Power vs Torque : Petrol vs Diesel

Stephen

I must be some kind of freak because I like both. My own car is a 1.8 i-vtec (i.e. the slower SOHC flavour!) Civic and you've really got to keep the revs high to get power out of it but its great fun to drive and revs freely all the way around the clock.

The ould fella drives a 2.2 diesel Accord with the same power output (140bhp) but oh so much more torque. This is great fun in its own way - i.e. just mash the accelerator and off it goes.

Both cars have six-speed manual boxes. The Civic requires you to pretty much keep your left hand clamped to the gearstick at all times and the Accord is pretty much the opposite and I love them both :pac:

Darwin

...In terms of engine performance, I never thought the 1.8 Avensis was any great shakes. It was good but not exciting. I'm rather underwhelmed by anything smaller than a 1.8 petrol anyway. The diesel wiped the floor performance wise. It wasn't even funny how much faster it was, no need to drop down gears or anything like that, just press the loud pedal down more and it was well able to move. Try the same thing in a petrol and you got nothing. The petrol has zero response below about 2000 rpm. Nothing. Zilch. Zip. Zada. Even flooring it got nowhere. By comparison the diesel at only 1,600 rpm was full of enthusiasm and had no difficulty getting up to speed when this was done....

You are leaving out one small point - you're comparing a turbo charged diesel to a normally aspirated petrol engine. Take the turbo out of the diesel and you'll see a different story. Alternatively, take a drive in the new mini Cooper S which uses BMW's new turbo petrol engine that produces 177 lb-ft of torque at only 1600 rpm!

Biro

craichoe wrote: »

It has a Sequential turbo, having a twin turbo lump would cause severe turbo lag.

It's a twin turbo engine, no matter what way you look at it. With a twin turbo set up, you can have either a Sequential set up or parallel set up, but which ever way you go, you still have a twin turbo engine. (non identical twins in seq, if you want to do life-like comparisons! )
When you employ two turbos in a sequential application, like the 535d, it gives you a means to use a bigger turbo than normal for the higher power delivery, which creates a bigger lag, and then you eliminate that lag by using the smaller turbo. So the aim is still more power from the engine, not smoother delivery, even though that's the plus of this layout.

Matt Simis

E92 wrote: »

+1


A lot of people who have posted in this thread evidently drive petrols the way you should drive a diesel. I'm guilty of it myself. Of course for environmentally conscious driving doing what I did isn't going to save the planet. But if you're bothered about the environment then what are you doing trying to put your foot down for a bit of power in any car in the first place? If you're prepared to give a petrol a bit of stick they will reward you for your effort!

If you want something that's pleasant and relaxing to drive, then get the diesel. If you want something that requires a bit of effort on your part, but really rewards those who take it by the scruff of it's neck and a bit of fun to work hard, then petrol is the only option.

You are probably right. Further down that track, people keep quoting performance car specs, reviews etc while comparing them to their real world driving of A-B "puff puff" everyday cars.

We are on our second V6 Twin Turbo Petrol, overtaking in it is flooring it, engine roars, climbs to 6k rpm and 80MPH and your safely and quickly infront.

Overtaking in the V10 TDI is like flying a rocket, it cruises along with nothing but wind noise, when you goto overtake it literally blasts you into the seat (at 1800RPM) and climbs to 80MPH faster than you can look down to check. You stop accelerating half way through and coast infront spotting the brakes. It will rev to 4800ish, but there really isnt any need (or point).

maidhc

E92 wrote: »

The best comparison is still bhp then. Torque is great, but high revs and bhp is just as good!

Try the hill from Dunkettle towards glanmire on the N8...

...then tell me torque doesn't matter.

Every time you will change up in the petrol you will notice the distinct lack of torque back up.

The key for speed in a petrol is engine speed and momentum. You don't have to worry as much about this in a diesel as the engine has more force at the crank and as such is far more forgiving.

E92

Cyrus wrote: »

i dont know why everyone wants to see a 530i vs a 530d

in e39 guise at any rate, despite the delusions of the 530d owners, a std 530i was quicker than a standard 530d in 9 out of 10 situations.

From what ive seen the 335i is a better car than the 335d aswell, bit of course its horses for courses,

i do very little mileage so i would never take a derv over a petrol

Well the 335i's engine won 3 awards last year in the International Engine of the Year Awards 2007(best 2.5-3.0, overall winner and best new engine), while the 335d's engine won.....none. It won the best 2.5-3.0 the year in 06 and 05 though. In the 2.5-3.0 engine category, the 335i's engine was first, the 335d's was second and third was the engine found in the X3 3.0si and 730i(the 330i and 530i have a newer engine). That to me says the 335i is a better choice. Petrols at high revs are every bit as good as diesels at low revs. Though the 335i has 295 lb ft from only 1,300 rpm all the way up to 4,900 rpm so that must combine the best of both engines performance wise:D!

