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Old 5th October 2005, 21:55   #16
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Default torque curve gives a clearer picture

Torque versus rpm characteristic of an engine can provide us more details about the performance, rather that peak-torque or peak-power numbers which give only a rough idea. Following link has a good explaination:

http://www.e31.net/torque_e.html

Gear ratios and the total weight of the car will further govern the acceleration (pick-up)
that will be "felt".

another link on the same page shows gear diagrams, which illustrate how tall or short
gear ratios are -

http://www.e31.net/navtechnik_e.html



I would like to see such curvs for cars presently available in indian market, especially
c-segments like baleno, petra, icon etc (since I am planning to buy one....)
Do manufacturers provide such information?
If not, does anyone know about any other authentic source?

Thanks in advance....

Last edited by santosh.s : 5th October 2005 at 22:00. Reason: correction to the 2nd link
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Old 6th October 2005, 11:54   #17
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santosh, torque curves etc are generally there in the car manuals...so if you can grab hold of one from a friend etc....you can have a look (atleast there is a torque curve in my Indica manual so safe to assume others will have it)
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Old 6th October 2005, 15:16   #18
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hey guys, i too have seen these graphs for wagonr and other cars, but can u tell me how to read them?
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Old 6th October 2005, 15:57   #19
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Its a graph, so its X and Y axes
On the vertical is the torque/power and horizontal axis is the RPM
So if you travel from left to right, the RPM is increasing and you can see what that does to your torque/power figures......

It will have a hump in the middle , which is the RPM band where the torque is high
This is "generally" in the 2500-4000 rpm range....I said generally so dont blame me if its not the case :-)
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Old 6th October 2005, 18:13   #20
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Quote:
Originally Posted by ananthkamath
Roughly speaking, Bhp = Torque x Speed
what does that speed indicate??which speed did u mean..the vehicle speed ??

Last edited by kphilip : 6th October 2005 at 18:29. Reason: Didin't qoute
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Old 6th October 2005, 18:17   #21
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Quote:
Originally Posted by kphilip
what does that speed indicate??which speed did u mean..the vehicle speed ??
Speed would be the RPM ..
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Old 6th October 2005, 18:22   #22
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Default Effect of AC on power

Trying to adding another angle to this discussion ..

I admit I do not have much clarity regarding this ..

My understanding is that aircons sap some of the power of the engine .. i.e. if the engine is producing X bhp (torque x RPM) , then the aircon uses up some of that power , say Y .. is this correct ?

If so, the available power to move the car is basically X-Y .. is this correct ?

If so, where does the power come from when the car is stationery ? I mean then there is only RPM , no torque , right ?
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Old 6th October 2005, 18:33   #23
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Hi Raja,
if you run ur engine at low RPM, chances are your engine is using all of the fuel supplied in each stroke. if engine speed increases, you can shift to higher gear so that u can still drive at low RPM.

a fictious example.
1. speed 20kmph, first gear,, RPM 1000
2. speed 40 kmph, first gear, RPM 2000 (now engine is revving faster, and is capable of providing more power, which is torque X RPM which you don't need) so u shift to second gear
3. speed 40kmph, second gear RPM 1500 (since the engine is loaded, you need a little higher RPM, remember at second you have to keep ur accelerator a li'l higher than normal)

this will mean less revolutions per kilometer, and hence less fuel consumption. chart comes in handy if you want to see whether at 2000 RPM ur power will be double of 1000, or something diff.
basically power at 1000 RPM =torque at 1000RPM X 1000
and power at 2000 RPM =torque at 2000RPM (which cud be derived from the chart) X 2000. so it's not necessarily double of first case.

regd engine life, if u keep it at (unnecessary) high RPM, friction will be high, and so is wear and tear.
if u keep at low RPM the speed will be low, but the pressure buildup in chamber will be higher. as far as I understand, that will not pose a big hazard to the sealing in combustion chamber. but not recommended in running in period.
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Old 6th October 2005, 18:40   #24
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shuvc,
I am also weak in auto electronics. let me guess.

if engine is running, that means there is an RPM, and power comes from that.
if engine is dead, then obviously it's not supplying power, it might be coming from battery.

whe engine starts runing, it replenishes the battery, as well as powers the AC. so now u can keep an account of the missing BHPs. :-)
once battery is full, engine only has to power the AC.

let's wait for an expert on that. it cud be more complicated.

