[anilisanil]

Originally Posted by alpha1

It does not.
Let say you are doing 40 kmph at 3rd gear. at 2000 RPM.
In diesel car - if you need to race to 120kmph you will need to increase the engine RPM to 2000 x 120/40=6000 RPM.

Sadly there are no diesel engines that can rev that high.
So you will shift to higher gear.

On my petrol car I can go upto 140, without changing the gear, because my petrol engine can rev till 7000 RPM.

And ground speed is directly related to engine speed and gearing ratio.
What else can it depend on?

Thanks mate, some how I inadvertantly missed this, I just assumed things for lower speeds!! Thanks for clarifying that technically!!

Though at 3rd gear and 2000 rpm a diesel would be doing more than 40 kmph, I got the gist

[oxyzen]

If we consider the current Diesel vs Petrol comparison in India.
Swift Diesel = Swift petrol
Ritz Diesel = Ritz Petrol
Polo Diesel < Polo Petrol
Micra Diesel >> Micra Petrol
Figo Diesel >> Figo Petrol
Punto Diesel = Punto 1.4 >> Punto 1.2
I20 Diesel >> I20 Petrol
Fiesta Diesel << Fiesta Petrol
Verna Diesel >> Verna Petrol
Linea Diesel > Linea Petrol
Optra Diesel >> Optra Petrol
Vento Diesel >> Vento Petrol
Corolla D <<< Corolla Petrol

Leave out turbo petrols and:-
So it is 7 for diesel and 3 for petrol. Thats a white wash.
I too voted for petrol be cause nothing comes close to the joy of revving it to high RPM but India's Car scenario states otherwise.

Originally Posted by alpha1

Let say you are doing 40 kmph at 3rd gear. at 2000 RPM.
In diesel car - if you need to race to 120kmph you will need to increase the engine RPM to 2000 x 120/40=6000 RPM.

Sadly there are no diesel engines that can rev that high.
So you will shift to higher gear.

On my petrol car I can go upto 140, without changing the gear, because my petrol engine can rev till 7000 RPM.

And ground speed is directly related to engine speed and gearing ratio.
What else can it depend on?

You are right theoritically but it does not work that way. Petrol and diesel have different gear ratios.
In a petrol you can do 40 kmph at 3rd gear. at 2000 RPM.
But in diesel it will be somewhere around 45-50 kmph at 2000 RPM.

Diesel already have the advantage of torque so they can afford to use higher gearing.

[anilisanil]

Originally Posted by alpha1

And ground speed is directly related to engine speed and gearing ratio.
What else can it depend on?

If you are taking about one car yes, if you are comparing different cars, the ground speed is dependent on engine speed, tire size, gear ratio and final drive ratio.

Since gear ratios differe significantly for diesel and petrol we cannot compare with RPMs directly.

However you are right, one can reach higher speeds in lesser gear for a Petrol engine and for most this is fun and exhilirating.

Originally Posted by oxyzen

If we consider the current Diesel vs Petrol comparison in India.
Swift Diesel = Swift petrol
Ritz Diesel = Ritz Petrol
Polo Diesel < Polo Petrol
Micra Diesel >> Micra Petrol
Figo Diesel >> Figo Petrol
Punto Diesel = Punto 1.4 >> Punto 1.2
I20 Diesel >> I20 Petrol
Fiesta Diesel << Fiesta Petrol
Verna Diesel >> Verna Petrol
Linea Diesel > Linea Petrol
Optra Diesel >> Optra Petrol
Vento Diesel >> Vento Petrol
Corolla D <<< Corolla Petrol

Leave out turbo petrols and:-
So it is 7 for diesel and 3 for petrol. Thats a white wash.
I too voted for petrol be cause nothing comes close to the joy of revving it to high RPM but India's Car scenario states otherwise.

The question I asked was for similar displacement engines, in most cases where diesel scored above petrol the diesel has a higher cc!!

Originally Posted by oxyzen

You are right theoritically but it does not work that way. Petrol and diesel have different gear ratios.
In a petrol you can do 40 kmph at 3rd gear. at 2000 RPM.
But in diesel it will be somewhere around 45-50 kmph at 2000 RPM.

Diesel already have the advantage of torque so they can afford to use higher gearing.

I agree with you completely, but as I said may be he was just intending to give an example, petrols are fun for revving up (for many) however, I like my engine the diesel way, lots of torque!!!

[alpha1]

^ Yes, my intent was to illustrate in simple terms that in same gear you can have a large speed range.

Also higher revs sounds/feel more "racy" ... aint it?

[volkman10]

See attached document on the future (2015)trends in diesel engines( page 1)

• cars could exceed 5.2 l/100km
• reduced emissions
• quiet and effective combustion
• improved fuel economy
• could improve fuel economy upto 43% compared to comaprable petrol engines
• lower operating cost

Cheers!

[udiboy]

Originally Posted by alpha1

It does not.
Let say you are doing 40 kmph at 3rd gear. at 2000 RPM.
In diesel car - if you need to race to 120kmph you will need to increase the engine RPM to 2000 x 120/40=6000 RPM.

Sadly there are no diesel engines that can rev that high.
So you will shift to higher gear.

On my petrol car I can go upto 140, without changing the gear, because my petrol engine can rev till 7000 RPM.

And ground speed is directly related to engine speed and gearing ratio.
What else can it depend on?

isnt the calculation based on the assumption of linearity, which we are pretty sure is never the case, the torque/power delivery is not a straight line but a curve!!!

[alpha1]

Originally Posted by udiboy

isnt the calculation based on the assumption of linearity, which we are pretty sure is never the case, the torque/power delivery is not a straight line but a curve!!!

It was just a "back of the envelope" calculation with simplifying assumptions.


But what I wrote is visible and perceptible also to a large extent.