There is indeed a 535i on sale in the US, it uses the same engine in the 135i and 335i here. The best comparison for the 535d would be the 540i. The 540i has 20 bhp more than the 535d at 306 bhp.

A 530i has 272 bhp, a 530d has 233 bhp, so a 530i should still wipe the floor around the Top Gear test track against the 530d.

Biro

Matt Simis wrote: »

It will rev to 4800ish, but there really isnt any need (or point).

True. Nothing bugs me more than someone driving a diesel like a petrol. Really annoying.

BrianD3

craichoe wrote: »

The pollution angle on diesels being worse than petrol .. its completely subjective, you can mash stats any way you want. Yes, diesel contain Particulates which are carcenogenic, but so is every other material we use thats derivied from crude oil.

If your so concerned that Diesel causes cancer, then don't drive a car at all, because burning Petrol causes cancer too and while your at it, don't use any more plastic containers at home, keep your food outside

Agreed. Also I remember when unleaded petrol became widely available here in the late 80s/early 90s I read lots of articles talking about increased levels of benzene in the fuel causing cancer. There were photos of people filling up their cars with fumes coming off it and dramatic headlines about people breathing in deadly carcinogenic benzene.

Not saying that there is not truth to it (I don't know either way, I'm a scientist but that isn't my area) Similarly I would be dubious when I read about diesel causing "80,000 deaths" in Europe..

I've read plenty of the anti diesel stuff, some of the diesel causes x number of deaths brigade say that there are no carcinogens in cigarette smoke and that the cigarattes cause cancer idea is all a big conspiracy. Also I believe that a prominent anti-diesel researcher who's research is often quoted/referenced is also a Holocaust denier. Take from that what you will.

craichoe

Biro wrote: »

It's a twin turbo engine, no matter what way you look at it. With a twin turbo set up, you can have either a Sequential set up or parallel set up, but which ever way you go, you still have a twin turbo engine. (non identical twins in seq, if you want to do life-like comparisons! )
When you employ two turbos in a sequential application, like the 535d, it gives you a means to use a bigger turbo than normal for the higher power delivery, which creates a bigger lag, and then you eliminate that lag by using the smaller turbo. So the aim is still more power from the engine, not smoother delivery, even though that's the plus of this layout.

Point taken, just twin turbo implies 2 turbos that are the same i.e. twins

E92

The limits for Particulates and Nitrous Oxide for diesels are sky high compared to petrols. NOx is something like 5 times higher for diesels IIRC. These pollutants make the air we breathe worse and cause cancer. That is not an opinion. That is a fact. Every unit of diesel burned produces 13% more CO2 than the same quantity of petrol. That's not an opinion either. That is also a fact.

Petrols are worse for CO2, much worse for CO, but better for everything else. That's not an opinion. That's a fact:).

In the US, where emissions standards are the same for both fuels, we find that the only diesels on sale there are the Merc diesels(which don't comply with the Californian standards), and a handful of others in pick ups and 4X4s. If diesel was as clean as petrol, then there would be diesels sold there. The new diesels from Merc(and shortly other makes) use AdBlue, which comes from that great source olf greeness, natural Gas, a non renewable resource.

A diesel that meets the US standards is cleaner than a petrol, because of the lower CO2(though a lot of the mpg advantage disappears). Diesels here are cleaner if you're selective with the info you want to use.

BrianD3

cause cancer. That is not an opinion. That is a fact

Facts are hard to come by in this debate. Would you argue that cigarette smoke DOESN'T cause cancer? Because many regard that as a "fact" too.

A combination of flawed scientific research, poor knowledge/use of statistics, vested interests, people with agendas, media manipulation makes it hard to know what to believe.

I was just reading the other day that Grapefruits cause cancer in women. Is that a fact? The Irish Independent thought it factual enough to publish it in their health supplement

PS i am not suggesting that you are wrong about diesel exhaust containing high levels of particulates and NOx. These can be easily measured. However the actual effect of diesel exhaust on a human population is much harder to determine.

Panda Moanium

E92 wrote: »

If you drive a petrol like you drive a diesel, you're bound to think they suck.

A lot of people who have posted in this thread evidently drive petrols the way you should drive a diesel.

