to diesels so its understandeable

Your observation about VW DSG is on point
Its the transmission that makes them feel quicker else there are better engines out there imho

 

[acechip]

Power to weight and torque to weight are reference points. Not absolute markers for deciding anything. A lot is dependent on the engine design, cubic capacity (no replacement for displacement), Even a RWD vs FWD makes a difference. For example, a rear biased, light weight Nano with negligible power to weight and torque to weight ratios can climb an incline easier than a FWD hatch in the typical 800-1000 cc range.
In-gear acceleration is far more important and relevant than 0-100 times. So called auto-journalists and YT videos (e.g, 180 kph on Expressway, etc) are spoiling the ignorant car owners with dangerous content.
What they don't show, is that if a Baleno RS with a full load slows down from 100 to 50, how quickly can it again recover vis-a-vis a similarly loaded car with larger engine capacity but lesser power and torque ratios.

 

[carcommentor]

Hii all I am creating this thread as I could not find a similar thread where to post this.
This question seems to be constantly in mind (title of the thread). Here are some figures to convey an idea of what I am talking about-

Tata Nexon diesel with 110 bhp and 260nm of torque with 83bhp/ton and 199nm torque/ton does 0-100 dash in 13.75 seconds and a baleno rs with 102 bhp and 150nm of torque with 106bhp/ton and 156nm of torque/ton does the 0-100 dash in 10.25 seconds (data is taken from ACI reviews).

My question is that having a difference if about 30bhp/ton is more significant than a difference of about 43nm of torque /per ton as timings show so what is the real use of that extra torque in nexon?

Please take note my comparison does not involve high tech dual clutch gearbox carrying cars like gt tsi because the lighting quick upshifts do shave of a lot of time and hence quicker acceleration .

Higher Torque means you can move more weight so Nexon can easily climb steep slopes and haul 5 guys in car without breaking a sweat. The higher acceleration of Baleno and thus lower 0-100 comes because of lower weight and higher revs. This is evident if you look at the simplified acceleration formula
acceleration = (Torque * rpm ) /weight.
By lowering the weight and by having a higher revolution engine, Baleno is able to accelerate faster. If you want to get more complicated, add gear ratio to the mix!

 

[kunal Singh]

This is evident if you look at the simplified acceleration formula
acceleration = (Torque * rpm ) /weight.
By lowering the weight and by having a higher revolution engine, Baleno is able to accelerate faster. If you want to get more complicated, add gear ratio to the mix!

I do understand that closely stacked gear ratios make for faster in gear acceleration but lower top speed and opposite is true for cars with longer gear ratios.
So for simpler understanding can I assume that nexon is a cruiser that can sustain a particular speed for a long time and baleno as the one which is more of a sprinter.
Here are some more numbers to confuse all of you-

Timings RS Abarth GT tsi

0-100 kph 10.25 9.32 11.02

20-80 kph 9.45 10.44 6.48
(Third gear)

40-100 kph 12.53 13.55 8.10
(Fourth gear)

All timings in seconds.Fgures of TSI gives us an idea that how slick and fast the gearbox (DSG) is and despite the tsi having lowest bhp/ton ratio propels it the fastest in third and fourth gear it absolutely smokes the rs and abarth.

 

[carcommentor]

I do understand that closely stacked gear ratios make for faster in gear acceleration but lower top speed and opposite is true for cars with longer gear ratios.

Both Rev and gear ratio is crucial to acceleration as the maximum speed which can be attained in a gear is determined by the gear ratio. Eg Let’s take the 1st gear ratio of 2, 2.5, 3, 3.5, 4 and 4.5 and Final drive ratio of 3.5. I have taken max rpm to be 7000 and tyre radius including side wall to be 12.43 inches .
Max Speed in Km = ((rpm*60)*(2*tyre radius*3.14)/((gear ratio*final drive ratio)*(12*5280)))*1.60934
In these cases , the maximum speed which can be attained will be 118.964, 95.171, 79.3092, 67.9793, 59.4819 and 52.8728 kmph respectively. Of course the max speed will be less than this due to drag, friction, transmission loss etc.

So for simpler understanding can I assume that nexon is a cruiser that can sustain a particular speed for a long time and baleno as the one which is more of a sprinter.

Yes that's more or less correct.

Here are some more numbers to confuse all of you-

Timings RS Abarth GT tsi

0-100 kph 10.25 9.32 11.02

20-80 kph 9.45 10.44 6.48
(Third gear)

40-100 kph 12.53 13.55 8.10
(Fourth gear)

All timings in seconds.Fgures of TSI gives us an idea that how slick and fast the gearbox (DSG) is and despite the tsi having lowest bhp/ton ratio propels it the fastest in third and fourth gear it absolutely smokes the rs and abarth.

Technically, you don’t need large bhp. To accelerating weight of 1,200kg (car+driver) from 20 to 80 within 6.48 seconds, you just need 57.45 bhp. Whichever car can make the bhp available right from 20 kmph by means of less 'peaky' torque / power curve, better rpm etc will win the acceleration race.

