sgiitk

Petrol v Diesel

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I would like members to comment on the Petrol v Diesel issue. I would suggest the following framework:

1. It is agreed that Diesels are more Fuel Efficient. (so please no discussion on this)

2. We should limit ourselves to modern diesels (i.e. Common Rail / PD). Let us keep Indirect Injection engines etc. out.

I would suggest some broad heads (vis a vis equivalent petrols) for opening the discussion:

1. Performance

2. Noise-Vibration-Harshness

3. Engine durability

4. Maintenance costs

Another point worth discussing is: Are diesels with their higher torque and lower power bands more suitable for Automatic Transmissions?

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Diesels have longer life, properly designed diesels from Honda or Toyota are as smooth and quiet as their petrol counterparts, diesels are a darling to drive in traffic, with their instantaneous torque, they need lesser downshifts and the engine has lesser chances of getting lugged as well. Automatic or manual, diesels of today are it, even on highways, they are less highly strung than their petrol counterparts.

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If the diesel cars were priced like petrol cars, diesel cars would outsell petrol cars. This can be true even if the prices of petrol/gasoline and diesels were same, because diesel has good fuel efficiency and performance whil petrol has less NVH.

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People Buy diesel bease it had very less expensive Running cost and technology has soo much improved that the Diesel just feels as powerful as Petrol one , so people who drives arund or above 1200 kms just go for Diesel one ,

 

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diesels make you spend a little more on maintenance and are vibrate a little more but they make more sense because of the fuel efficiency and the lower cost of diesel. nowadays, the diesel versions of some cars are better performers than their petrol siblings

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Just on a different note, I was wondering what if the car makers start giving turbo charged petrol engines at affordable price, like Fiat 1.4L T-jet petrol engine that produces 120bhp and 200Nm torque. If Fiat does offer it for Grande Punto and Linea sooner or later, other car makers might also be forced to give petrol engines as powerful as diesel engines.

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Just on a different note' date=' I was wondering what if the car makers start giving turbo charged petrol engines at affordable price, like Fiat 1.4L T-jet petrol engine that produces 120bhp and 200Nm torque. If Fiat does offer it for Grande Punto and Linea sooner or later, other car makers might also be forced to give petrol engines as powerful as diesel engines.[/quote']

 

Dont think the Fit will Launch turbo Petrol for thier Punto might be For thier Linea

till then

 

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Ah! most important thing Diesels have less power band so quiet less on power.

 

It was true with old diesel engines. Not anymore with the new common rail, fixed/variable turbo charged diesel engines, that nowadays come with any new diesel car model.

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A typical diesel may have decent power from say 2000 to 4000rpm. The petrol will have power from  2500 to 6000rpm. Hence the power band is about 2x for diesel, while it is almost 2.5x for petrol. The higher torque of the diesel compensates somewhat, but is let down by the Turbo lag if revs are allowed to drop any further.  Thus on the face of it the diesel should need more gear changing than the equivalent petrol.. Hence my remark in the original post about diesels being more suitable for automatics.

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Ah! most important thing Diesels have less power band so quiet less on power.

 

It was true with old diesel engines. Not anymore with the new common rail' date=' fixed/variable turbo charged diesel engines, that nowadays come with any new diesel car model.
[/quote'] Well the tachy has max reading of 5krpm but its pertol one has 8krpm

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Well the tachy has max reading of 5krpm but its petrol one has 8krpm

Most engines become harsh and run out of steam before the redline. Most passenger cars have redlines about 500 rpm above the indicated figure in my post.

You should look for the red (forbidden) and sometimes yellow bands (permissible, but not recommended). The tach displays you saw are just manufacturing artifacts - while petrol tachs just take the signal from the ignition diesels need

more electronics and are thus manufactured separately. Manufacturers put the displays to 8000/5000 (one size fits all) and then add these coloured bands indicating the actual permitted rpms'.

It is rare to find petrol cars going much about 6500 rpm. Incidentally, the old Fiat 128 had a redline of 8300rpm way back in 1976!

sgiitk2007-11-21 16:07:43

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Honda VTEC engines rev to their limit of 8000rpm with ease without any ill effects to their engine, infact most Japanese engines love to be revved and reward their users with lots of bliss at redline. The Japanese engines are developed with lighter exotic alloy flywheels and parts compared to counterparts from elsewhere and usually are short stroke engines leading to their rev happy nature. The original rev champ was 1965 Honda S800 http://en.wikipedia.org/wiki/Honda_S800

One English auto journalist still has this car and even though most in those days were scared from high RPM, this car proved that it can indeed be engineered. The car had phenomenal performance due to its light body, typical Japanese slick gear shifter and excellent power to weight ratio. This meant it managed to keep ahead of its counterparts with ease, something later achieved by the 8500rpm Honda NSX.