You're quite right. But the fact of the matter is that your typical driver isn't going to drive a petrol car to get the maximum power out of it. Not unless they want to be labelled as a boy or girl racer very quickly.

People just aren't comfortable revving much beyond 3,000 rpm. They feel they are trashing the engine and that it is destroying fuel consumption returns. And (ref boy racer comment above), that its somehow anti-social.

That's why diesels are better for everyday driving. Because the power comes within a rev range that people are comfortable using.

craichoe

The limits for Particulates and Nitrous Oxide for diesels are sky high compared to petrols. NOx is something like 5 times higher for diesels IIRC. These pollutants make the air we breathe worse and cause cancer. That is not an opinion. That is a fact. Every unit of diesel burned produces 13% more CO2 than the same quantity of petrol. That's not an opinion either. That is also a fact.

Petrols are worse for CO2, much worse for CO, but better for everything else. That's not an opinion. That's a fact:).

In the US, where emissions standards are the same for both fuels, we find that the only diesels on sale there are the Merc diesels(which don't comply with the Californian standards), and a handful of others in pick ups and 4X4s. If diesel was as clean as petrol, then there would be diesels sold there. The new diesels from Merc(and shortly other makes) use AdBlue, which comes from that great source olf greeness, natural Gas, a non renewable resource.

Taking California as an example, at one point they put legislation in place that required all manufacturers selling cars in the state of california to have a zero emissions alternative. Hence the introduction of the Electric car, which in theory sounds great, no emissions right ? .. Wrong. Instead you move the problem down the road to the power generation point, on top of that your losing more energy in the conversion (which is true of all energy conversions). On top of that you have to dispose of the batteries which contain toxic substances that are very harmful to the environment.

As a result, California withdrew the legislation.

Whatever is "Harmful to humans and the Environment" will change every decade. At one point in time Cigarettes were considered to be safe, now we know of course they increase the risk of lung disease.

You can spin anything any way you like depending on who you talk to. The point of taxation at the moment is to lower Co2 so we dont have a big whopping bill.

maidhc

Panda Moanium wrote: »

People just aren't comfortable revving much beyond 3,000 rpm. They feel they are trashing the engine and that it is destroying fuel consumption returns.

...they are destroying fuel consumption! The faster the engine turns the greater throughput of fuel.

Matt Simis

Since this is heading down the usual "which will kill you faster: diesel or petrol", path (again), here are some other figures pulled from equally contradictory and random research, WW sources (some are WHO):

-820,000 people die a year from air pollution. Car traffic accounts for 80k of that
-Fuel in ships is 2000x (yes, 2000 times more) polluting then petrol or diesel, each freighter has an engine similar to a power plant (which are regulated, ships arent), there are over 55k such ships on the seas.
- Petrol engines alone account for 70% of Benzine in the atomosphere in Europe
- Indoor Air pollution (smoke from central heating) kills 1,600000 (1.6 million) people WW


Looking at the dizzying array of deaths vs alleged (as every report has one agenda or another it seems) pollutant, who dares drive their petrol car and look with disgust on those driving burning other fossil fuels?

Or maybe look at the amount of people dieing from their home fires, which are not only killing them, but killing their neighbours too. No matter how much dirtier you think diesel is, its SMALL FRY compared to the bigger killers. The common factor here is fossil fuels. Petrol and Diesel are both very bad things, they are both killing me, you, the plants, the planet etc, no matter which way you break down percentages, so give it a rest or take it to to Green forum.

JHMEG

5. Does diesel exhaust cause cancer?

According to the Health Assessment Document prepared by the EPA and corroborated by the International Agency for Research on Cancer, the National Institute for Occupational Safety and Heath and the World Health Organization, diesel exhaust inhaled into the lungs likely causes cancer in humans. In urban areas, diesel exhaust may contribute as much as 70 percent of the cancer risk from toxic air pollution, which would make diesel emissions more harmful than all other toxic air contaminants combined (5).

Source (US Govt)

PaulKK

E92 wrote: »

+1
The diesel wiped the floor performance wise. It wasn't even funny how much faster it was, no need to drop down gears or anything like that, just press the loud pedal down more and it was well able to move.

.....

the diesel at only 1,600 rpm was full of enthusiasm and had no difficulty getting up to speed when this was done.

...........................................

The problem with the petrol wasn't the engine: it was with the driver. It's much more fun having to get a petrol in the upper half of the rev counter and hearing the engine work hard:D!

You have just given the best argument for diesel in this thread. Who in their right mind is going to rev their engine up near the redline every time they drive it?

