95 versus 99 octane petrol

speakerguy79 said:

The gas mileage isn't great, but it's not as terrible as you'd think it would be. The 4.6L will get 22mpg on the highway. Fortunately I live but 1.7 miles from my work.

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That isn't really great compared with the max. allowed speeds (~90kmh) in the USA. Roughly 22mpg corresponds to 11.5liters per 100km.

Driving e.g. the Ford Mondeo at an average speed of 120kmh (~75mph) it takes about 8l per 100km.

Conclusion: Big engines are just fuel wasters.

Boncuk

I agree they waste fuel, but they're also a lot more fun Damn, the things I could do in my old 1989 Crown Vic with a 5.0L V8 would blow your mind. That was my first car I inherited from my grandmother. It was an old lady's car save for the fact it had the same V8 the Ford Mustang at the time had (albeit tuned differently). I went through a lot of rear tires in high school with that old beast.

for some reason americans are obsessed with size ! I own the MK2 mondeo this was made larger than the MK1 because..... it was not selling in america, I'm not complaining about the size though, I would not have chosen something so big but as it was going cheap and is in great nick took it on. it is 150 Kg lighter than my dads 1.4 L escort (which is a smaller car btw) so yes ! 1.8 L is large in this perspective, the car is quite capable of reaching 70 mph with is the maximum speed limit in the UK and its as fast as I would be comfortable going.

I see no point in a bigger engine its just a liability costwise to start with, I think i have the best compromise for performance vesus economy and Im quite happy.

DOHC also allows the valves to be angled to improve airflow.

Higher octane fuel burns slower. That can reduce the power and economy. Obviously, knocking needs to be avoided, and higher octane fuel is more resistant to knocking, allowing higher compression ratios, so some cars are designed for higher octane fuel.

Most cars now adjust the timing to avoid knocking, but the algorithms for that vary in how well they work, so some cars may well be smoother on higher octane fuel.

At high engine speeds, the slower burning of higher octane fuel means that the cylinder pressure doesn't rise as fast, so the piston can be well on its way down before peak pressure is reached.

Just a question - where do you get 99 octane fuel from?

Boncuk said:

Not quite.

DOCHs make the pushrods and leverage for valve operation unnecessary saving power.

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Sorry, but quite

We're talking DOHC here, you're comparing it to 1950's pushrod engines - I was comparing it to SOHC which is the alternative on lower performance cars.

I would presume a DOHC actually uses MORE power opening the valves, as there are twice as many, and as it's intended for higher revs they use stronger springs.

But as you say, Americans seem obsessed by massive cars and silly size engines - yet they don't have the same performance as much smaller European engines.

I drive a Fiat Punto, 1.2L 8V - does about 45 miles per gallon, cheap to run and plenty fast enough with modern speed limits. Probably reaches just over 100mph?, and 70mph (motorway speed limit) at 3000 revs in 5th.

I'll throw in a grenade here.......



Drive a diesel....much more economical...even if it costs 1 -2p per litre more...

I drive a 2006 Ford Mondeo Diesel Estate with the 2 litre twin cam turbo charged engine...returns around 50 mpg on a decent run and runs 2000rpm in 6th gear at 80mph....

on a run I'd probably get better than that, my book says 56 mpg and I always tear those figures to shreds

I wish we could get those cars here!

The "gas crisis" last year put a nail in the coffin of the SUV. Several people have said the Americans have an obsession with large engines and wastefulness... I think the tide is shifting, huge vehicles are on their way out.

I drive 135km (85 miles) everyday and have what is considered a small engine here (2.4L sohc Dodge Stratus avg 30mpg). I choose to live out in the country away from the city and have to pay the commuter piper. Love my job but love my house more.

I'll just throw in a slightly different perspective. Here in Australia people drive larger distances than most other countries. There is also the fact that if you break down in the outback then you will probably die. So, people choose large engined cars and so the rest of the world sees Australia as a wasteful country. However, when I was in the UK a car that had done 100k was a scrapper, a complete rust bucket with a worn out engine. Here a car is expected to do at least 250k and probably 500k. They can do this because they have large but lowly tuned engines. The 1.8L UK cars have the same power as the 3L cars here but they are worn out in 100k (probably less). Anyone that flies planes understands this, aircraft engines rev to 2500 revs because that gives reliability.

End of the day, to propel a vehicle takes X energy, more weight more X, size of engine is irrelevant. Two cars that weigh the same will use the same amount of fuel regardless of engine size. The only down size is the engine weighs more and so the vehicle uses more fuel. Upside is it last 4 times longer.

Makes you think doesn't it. Big is not always better or badder.

Mike.
FYI, I have a 5L ford and a 5.8L Land Cruiser. But, the kids have smaller cars.

