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Old 17th April 2016, 10:49   #1
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Default How BHP, Torque and power-to-weight ratios can be misleading

Heard of the BRAT PACK? It's the Alto, Kwid and Eon trio.

Let's look at their BHP, Torque and Power to Weight Ratios.

Alto:

Power: 47.34 Bhp @6000 rpm
Torque: 7.03@3500rpm
Power to Weight:65bhp per tonne
0-100 time: 16.92 seconds
20-80 3rd gear: 13.16seconds
40-100 4th gear:22.29 seconds

Eon

Power:55.23 bhp@5500 rpm
Torque: 7.64@4000 rpm
Power to Weight: 77 Bhp per tonne
0-100 time: 17.60 seconds
20-80 3rd gear:16.86 seconds
40-100 4th gear: 26.49 seconds


Kwid

Power: 53.26bhp@5678rpm
Torque:7.34@4386rpm
Power to Weight:80 Bhp per tonne
0-100 time: 17.94 seconds
20-80 3rd gear: 17.47seconds
40-100 4th gear: 29.76seconds


The car with the lowest power, lowest torque and the worst power to weight ratio has the best acceleration and far better roll on times. The Alto with 77bhp per tonne is faster to 100 kmph in 4th gear than the Kwid with 80 Bhp per tonne by a whopping 7.5 seconds!!!
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Old 17th April 2016, 10:55   #2
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

Quote:
Originally Posted by VeyronSuperSprt View Post
Heard of the BRAT PACK? It's the Alto, Kwid and Eon trio.

Let's look at their BHP, Torque and Power to Weight Ratios.
I believe the low end torque of these vehicles determine the acceleration. Higher BHP probably helps in going faster, but the in-gear acceleration is highly determined by the torque. This is based on my knowledge, so please feel free to correct me.

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Last edited by .anshuman : 17th April 2016 at 14:08.
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Old 17th April 2016, 11:01   #3
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All these cars focus more on Fuel efficiency than performance. Alto with lowest power to weight ratio has best performance due to good gear ratios and ECU tuning. Kwid with best power to weight ratio has the best fuel efficiency too. Performance is not solely based on figures, it also depends on how the power is extracted or delivered by good gear ratios and ECU maps.
Cheers!

Last edited by Dr.Naren : 17th April 2016 at 11:03.
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Old 17th April 2016, 11:24   #4
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

Quote:
Originally Posted by VeyronSuperSprt View Post
Heard of the BRAT PACK? It's the Alto, Kwid and Eon trio.

The car with the lowest power, lowest torque and the worst power to weight ratio has the best acceleration and far better roll on times. The Alto with 77bhp per tonne is faster to 100 kmph in 4th gear than the Kwid with 80 Bhp per tonne by a whopping 7.5 seconds!!!
It is all about gearing. A short 3rd gear will give much better 20-80 times in 3rd gear. The shorter the gear, the quicker the acceleration. However the downside is top speed will be compromised. That's why these 3rd and 4th gear slogs are kind of meaningless. No one drives that way.
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Old 17th April 2016, 11:25   #5
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

This is not surprising since the power and torque figures can be misleading and considering that the peak power and torque are being quoted which may never be achieved in real world driving scenarios

The analogy is similar to speaker output being quoted in terms of PMPO .

Coming back to Alto, Eon and Kwid comparison, its evident that alto produces more torque at lower rpms hence more power at lower rpms which explains why it is quicker of the three.

I came across this reddit article when I had similar questions going inside my head few days ago.

https://www.reddit.com/r/cars/commen...for_semiidiots

Quote:
Horsepower = (Torque x RPM) / 5252
As such, the HP and Torque dyno curves will ALWAYS cross each other at 5252 RPM. That's just how the equation works out. Look at this equation for a second and let’s think about it. If you have an engine that makes a huge amount of torque, but it is rotating very slowly with low RPM’s, the Horsepower will be low.
Or, if you have an engine that makes a small amount of torque, but rotates very fast, you could still have a large horsepower number.
If you’ve got the big V8 engine, it makes a lot of torque at low RPM’s, meaning it also has more HP and accomplishes more work in those lower RPMs but it usually has a lower power curve and RPM redline, so the horsepower number in the higher RPMs is limited compared to a motor that could maintain a good torque curve to 10k RPM.
With the small 4-cylinder engine, it makes less torque and therefore HP at low RPM’s with only half as many cylinders, but it usually revs to higher RPM’s and maintains a better torque curve in those RPMs, so the horsepower could still be as high as the big V8 with more torque. If you look at some of the formula one race cars, they often have very small engines that don’t have a huge amount of torque, but they rev to 18k RPM, so their horsepower is crazy high.
So, the horsepower is just a function of the torque at a certain RPM. That's the most important thing to understand from this. THE HORSEPOWER IS JUST A FUNCTION OF THE TORQUE AT CERTAIN RPM’s.
At lower speeds, the engine makes high torque, but it's making that torque less times per minute with low RPM's, so the horsepower is low because less overall work is being done. As the engine RPM's increases past its most efficient point and peak in the torque curve, the torque decreases for each revolution (I’ll explain why later on). However, it's making that torque more times per minute, so the horsepower starts to increase. Even though it's making less force per revolution, it's revolving (and firing) more times per minute, so the overall work being done is greater, giving more power.