Why would you thrash your engine like that in normal driving?

This is where diesel is superior, goes about its business quietly and without much fuss, delivering its power low in the rev range. Safer for overtaking for 90% of normal drivers.

Most people are not willing to rev their engines high, and quite rightly too, they're going to be wasting petrol and creating lots of unnecessary noise, apart from the fact that if your constantly thrashing it like that you'll need to service it a more often.


At the end of the day, your not in Mondello, your on a public road.

Matt Simis

You have just proved my point about the WHO research you quote verbatim, ad nauseum, let me edit your post to highlight something:

JHMEG wrote: »

5. Does diesel exhaust cause cancer?

According to the Health Assessment Document prepared by the EPA and corroborated by the International Agency for Research on Cancer, the National Institute for Occupational Safety and Heath and the World Health Organization, diesel exhaust inhaled into the lungs LIKELY causes cancer in humans. In urban areas, diesel exhaust MAY contribute AS MUCH AS 70 percent of the cancer risk from toxic air pollution, which would make diesel {editted for clarity: assuming all previous unqualified statements are true} emissions more harmful than all other toxic air contaminants combined (5).

Hmm, did someone say facts or conjecture?

JHMEG

That report is a little old. The actual variant of lung cancer was identified recently.

You are clutching at straws now Matt. If you want to keep putting yourself at risk and those around you, keep right on smoking diesel.

Matt Simis

JHMEG wrote: »

That report is a little old. The actual variant of lung cancer was identified recently.

You are clutching at straws now Matt. If you want to keep putting yourself at risk and those around you, keep right on smoking diesel.

Lol, priceless.

JHMEG

Matt Simis wrote: »

Lol, priceless.

You have my sympathies Matt. People refused to believe the earth wasn't flat in the beginning too..

Biro

craichoe wrote: »

Point taken, just twin turbo implies 2 turbos that are the same i.e. twins

Think of parallel layout as identical twins, and sequential layout as one girl twin and one boy twin turbo!

PaulKK

Matt Simis wrote: »

I drive BioDiesel

JHMEG wrote: »

You have my sympathies Matt. People refused to believe the earth wasn't flat in the beginning too..

Think you missed that bit

Cionád

JHMEG wrote: »

You are clutching at straws now Matt. If you want to keep putting yourself at risk and those around you, keep right on smoking diesel.

Thanks man, that gave me a laugh

Tails142

PaulKK wrote: »

Think you missed that bit

biodiesel produces just as much particulates as ordinary diesel. The only benefit of it is that when the plants grow they theoretically use up the CO2 that it will later emit when the oil is burned. Total crap in my opinion - I guess its ok for the people in the countryside though, just bad news for people in the cities.

craichoe

Biro wrote: »

Think of parallel layout as identical twins, and sequential layout as one girl twin and one boy twin turbo!

Thank god my g/f has twin boobs and not sequential boobs

E92

PaulKK wrote: »

You have just given the best argument for diesel in this thread. Who in their right mind is going to rev their engine up near the redline every time they drive it?

How often does one have to make an engine deliver it's maximum performance? If it's fairly often, then it's obvious that the engine is underpowered and shouldn't be in the car. Or else you're driving like a mad man and going as fast as possible even when it's completely unncessary.

And as for the argument about taking an engine to the redline, the chances are so rare on our roads that when they do turn up once in a blue moon won't damage the engine even slightly. Flooring an engine when it's not in it's powerband is the worst thing you can do to it. Dropping a gear or 2, getting the engine into it's powerband and only pressing the loud pedal a bit, and not only do you get a lot more excitement, but you're doing the engine a favour as is evident by how much better it responds to the acclerator. Flooring a diesel at low revs doesn't somehow not damage an engine "because the revs are low". Of course keeping an engine at or close to the rev limiter is going to affect the lifetime of the engine. But any responsible person changes up nice and early in normal driving, and when overtaking, drops down the gears, floors it, changes up at the rev limiter, and then once the manoever is complete, goes back into a much higher gear and eases off the throttle. Flooring an engine like that every now and again won't kill it. It's good for the engine to give it some stick every now and again. Changing up at the rev limiter when it's unnecessary and acting the eejit with an engine clearly is bad for it.

Revving a petrol engine high isn't that bad for it. Just look at the Honda S2000. It revs to 9,000 rpm and where does it finish in JD Power surveys? Exactly.

PaulKK wrote: »

Why would you thrash your engine like that in normal driving?

This is where diesel is superior, goes about its business quietly and without much fuss, delivering its power low in the rev range. Safer for overtaking for 90% of normal drivers.

