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Old 23rd April 2007, 19:08   #1
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Default BHP,kgm,CC. How are they related?

I understand these terms as

BHP- Horse power-says about the power of the engine.
kgm- Torque- in physics text book as the rotating potential-in auto world the ability to cruise in top gears at slow speeds.
CC- the volume of 'gas' consumed in one cycle in all cylinders.

Now, consider
Indica V2 TC 67 hp-13 kgm- 1405cc for 1T
victa NA 68 hp- 12 kgm-1948cc-for 1.7T

Since V2 TC and victa NA has the same power/torque range, (although different cc's) can a V2 TC engine work on the victa?

How can the sumo victa NA move from standstill with an engine having less than V2TC's hp/kgm rating?

spacio DI NA 60 hp- 16.2kgm- 1956cc
A whopping 3L consumed, but why doesn't the spacio DI engine develop more hp/kgm?

Indica V2 TC 67 hp-13 kgm-1405cc
indigo TDI 62 hp-12.7 kgm-1405cc
I suppose power and torque are inversely proportional for a given cc, but how does this is not true in indigo TDI when compared to V2 TC?

tavera 80hp-19kgm-2499cc
bolero 63.5hp-19.9kgm-2523cc
both are UV's with DI engines, and both turbo charged, how could bolero's hp be so low? (both Kerb weight 1.6T)

Also,
toyota innova 102hp- 20.4 kgm-2494cc-1.5T
tucson CRDi 112hp- 25 kgm-1991cc-1.6T
Nissan X-trail 136hp- 32 kgm-2184cc-1.6T
So what is the additional 500cc actually doing in toyota?
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Old 23rd April 2007, 21:38   #2
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it also depends on how they tune it. the diesel innova being sold in malaysia with the autobox develops 250nm of torque. (25kgm) and 115bhp. same engine tuned diffrently.

as for the victa moving with less torque it also depends at what engine speed the torque is available. it must be much lower in the victa.
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Old 24th April 2007, 00:21   #3
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Quote:
Now, consider
Indica V2 TC 67 hp-13 kgm- 1405cc for 1T
victa NA 68 hp- 12 kgm-1948cc-for 1.7T

Since V2 TC and victa NA has the same power/torque range, (although different cc's) can a V2 TC engine work on the victa?

How can the sumo victa NA move from standstill with an engine having less than V2TC's hp/kgm rating?
By using calculated gear ratios, the required torque can be sent to the wheel.

If a car produces 13kgm (at the crank) has a 1st gear ratio of 3:1 and final drive ratio of 4:1, the total amount of torque reaching the wheels would be 13 x 3 x 4 = 156kgm (at the wheels).

And if another car produces 20kgm (at the crank) has a 1st gear ratio of 2.6:1 and final drive ratio of 3:1, the total amount of torque reaching the wheels would be 20 x 2.6 x 3 = 156kgm.

So whether your car produces 13kgm or 20kgm at the crank, they can be made to produce similar torque figures at the wheels.

Quote:
spacio DI NA 60 hp- 16.2kgm- 1956cc
A whopping 3L consumed, but why doesn't the spacio DI engine develop more hp/kgm?
Unlike other diesels mentioned in your post, the Spacio is Naturally Aspirated which means that the amount air taken into the cylinder is way lower than what a TC'd engine of the same capacity would have been capable of, resulting relatively lower cylinder compression pressure.

When fuel is ignited at higher compression pressure, the force pushing the piston down is greater. This force multiplied by the stroke length gives you the torque produced at the crank.

Higher force doesn't always mean higher torque, by using a longer stroke length, an engine with a lower compression pressure can achieve higher torque figs (but at lower rpms).

However, there are many other factors like cylinder head, piston head, intake/exhaust etc that can affect the way an engine produces it's torque.

Quote:
Indica V2 TC 67 hp-13 kgm-1405cc
indigo TDI 62 hp-12.7 kgm-1405cc
I suppose power and torque are inversely proportional for a given cc, but how does this is not true in indigo TDI when compared to V2 TC?
Well if both engine are identical in their design, it could be the Turbo Boost Pressure that might be varying or the intake/exhaust system. Unless we know all the parameters it's not possible to pinpoint the cause for this diff.