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Honda VTEC engines rev to their limit of 8000rpm with ease without any ill effects to their engine' date=' infact most Japanese engines love to be revved and reward their users with lots of bliss at redline. The Japanese engines are developed with lighter exotic alloy flywheels and parts compared to counterparts from elsewhere and usually are short stroke engines leading to their rev happy nature. The original rev champ was 1965 Honda S800 http://en.wikipedia.org/wiki/Honda_S800

One English auto journalist still has this car and even though most in those days were scared from high RPM, this car proved that it can indeed be engineered. The car had phenomenal performance due to its light body, typical Japanese slick gear shifter and excellent power to weight ratio. This meant it managed to keep ahead of its counterparts with ease, something later achieved by the 8500rpm Honda NSX. [/quote']

Thanks for the information, dude. These Japanese engines are simply awesome. They make possible the unthinkable.

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Honda VTEC engines rev to their limit of 8000rpm with ease without any ill effects to their engine' date=' infact most Japanese engines love to be revved and reward their users with lots of bliss at redline. The Japanese engines are developed with lighter exotic alloy flywheels and parts compared to counterparts from elsewhere and usually are short stroke engines leading to their rev happy nature. The original rev champ was 1965 Honda S800 http://en.wikipedia.org/wiki/Honda_S800 One English auto journalist still has this car and even though most in those days were scared from high RPM, this car proved that it can indeed be engineered. The car had phenomenal performance due to its light body, typical Japanese slick gear shifter and excellent power to weight ratio. This meant it managed to keep ahead of its counterparts with ease, something later achieved by the 8500rpm Honda NSX. [/quote']

Thanks for the information, dude. These Japanese engines are simply awesome. They make possible the unthinkable.

You are most welcome.

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Gurkha: I cannot agree more. My point was that the generic tacho's developed will cater to (almost) all petrol engines if they have electronics designed to work up to 8000rpm. Then the manufacturer only has to give it a custom dial without changing the guts. With modern electronically controlled engines, you cannot over 'rev. As for the short stroke engines, they are the ones with the best power to weight, but often have low torque at lower revs. I had mentioned the good old Fiat 128 from the 1970's, which had a really short stroke.

Also, it adds to my point about the higher power band ratio (max revs to min revs) in petrols. Would you like to comment about the natural suitability of diesels for automatic transmissions?

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The lower end power problem of short strokes have been well taken care by technology like VTEC, dual intake and exhaust port tuning thanks to the ECU controlled FI engines of today. Now they all combine to deliver a very tractable powerband all the way from bottom to top. Of course my big block Trans Am with 8L V8 would spin my 255 tires with ease and you can't compare a 2L engine giving the same torque at low end but then engines like the turbo 2L in Mitsu Evo churn out 400bhp with ease, combined with way superior power to weight ratio, they rule tne roost. Of course a hyper short stroke engine needs a slick gearbox and really good driver who can keep up the revs to stay in the powerband, its not everyone's cup of tea and neither are turbo engines.

Diesels work well with auto trannies due to their superior powerband and so do US V8s with their instantaneous torque. Diesels with manual shifts are fun as well as you they can be lugged with ease and don't need frequent shifting.Gurkha2007-11-22 14:31:10

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The lower end power problem of short strokes have been well taken care by technology like VTEC' date=' dual intake and exhaust port tuning thanks to the ECU controlled FI engines of today.

....

Of course a hyper short stroke engine needs a slick gearbox and really good driver who can keep up the revs to stay in the powerband, its not everyone's cup of tea and neither are turbo engines.

Diesels work well with auto trannies due to their superior powerband and so do US V8s with their instantaneous torque. Diesels with manual shifts are fun as well as you they can be lugged with ease and don't need frequent shifting.[/quote']

Thanks for expanding on the theme. We seem to agree that Normal short stroke petrols will in general have their power bands starting quite a bit further up.

The better suitability of diesels to auto's, due to their (far) higher low end torque and smaller power bands was what I had in mind from the outset.

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This really is matter of many parts - premium charged for the diesel over petrol, taxation matters (in UP petrol cars attract 2.5% while diesels are taxed at 4.5%), insurance costs (almost all diesels have larger engines than their petrol cousins, so may cost more to insure), maintenance costs etc.

One cannot come up with a simple figure which fits all. The general thinking is about 15,000-20,000 km per annum will be a good guess.

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...almost all diesels have larger engines than their petrol cousins' date=' so may cost more to insure), maintenance costs etc. 
[/quote']

 

Which car are you talking about? As far as I know, almost all the cars come with smaller diesel engines than their closest petrol siblings in terms of power and torque (e.g. fiesta, Verna, Swift, etc.) If getz prime or optra magnum gives bigger diesel engines, that is because the diesel siblings are placed in a different leage.

 

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