Most people are not willing to rev their engines high, and quite rightly too, they're going to be wasting petrol and creating lots of unnecessary noise, apart from the fact that if your constantly thrashing it like that you'll need to service it a more often.

Modern turbo petrol engines deliver all their torque as low down in the rev range as a diesel, but unlike the diesels they can keep delivering it all the way up as much as 4-5000 rpm. And yet you can still floor them and take them to the redline just as you can with an NA petrol. Almost every manufacturer is in the process of turbocharging petrol engines these days. Turbos with direct injection is the future for the petrol engine.

Petrols have much shorter gearing so you inevitably do much higher revs at any given speed than a diesel. You don't exactly hear of petrols breaking down all the time because they spend most of their working life at much higher engine speeds than diesel.

Try going down a hill in a low gear at high revs in a petrol fitted with an instantaenous fuel consumption meter and you will find that actually the mpg is unchanged. It reads 99 in my car at 1,500 rpm and at 5,500 rpm in that situation. When you don't have your foot on the acclerator the engine uses practically no fuel. Believe it or not engines use more fuel in when coasting instead of using engine braking in those situations:p!

That makes your point completely null and void IMO.

E92

Tails142 wrote: »

biodiesel produces just as much particulates as ordinary diesel. The only benefit of it is that when the plants grow they theoretically use up the CO2 that it will later emit when the oil is burned. Total crap in my opinion - I guess its ok for the people in the countryside though, just bad news for people in the cities.

Never knew that - so JHMEG was right when he said "If you want to keep putting yourself at risk and those around you, keep right on smoking diesel" after all.

And the agument about how many people are killed by diesel fumes and that we should do nothing about it because so "few" are affected is complete bull**** - 336 people died on our roads last year, should we not try and improve road safety and cut the number of road deaths because 336 people in a population of 4 million is let me see....0.0084% of the country's population either:rolleyes:?

Can we now get back to which offers better performance, that's where this all started after all:)?

maidhc

E92 wrote: »

How often does one have to make an engine deliver it's maximum performance? If it's fairly often, then it's obvious that the engine is underpowered and shouldn't be in the car. Or else you're driving like a mad man and going as fast as possible even when it's completely unncessary.

That isn't the point. The point is you don't need to in a diesel. You can overtake without needing to drop a gear, which if nothing else saves a second or two from the manouvre and possibly saves the lives lost from the evil particulates that worry JHMEG so much.

E92 wrote: »

Try going down a hill in a low gear at high revs in a petrol fitted with an instantaenous fuel consumption meter and you will find that actually the mpg is unchanged. It reads 99 in my car at 1,500 rpm and at 5,500 rpm in that situation. When you don't have your foot on the acclerator the engine uses practically no fuel. Believe it or not engines use more fuel in when coasting instead of using engine braking in those situations:p!

That makes your point completely null and void IMO.

You missed the bit in Toyotas instruction manual which says the fuel consumption computer is inaccurate when going down a hill without throttle! It does say it!

This talk about particualtes is rubbish. As Matt said, it is small fry, and anyone driving a car that uses fossil fuels and does not have zero emissions (and that isnt a hybrid) is in no position to lecture anyone!

By the way the Avensis diesel pulls strongly all the ways to 5000rpm! In fact it is a much more petrol like diesel than anything from VW...e.g. it doesn't really have a wall of torque at 1600rpm -3000rpm and then fall away.

E92

BrianD3 wrote: »

Facts are hard to come by in this debate. Would you argue that cigarette smoke DOESN'T cause cancer? Because many regard that as a "fact" too.

A combination of flawed scientific research, poor knowledge/use of statistics, vested interests, people with agendas, media manipulation makes it hard to know what to believe.

I was just reading the other day that Grapefruits cause cancer in women. Is that a fact? The Irish Independent thought it factual enough to publish it in their health supplement

PS i am not suggesting that you are wrong about diesel exhaust containing high levels of particulates and NOx. These can be easily measured. However the actual effect of diesel exhaust on a human population is much harder to determine.

Your point is very valid. We're all gullible here. No matter what side of any argument you are on, you will always try and find something/someone respected that agrees with your beliefs. If you're in favour of anything or against anything, it's very hard to be objective about it.

The medical people say that PM and NOx causes cancer though. I'm no expert in that area, but that's what they say, and I know that diesels are allowed by the EU to be far worse than petrols for these emissions. I'd like to think the WHO wouldn't be saying that diesel fumes cause cancer if it wasn't true:).