Last edited by GTO : 19th April 2016 at 16:27. Reason: Typos
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Old 17th April 2016, 11:42   #6
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Quote:
Originally Posted by VeyronSuperSprt View Post
Heard of the BRAT PACK? It's the Alto, Kwid and Eon trio.

Let's look at their BHP, Torque and Power to Weight Ratios.
Along with the figures you gave given, isn't it fair to mention the weight of each of these cars? I know the are Power to Weight Ratios of each but things would be a bit clear if the weight figures are mentioned.

Acceleration figures depends on the weight of the car too.

Last edited by a4anurag : 17th April 2016 at 12:05.
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Old 17th April 2016, 12:47   #7
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

Quote:
Originally Posted by VeyronSuperSprt View Post
The car with the lowest power, lowest torque and the worst power to weight ratio has the best acceleration and far better roll on times. The Alto with 77bhp per tonne is faster to 100 kmph in 4th gear than the Kwid with 80 Bhp per tonne by a whopping 7.5 seconds!!!
Acceleration depends on torque, but you haven't mentioned torque to weight ratio or even the weight.

How about adding torque to weight ratio and then see whether the conclusion still holds? Edit: I think it does, according to this pic.

Also, engine torque is not the same as torque at the wheels. The ratio at a gear (3rd/4th), the front differential and the radius of the tyre affect the final result.

Last edited by Samurai : 17th April 2016 at 12:57.
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Old 17th April 2016, 13:58   #8
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

These numbers will make more sense, if we were to compare the power & torque curves for all 3 cars, along with the engine rpm at 20kmph, 40kmph, 80kmph, 100kmph.

A lot will depend on "gearing" for roll on acceleration times.

Also, the 0-100 acceleration will also depend on how easy it is to shift from 1st to 2nd to 3rd. Gearbox shift design determines a lot. Witness the acceleration times of Abarth Punto (not-so-nice gearbox, very powerful) being almost the same as Polo GT TSi (superb DSG, not so powerful).
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Old 17th April 2016, 14:00   #9
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

VeyronSuperSprt, In your comparison I see no mention of gear ratios. Choice of gear ratios play a very important role here.

Also, for the In Gear roll on acceleration figures, the spread of the torque all throughout the rev range is more important than the peak torque figure.
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Old 17th April 2016, 14:10   #10
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

Quote:
Originally Posted by Samurai View Post
you haven't mentioned torque to weight ratio or even the weight.
The weight and torque to weight ratios can be arrived from the data given above:

Weight of Alto:

65/47.3 = 1.373

1000 (1 tonne)/1.373 = 728 (weight of Alto)

And so on.

Quote:
Originally Posted by .anshuman View Post

Also, for the In Gear roll on acceleration figures, the spread of the torque all throughout the rev range is more important than the peak torque figure.
Bingo! Was waiting for this. Yes, the real reason is the power delivery of the engine. The Kwid has a flat mid range where it fumbles a bit so in real world situations best indicated by the roll on figures the car doesn't pick up speed like the Alto does. The Alto is punchier and has a more consistent power delivery. That's all there is to it. Suzuki's decades old F8D series engine is still able to hold its own in modern company.
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Old 17th April 2016, 14:18   #11
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

Quote:
Originally Posted by VeyronSuperSprt View Post
Suzuki's decades old F8D series engine is still able to hold its own in modern company.
At the time of facelift, some changes were made to the engine, the power delivery in post facelift Alto 800 is superior to old Alto. I had also mentioned this in the official review:

Quote:
The biggest area of improvement is the peppier bottom end. The Alto's earlier jerkiness is nearly gone, and the engine feels livelier at low speeds. This makes the Alto 800 far easier to drive in urban traffic. The car pulls cleanly from idle speeds and is quick to respond to throttle input. In-city driveability & behaviour have greatly improved and this is exactly where owners will spend a maximum number of driving hours. It must be mentioned that the throttle is sensitive and it's important to maintain a steady right foot for a smooth drive. Midrange performance is similar to the old car, with the motor feeling peppy enough. This Alto is no tarmac burner on the open road though, and you need to really work the engine to keep pace with fast traffic. While it can cruise at 90 - 100 kph all day long, overtaking manoeuvers need to be carefully planned, as nearly every other car on the road has more power. Taking the engine to high rpm isn't a rewarding experience (unlike the revv-happy Alto K10).
Link to post. (Maruti Alto 800 : Official Review)
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Old 17th April 2016, 14:41   #12
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

Suzuki has been continuously modifying its 800cc engine and fitting it in its newer models. The F8D in the new Alto is the latest avatar of the old F8 engine which originally came in the 800.
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Old 17th April 2016, 17:39   #13
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

I cannot agree more. The power/torque figures are used majorly for marketing. They can only give a very general idea of car performance. Another misleading figure is the engine capacity. After upgrading from my Bullet 500 to Duke 390 a lot of people asked me why did I downgrade to lesser power.
Power and engine capacity do not have linear relation. To really understand the car characteristics you need to see first the torque vs rpm graph of the engine and the rpm spreads for the gears.
Ideally manufacturers should be providing this. Or atleast the review sites like in foreign countries but I guess most don't have a dyno :(
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Old 17th April 2016, 20:21   #14
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

Quote:
Originally Posted by VeyronSuperSprt View Post
The car with the lowest power, lowest torque and the worst power to weight ratio has the best acceleration and far better roll on times. The Alto with 77bhp per tonne is faster to 100 kmph in 4th gear than the Kwid with 80 Bhp per tonne by a whopping 7.5 seconds!!!

Well, in a car group people know its futile judging the quickness of a vehicle by the specified parameters alone. Probably will help if car makers actually quoted performance figures on the brochures (I remember my Ford Ikon 1.6 had a 0-100 time mentioned on one brochure).

What you have done great is to make a placeholder for the fact that the general public is usually wrong in judging how "powerful" (generally they are referring to quickness) a vehicle can be based on just the quoted power (and sometimes Torque) figures.

Thanks for bringing this up.
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Old 18th April 2016, 12:58   #15
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Default re: How BHP, Torque and power-to-weight ratios can be misleading

Peak torque figures are the most futile of the lot.
What matters is the flatness of the torque ACROSS the rev range - can you get that from published numbers??
Torque at wheel is very different from torque produces by the engine, and it is torque at wheels that is responsible for driving.

Bhp numbers does make a difference to the top speed figure and acceleration. PROVIDED you know what is the engine bhp AT the particular RPM that you are at. Usually max bhp is produced close to the red line, hence peak bhp is a still a useful figure, as long as you have necessary gearing to allow you to keep the revs near the peak bhp.

Even the Torque/BHP vs RPM numbers may turn out to be futile for daily commute runs. The reason is because only the wide open throttle response is plotted in those graphs. What happens to 50% opening? What about 10%?

Actually if one has the following data with him, he can calculate almost EVERY performance results to a very good degree (top speed, various accelerations, fuel consumption, throttle response, etc):

a) vehicle particulars:
- Mass
- Frontal area
- Drag coefficient
- Friction losses

b) engine particulars:
- WOT torque vs rpm (along with partial throttle response)
- fuel consumption map

c) transmission particulars:
- gearing ratios
- transmission losses
- transmission lag (delay in changing gears)
- wheel radius

It is simple physics.


Quote:
Originally Posted by 1100D View Post
Well, in a car group people know its futile judging the quickness of a vehicle by the specified parameters alone. Probably will help if car makers actually quoted performance figures on the brochures (I remember my Ford Ikon 1.6 had a 0-100 time mentioned on one brochure).

What you have done great is to make a placeholder for the fact that the general public is usually wrong in judging how "powerful" (generally they are referring to quickness) a vehicle can be based on just the quoted power (and sometimes Torque) figures.

Thanks for bringing this up.
Oh boy, just see how many people were unhappy with what Audi has done:
http://www.team-bhp.com/forum/indian...placement.html (Audi's "Dynamic Badging" - Based on performance, rather than displacement)

Last edited by suhaas307 : 20th April 2016 at 12:31. Reason: as requested. :)
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