 

[SachinOnTop]

Performance, is not measured with acceleration and top speed only. It's like a complete package with handling and power delivery included in it.
How does a car handle during a quick lane change during high-speed run (not top-speed!) is much more a factor to consider. How does power gets delivered is another. Swift diesels are known for awesome thrust and that 'push-you-back-in-seat' feeling! Verna can also touch good high speed, but in a linear fashion.

And, IMO, 0-100 is not a complete measurement. It should be rather 0-100-0. Braking is often the most neglected part, but is the most crucial one. Think about it.

 

[kkn13]

Performance, is not measured with acceleration and top speed only. It's like a complete package with handling and power delivery included in it.
How does a car handle during a quick lane change during high-speed run (not top-speed!) is much more a factor to consider. How does power gets delivered is another. Swift diesels are known for awesome thrust and that 'push-you-back-in-seat' feeling! Verna can also touch good high speed, but in a linear fashion.

And, IMO, 0-100 is not a complete measurement. It should be rather 0-100-0. Braking is often the most neglected part, but is the most crucial one. Think about it.

Forget Swift, my Ritz was even more punchy than the Swift
Ive yet to come across a car that was that much fun to drive
Before Ritz we owned Swift diesel and petrol

 

[kunal Singh]

Performance, is not measured with acceleration and top speed only. It's like a complete package with handling and power delivery included in it.
How does a car handle during a quick lane change during high-speed run (not top-speed!) is much more a factor to consider. How does power gets delivered is another. Swift diesels are known for awesome thrust and that 'push-you-back-in-seat' feeling! Verna can also touch good high speed

Totally agreed handling needs to be precise the first example that comes to my mind is of alto k10 that car has 92bhp/ton ratio higher than the wagonr powered by the same engine but you feel much better in the wagnor doing speeds of about 90-100kph because steering weighs up alright but in k10 it is very light and any hard manoeuvre or even in straight line stability above 80kph is going to send chills down your spine.
The manner in which the torque is delivered is a personal preference I believe some like it in a linear manner and a few like that pushed in the back feeling gives you that much more sense of going faster.

 

[vijay_968]

...My question is that having a difference if about 30bhp/ton is more significant than a difference of about 43nm of torque /per ton as timings show so what is the real use of that extra torque in nexon?...

I was watching this thread with interest. OP's Final Question "What is the real use of that extra torque in Nexon ?" is rather intriguing. The answers here didn't convince me. As I'm neither a Mechanical nor Automobile Engineer, I poked around and got some answers:


Basics:
In simple terms Torque and Power can be explained as below :

• Torque = Force turning the Wheels
• Power = Rate at which this force is applied

Higher Torque means FASTER Acceleration times

1. Inertia = Weight * (Radius of Gyration)^2 , in lb. ft^2
2. Acceleration Time = [Inertia * (Final RPM – Initial RPM)] "divided by" [ 307.6 x Torque in ft. lbs.] , in Seconds

If Torque is MORE, faster acceleration times and vice versa. Also, if weight (and hence inertia) is LESS, faster acceleration times are achieved. We can safely conclude that TORQUE DOES contribute a lot to acceleration times.


Then HOW does POWER contribute ????
We already saw in Basics above that 'Power helps in applying Torque to the wheels'. Anything wlse ??? Let us also see the specs of both engines:
Boosterjet : Torque of 150 Nm over 1,700 to 4,500 RPM and 102 bHP @ 5,500 RPM
Revotorq .: Torque of 260 Nm over 1,500 to 2,750 RPM and 110 bHP @ 3,750 RPM

Both engines develop their peak Power at 1,000 rpm ABOVE the peak Torque curve. As we concluded above, Torque at wheels helps to build speeds.... BUT, the POWER helps to maintain speeds.


Any others Contribute to Acceleration Times ???
As Torque is delivered from the Engine thro' the Transmission to the Wheels, "the transmission, Friction Losses, and Final Drive Ratio" also contribute a lot, in determining the acceleration times.

I hope above answers are relevant and correct. As others have already written about advantages of higher Torque to achieve better in-gear acceleration times, lesser gear shifts etc, I will skip these.

=============== Trivia Section (for people like ME) ===============

Trivia-1: Higher CC Engine means, "more air can be compressed inside the Cylinder". This results in "more work done, more Torque and more Power" from a higher CC Engine. MEANING, required Job is done in a "much more relaxed manner".
Trivia-2: Lower Gears with "under-drive ratios" have greater Torque. That's why they are used to pull the vehicle from standstill. But, 'Wheel RPM'' is LESS than 'Engine RPM' and this results in lower top speed. Hence, lower gears can be effectively used to limit the Speed of Car, when brakes fail --- shall I say "Engine Braking" ? Am I correct ??
Trivia-3: In "Direct Drive" gear ratio, Engine and Wheels are at the same RPM. Vehicle speed is more than what was in under-drive ratio.
Trivia-4: Gears with "over-drive ratios" deliver lesser Torque to Wheels; This is why, they are unable to pull the vehicle from standstill. However, (while already on move) due to over-drive mode, 'Wheel RPM'' is higher than 'Engine RPM' and this results in higher top speed.
Trivia-5: A vehicle's top speed is limited by weight and aerodynamics, also.
Trivia-6: Mechanical Engineering Formulas For Motion Control --- View attachment Formulas_for_motion_control.pdf

 

[carcommentor]

I was watching this thread with interest. OP's Final Question "What is the real use of that extra torque in Nexon ?" is rather intriguing. The answers here didn't convince me. As I'm neither a Mechanical nor Automobile Engineer, I poked around and got some answers ....
If Torque is MORE, faster acceleration times and vice versa. Also, if weight (and hence inertia) is LESS, faster acceleration times are achieved. We can safely conclude that TORQUE DOES contribute a lot to acceleration times.