Last edited by vivekiny2k : 6th October 2005 at 18:42.
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Old 6th October 2005, 19:12   #25
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Quote:
Originally Posted by vivekiny2k
let's wait for an expert on that. it cud be more complicated.
Hmm .. so it comes from the battery ..
You are right .. lets wait for the gurus to throw more light on this .
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Old 6th October 2005, 19:15   #26
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Quote:
Originally Posted by vivekiny2k
Hi Raja,
if you run ur engine at low RPM, chances are your engine is using all of the fuel supplied in each stroke.
That's good ? or bad ?

Quote:
Originally Posted by vivekiny2k
if u keep at low RPM the speed will be low, but the pressure buildup in chamber will be higher. as far as I understand, that will not pose a big hazard to the sealing in combustion chamber. but not recommended in running in period.
But don't they specify not to over revv the engine during the running in period ? Do they specify minimum revvs too ?

Strangely, during a Baleno test drive, the sales guy asked me to floor it .. I said should one do that in a new car ? He seemed to have not heard of running in period .. he said the Baleno does not require any running in !
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Old 7th October 2005, 01:17   #27
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Quote:
Originally Posted by shuvc
That's good ? or bad ?



But don't they specify not to over revv the engine during the running in period ? Do they specify minimum revvs too ?

Strangely, during a Baleno test drive, the sales guy asked me to floor it .. I said should one do that in a new car ? He seemed to have not heard of running in period .. he said the Baleno does not require any running in !
that is correct...Baleno does not come with any running in instructions..... The new engines are built to fine tolerances and are also prerun for many hours before they are installed....so they do not require running in again...

On the other hand...the same isnot true of the entire car per se...so generally not a bad idea to go slow for the first 1500 km anyway (play it safe and dont cross 3000 rpm)
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Old 7th October 2005, 11:53   #28
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vivekiny2k and shuvc, in youor AC discussion, why are you factoring in the battery ?
Are you guys talking abt a hybrid car or petrol car

yes shuv, some power is lost in running the AC but I didnt understand what you meant by when car is stationary, no torque
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Old 7th October 2005, 12:13   #29
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Quote:
Originally Posted by Abhay
vivekiny2k and shuvc, in youor AC discussion, why are you factoring in the battery ?
Are you guys talking abt a hybrid car or petrol car

yes shuv, some power is lost in running the AC but I didnt understand what you meant by when car is stationary, no torque

Power produced by the engine is used for following-

1. To overcome friction of all moving parts in engine itself, transmission etc.
2. To overcome tyre friction. this can not be ignored... everybody must have experienced
how harder it is to pull a bike with a flat tyre(?) Also remember we need to have tyres well inflated
in order to minimize the friction and get better milage
3. To overcome the air friction, this is significant at high speeds, demands aerodynamic
body designs.
4. A/C, brakes, power steering etc. which use engine power for their operation
5. electric power to charge battery, for ignition system. I guess this must be negligible.
6. last but not least to accelerate!

I believe A/C does need quite a big slice of the power. This explains why we feel running
out of poewer and less milage with A/C on.

At idle, 2, 3 & 6 above are out of question and the engine power is consumed for the
rest...

Regarding battery energy, it is used only for lamps, music systems and other electric
devices like power-windows, automatic locks etc. and to start the engine.... unless
of course it is a Reva or a hybrid engine!

Last edited by santosh.s : 7th October 2005 at 12:16. Reason: to add a point
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Old 7th October 2005, 12:31   #30
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well, the only observation being I cud feel the AC vents even when the engine is not started (just turned the key to switch on the panel etc).

may be it's just the fan and not the AC. but there is no place other than battery where it could
draw it's power from.
right?
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