Quote:
tavera 80hp-19kgm-2499cc
bolero 63.5hp-19.9kgm-2523cc
both are UV's with DI engines, and both turbo charged, how could bolero's hp be so low? (both Kerb weight 1.6T)
What we have to see here is the rpm at which the 2 torques are being produced. The Bolero might have sacrificed engine revvs in order to achieve that torque at low rpms. If 2 engine produce similar torque, one at low rpm and the other at a higher rpm, the engine producing torque at higher rpm will obviously have a better bhp fig.

Quote:
Also,
toyota innova 102hp- 20.4 kgm-2494cc-1.5T
tucson CRDi 112hp- 25 kgm-1991cc-1.6T
Nissan X-trail 136hp- 32 kgm-2184cc-1.6T
So what is the additional 500cc actually doing in toyota?
The innova diesel is a bit disappointing wrt to the amount of torque it produces. They prob did this to make the bigger engine a bit more fuel efficient.

But like i mentioned earlier, the transmission plays a major role in deciding how much torque reaches the wheel. So, don't always go by what the engine specs say.

Shan2nu

Last edited by Shan2nu : 24th April 2007 at 00:24.
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Old 24th April 2007, 09:54   #4
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Nice answer shanu, i agree with you.

one more thing i would like to add, that engine specs offer these peak rated figures of BHP & torque in a certain operating band, under certain conditions.

If two engines of same BHp & torque figures are there.But one which produces peak power at a lower RPM will lug more & accelerate early, & will need lower no of gear shifts to keep it in power band.They might have same Vehicle weight.

Further as shanu described this engine output is further multiplied by drivetrain. So a slightly inferior spec engine mated with a better design gearbox & final drive may pull more than an engine appearing superior in specs o paper.

Final better drive experince depends upon power available at drive wheels/weight.
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Old 24th April 2007, 11:01   #5
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The engine producing more torque at less rpm would have less power (rate at which it produces it) and hence slower. It all depends on the power curve and GEARING.
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Old 24th April 2007, 11:12   #6
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Quote:
Originally Posted by srishiva View Post
The engine producing more torque at less rpm would have less power (rate at which it produces it) and hence slower. It all depends on the power curve and GEARING.
I mentioned BHP available earlier will lug more, hence curve will start flatening earlier so more range available & hence lesser gear shifts & more driveablility, as compared to an engine producing workable output in higher rpms thus limiting usable range. hence producing lesser flat area in power curve assuming same redlines for both engines.

ofcourse drive train plays a vital role in harnessing available power optimally.
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Old 24th April 2007, 14:02   #7
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Quote:
The engine producing more torque at less rpm would have less power (rate at which it produces it) and hence slower. It all depends on the power curve and GEARING.
Not always true. An engine producing 200lbft@2000rpm will produce the same amount of power as another car producing 100lbft@4000rpm.

Shan2nu
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Old 24th April 2007, 15:00   #8
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So, in short the rpm at peak torque and the gearing ratio's all have to be considered as well..thanks shan2u.

also the spacio's is 3000cc not 2000cc as mentioned..


Also regarding bolero, i read in overdrive(this month) that it pulls from way lower rpms(they say it can move even 2/3 rd gear from standstill!)
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Old 24th April 2007, 16:48   #9
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Quote:
So, in short the rpm at peak torque and the gearing ratio's all have to be considered as well..thanks shan2u.
Well, actually the torque throughout the revv band (from idle rpm to peak power rpm) should be be considered. This torque band decides how much power the engine produces at various rpms.

The specs you see in brochures and magazines don't say anything about the way a car performs.

The OHC 1.5 is quicker than the OHC Vtec in low rpm rollons, even thought the Vtec has higher Torque and Power figs. Thats bcos max torque and power are achieved only when the high lift cam lobes are actuated. At low rpm, the engine uses it's low lift cam lobes that were designed for better fuel efficiency and not performance. The OHC 1.5 on the other hand uses the same cam profile throughout the revv band. This might give it better low end torque, but on the downside, it sacrifices top end power/torque.

In simple, the OHC 1.5 jogs from idle to redline, while the OHC Vtec walks at low revvs (reducing consumption) and sprints at high rpm (increasing performance). There are some Vtec engines that can walk at low rpm, jog at mid rpm and sprint at high rpm (they're called 3 stage Vtecs).

Shan2nu

Last edited by Shan2nu : 24th April 2007 at 16:55.
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Old 25th April 2007, 10:16   #10
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See following links for some more details:

Physics behind car's movement (Physics behind car's movement)

Torque vs BHP?

Relationship between CC and BHP
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