Pommie said:

I'll just throw in a slightly different perspective. Here in Australia people drive larger distances than most other countries. There is also the fact that if you break down in the outback then you will probably die. So, people choose large engined cars and so the rest of the world sees Australia as a wasteful country. However, when I was in the UK a car that had done 100k was a scrapper, a complete rust bucket with a worn out engine.D

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Cars rust in the UK because of the climate, nothing to do with engine size

More modern cars are generally far better though, with galvanised steel been used - but in the past some makes of car were absolutely terrible for rust, particularly Italian ones. Salt on the roads in winter is the big bodywork killer.

Even small engines do pretty high mileage's here as well, engines aren't knackered at 100K - unless you seriously abuse them. But even if a small engine only lased 100K, the original cost of the engine, the much greater quantity of fuel used, and the higher servicing costs, means the smaller engine is far more cost effective.

But if you want long engine life go for a diesel, and get the good mileage as well. Ideal for the long distances you talk about, but I do agree a large petrol engine would be better than a small petrol one for long distances.

Do you agree that weight rather than engine size defines millage?

Mike.

Pommie said:

Do you agree that weight rather than engine size defines millage?

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Both really - the bigger the engine the more fuel it will use, and also the heavier the vehicle the more fuel it will use. What you don't want, is a heavy vehicle and a small engine.

I don't know if you watch F1?, but every litre of fuel in the tank costs about 1/10 second per lap.

Bigger engines only use more fuel if they produce more power. Two cars that weigh the same will use the same amount of fuel regardless of engine size. Big or small they produce the same amount of power per liter of fuel. End of the day it is just energy.

The UK got into this small engine stuff because the insurance companies decided that 1.8 liter was a big engine. The motor companies responded with tuned up 1.8L engines that produced the same power as a "non UK" 3L engine. Net result, UK engines wear out much quicker.

When I first arrived here I was amazed at the size of the engines in cars but then I drove a few and found that they produced half the power of a UK equivalent. It took many years to see that the folly was caused by the UK insurance companies.

Mike.

Pommie said:

Bigger engines only use more fuel if they produce more power. Two cars that weigh the same will use the same amount of fuel regardless of engine size. Big or small they produce the same amount of power per liter of fuel. End of the day it is just energy.

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Bigger engines weigh a great deal more - so use more fuel. Check fuel consumptions of identical cars with different engine sizes - the larger engines almost always use more. They have been, and may still be?, a few exceptions - the original 850cc Mini's weren't as good on fuel as the 1000cc ones, but 850cc was really too small.

The UK got into this small engine stuff because the insurance companies decided that 1.8 liter was a big engine. The motor companies responded with tuned up 1.8L engines that produced the same power as a "non UK" 3L engine. Net result, UK engines wear out much quicker.

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The UK don't have special engines, they are the same as anywhere else in Europe, and I don't think Japanese imports have special ones either? (certainly plenty of people import replacement Japanese engines direct from Japan).

well my thinking was somewhat along the lines of wht pommie said, bigger engine will no neccesarily mean more fuel consumption, ok my old 1 L atoz probaly weighed 800 Kg or less, my mondeo 1375 Kg so yes I will use more fuel to move this extra weight but its probably using less pertrol per Kg than the atoz. the atoz engine used to run very fast, so infact a 1 L engine was undersized and to make up it was run faster, the mondeo runs much more slowly so I think is more efficient (less engine friction), at 50 mph it does about 2000 rpm but I'm pretty sure the atoz ideled at that ! and must have run at about 4000 rpm to have any power at all it was very unforgiving of improper gear usage, I can climb a hill at 30 mph in 4th gear with the mondeo.

the engine in a container ship runs at juast 102 rpm and is up to 50 % efficient, that a lot more than the 30 % of a car engine, why ? because ot goes so much more slowly !

Engine speed doesn't equate to efficiency - just to the specific design of the engine - speed of a container ship engines is down to size.

Some cars are high reving, some are low, both can be quite fuel efficient. We had a Volkswagen Golf at work, I couldn't believe how high reving it was, took lot's of right foot to set off.

Pommie said:

End of the day, to propel a vehicle takes X energy, more weight more X, size of engine is irrelevant. Two cars that weigh the same will use the same amount of fuel regardless of engine size

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When I lived in South Africa, a Vauxhall Viva ( which was a current model in the UK at the same time) had less power than its UK counterpart purely because of atmospheric conditions....Being higher above sea level than the UK the air was thinner, ergo the power output of the engine was lower....I was even more surpried when I bought a Chevrolet 2500 ( I think it was the equiv of the Opel Commodore ) on how poor the performance was for a 2.5 litre powered car........

I think basically the atoz engine design is crap !

Chippie said:

When I lived in South Africa, a Vauxhall Viva ( which was a current model in the UK at the same time) had less power than its UK counterpart purely because of atmospheric conditions....Being higher above sea level than the UK the air was thinner, ergo the power output of the engine was lower

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You needed a turbo on it

Vauxhall Viva with a turbo, pretty cool!.