While torque is important, what matters more is the bhp, which is a function of torque and rpm. Even with a lower torque and higher rpm, the same power can be attained.
Let me try and explain. The formula for power: BHP = Torque (in ft lb) x RPM / 5252. So to get a 80 bhp, with 250Nm (184.39 in ft lb) Torque, the car needs to rev at 2278.64 but the same 80 bhp can be achieved by a 150 Nm (110.634 ft lb) Torque engine by revving at 3797 rpm.
So with a less powerful engine, higher power and acceleration can be achieved. (refer to the simplified formula in earlier post). This is the principle behind F1 racing cars - they usually have higher revving engine to achieve higher bhp and acceleration from medium torque engines (for their speed class).
Also maximum torque is obtained in 1st gear. However due to gear ratio, you can't achieve the 100 km/h speed in 1st gear. You have to necessarily shift to higher gears, which in turns lowers the torque, so to maintain higher power (bhp) and thus higher acceleration, you need higher rpms.
HTH

 

[jazzyb5454]

great topic, could not understand a word, but felt good after reading.

 

[kunal Singh]

Boosterjet[/I] : Torque of 150 Nm over 1,700 to 4,500 RPM and 102 bHP @ 5,500 RPM
Revotorq .: Torque of 260 Nm over 1,500 to 2,750 RPM and 110 bHP @ 3,750 RPM

Both engines develop their peak Power at 1,000 rpm ABOVE the peak Torque curve. As we concluded above, Torque at wheels helps to build speeds.... BUT, the POWER helps to maintain --- View attachment 236975

From the figures I see nexon hits it's peak power around 3750 rpm whereas the RS does it around 5,500 so this should mean nexon should out accelerate the RS because of higher torque figure and also that it starts to kick in around 1500rpm itself a little before it does in the RS and also that it hits it's peak power much before. So is the weight of nexon the main culprit for having average performance figures despite having the most powerful engine or am I missing something here ?
Gurus please shed some more light.

 

[carcommentor]

great topic, could not understand a word, but felt good after reading.

Imagine the mess when we start discussing Electric Cars next year !

From the figures I see nexon hits it's peak power around 3750 rpm whereas the RS does it around 5,500 so this should mean nexon should out accelerate the RS because of higher torque figure and also that it starts to kick in around 1500rpm itself a little before it does in the RS and also that it hits it's peak power much before. So is the weight of nexon the main culprit for having average performance figures despite having the most powerful engine or am I missing something here ?
Gurus please shed some more light.

There are 2 other main reasons.
The total power (bhp) produced over the turbo range of Baleno is 1893.75 which is almost twice the total power (bhp) produced over the turbo range of Nexon.
Nexon = (191.766*Range[1500, 2750])/5252 = 996.803
Baleno = (110.634*Range[1700, 4500])/5252 = 1893.75
Note: Torque is in ft lb and the bhp is calculated over interval of 100s Eg : bhp at 1500+ bhp at 1600+ bhp at 1700 + bhp at 1800....

The 2nd obvious reason is when Peak power is reached, Nexon rpm is only 3750, so if we ignore gear ratio, transmission etc, the distance covered by nexon per second will be only 68% of Baleno.
nexon distance per sec = (3750 x 2 x Pi x tyre radius)/60;
Baleno distance per sec = (5500 x2 x Pi x tyre radius)/60;
nexon/baleno = 0.681 = 68.1%
HTH

 

[vijay_968]

From the figures I see nexon hits it's peak power around 3750 rpm whereas the RS does it around 5,500 so this should mean nexon should out accelerate the RS because of higher torque figure and also that it starts to kick in around 1500rpm itself a little before it does in the RS and also that it hits it's peak power much before. So is the weight of nexon the main culprit for having average performance figures despite having the most powerful engine or am I missing something here ?
Gurus please shed some more light.

As Nexon is a Compact SUV, it is supposed to have more weight. Vitara Brezza weighs at 1,170 kg (50 kg less than Nexon's 1,225 [to 1,250 kg]). THIS weight range is OK for the segment.

The way you have used the word "culprit" along with Nexon's weight, some fan-boys COULD use it against Nexon, as its demand keeps rising. "Vitara Brezza Vs Tata Nexon" comparison would have been MORE APT, for your 1st post in this thread. Vitara Brezza Diesel takes 13.30 Seconds for 0-100 kph (link), which is marginally quicker than Nexon. Again the "weight, torque, transmission, plus gear ratios" come into play for this.

BTW, thanks to THIS thread, I have attempted a proper comparison between "HOT HATCHES in India" in this link (here).