yes thats the one, apparantly a powerful engine although I'm not into speed but I figure that a powerful engine will have more power at low revs and so I should recover fuel by being able to loose gears at lower speeds instead of having to change down more often, for example I have no trouble approaching the roundabout in 4th gear, dropping to 25 mph and then going round the corner and up the hill picking up speed quikly and getting to 5th gear more quickly

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DOHC's usually have more power at high revs, as it enables more air to enter the engine.

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right ok but being a big engine anyhow I figure it copes better at lower revs

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Wow, you guys in the UK call a 1.8L engine big? That's a large motorcycle engine over here in the states I've got a 5.3L V8 in the car I'm driving now, and had a 4.6L in the car that's in the shop. Both SOHC I think (maybe DOHC), but not particularly high-revving.

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.

 

Not quite.

DOCHs make the pushrods and leverage for valve operation unnecessary saving power. Valve opening and closing time generally depends on the steepness of the cam, hence controlling fuel/air amount. Omitting several mechanical elements increases the overall engine performance. Further the cam is adjusted to have direct contact with the valve pushrod via a small piston, thus eleminating the need for length compensation like pushrods require. Ford uses hydraulically driven self-adjusting cam drives.

Increasing just air results in a lean mixture, increasing cylinder head temperature - in extreme cases leading to engine fire, to be recognized by white smoke.

(Cylinder heads are usually made of aluminum/magnesium alloy.)

Boncuk

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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

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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.

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Never buy "Trust" products, all mine broke !!!

 

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.

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

 

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.

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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....

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

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Never buy "Trust" products, all mine broke !!!

 

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.