Poll: 1.0L Mirage engine = 7.5% better fuel economy. Would you choose it?

[owl]

Yes! I like to drive 180km/h most of the time. Having to slow down to 172km/h would make it feel like I was crawling - you know how it is, watching the pavement slowly pass underfoot thinking "I might as well just get out and walk!"

Also, sometimes instead of brushing the snow off my car I just wind it up to around 178km/h to blow the snow off, and it seems that the 1.0L engine would not be capable of this, so it means more work ....

That's why we need turbos. That opaque ice on the windshield usually doesn't start peeling off until after 182 km/hr. As for 172 km/hr....well....life is just too short to be spent dawdling with the crawling, molasses inspired masses.

[owl]

[/QUOTE]For those of you who got the 1.2, would you have bought or considered the 1.0 if it were available? You get a bit less power, but better fuel economy?[/QUOTE]

I am not convinced about the fuel consumption numbers. It seems to me that the number of cylinders a motor has is more important than displacement...all other things being equal. The fewer the cylinders, the less internal friction, the less fuel burned just turning the engine over.

When you have two identical cars going the same speed down the road, they have to produce the same horsepower to overcome rolling resistance and wind drag

Same output power will mean same specific fuel consumption. The smaller engine will obviously be working a bit harder to produce that power. That means its fuel consumption will rise to that of the bigger engine.

My proof for this theory is a test of two two cylinder motorcycles last summer. A friend has a 96 cubic inch Harley Dyna. I, obviously of more refined character, have a BMW R60/7..which is 600 cc. (Roughly 37 cu.in.). Neither bike has a fairing.

We both filled up and did a 200km cruise at about 100 km/hr. We filled up again and found that the Harley used only one quarter of one Litre more gas.

In summation, any identical three cylinder cars going the same speed, on the same road, with the same cargo and tire pressure will be so close in fuel consumption as to be statistically identical.

I feel any better fuel consumption by the smaller engine Mirage is likely due to the greater frugality/thrift of their owners as compared to those pompous, extravagant, extroverted, peacock feather wearing, self important braggarts who have the 1.2L engined variety.

[Daox]

Same output power will mean same specific fuel consumption. The smaller engine will obviously be working a bit harder to produce that power. That means its fuel consumption will rise to that of the bigger engine.

Sorry to burst your bubble, but that is not how it works. Its a very common misconception though.

Engines in general love working hard. They give you more power for less fuel when pushed hard. When pushed extremely hard (into open loop and fuel enrichment at high rpms and high engine load) the efficiency drops, but still not horribly.

Here is the proof, a brake specific fuel consumption map for a 1.4L turbo VW engine. The vertical is engine load, the horizontal is rpm. The map shows fuel use per amount of power output. This map looks quite similar for many different engines. We have compiled a list of them on another website we run here:

Brake Specific Fuel Consumption Maps



There are many reasons that engines like being worked hard, but the main one is what is called pumping losses. It takes power to spin an engine, push valves, suck air in through a mostly closed throttle, etc. If you open that throttle up, it gets a LOT easier for that engine to spin over because its not fighting the vacuum. There are multiple other reasons that engines love being loaded up, but that is the main one.

So, if you take two engines and one is a bit smaller than the other. You look at that graph, the smaller one is going to be working harder (higher up on the chart) to put out the same amount of power. That means its going to be operating more efficiently.

[owl]

Sorry to burst your bubble, but that is not how it works. Its a very common misconception though.

Engines in general love working hard. They give you more power for less fuel when pushed hard. When pushed extremely hard (into open loop and fuel enrichment at high rpms and high engine load) the efficiency drops, but still not horribly.

Here is the proof, a brake specific fuel consumption map for a 1.4L turbo VW engine. The vertical is engine load, the horizontal is rpm. The map shows fuel use per amount of power output. This map looks quite similar for many different engines. We have compiled a list of them on another website we run here:

Brake Specific Fuel Consumption Maps



There are many reasons that engines like being worked hard, but the main one is what is called pumping losses. It takes power to spin an engine, push valves, suck air in through a mostly closed throttle, etc. If you open that throttle up, it gets a LOT easier for that engine to spin over because its not fighting the vacuum. There are multiple other reasons that engines love being loaded up, but that is the main one.

So, if you take two engines and one is a bit smaller than the other. You look at that graph, the smaller one is going to be working harder (higher up on the chart) to put out the same amount of power. That means its going to be operating more efficiently.

Comparing a turbo to a normally aspirated engine is like the apples and oranges scenario. You at least agree that the smaller engine has to work harder for a given load. The only way it can possibly work harder is to burn more fuel/air. That can be done by wider throttle opening or increased rpm (or both). Either of which causes an increase in fuel consumption.

Remember also, the increase in internal engine loading/friction goes up as the square of the rpm. That causes fuel usage increase also.

Your turbo comparison is flawed, because as the rpm of the turbo increases, the more the motor is tricked into thinking it's displacement is much greater than it really is. You can get big increases of boost at much lower engine rpm...depending how much exhaust gas your gas pedal dictates. Not to be confused with Supercharging, which is almost one hundred percent rpm based boost.

Anyway, I certainly don't feel as though I'm labouring under any grossly distorted sense of reality. Heck...not even a misconception..

[owl]

Sorry to burst your bubble, but that is not how it works. Its a very common misconception though.

Engines in general love working hard. They give you more power for less fuel when pushed hard. When pushed extremely hard (into open loop and fuel enrichment at high rpms and high engine load) the efficiency drops, but still not horribly.

Here is the proof, a brake specific fuel consumption map for a 1.4L turbo VW engine. The vertical is engine load, the horizontal is rpm. The map shows fuel use per amount of power output. This map looks quite similar for many different engines. We have compiled a list of them on another website we run here:

Brake Specific Fuel Consumption Maps



There are many reasons that engines like being worked hard, but the main one is what is called pumping losses. It takes power to spin an engine, push valves, suck air in through a mostly closed throttle, etc. If you open that throttle up, it gets a LOT easier for that engine to spin over because its not fighting the vacuum. There are multiple other reasons that engines love being loaded up, but that is the main one.

So, if you take two engines and one is a bit smaller than the other. You look at that graph, the smaller one is going to be working harder (higher up on the chart) to put out the same amount of power. That means its going to be operating more efficiently.

Comparing a turbo to a normally aspirated engine is like the apples and oranges scenario. You at least agree that the smaller engine has to work harder for a given load. The only way it can possibly work harder is to burn more fuel/air. That can be done by wider throttle opening or increased rpm (or both). Either of which causes an increase in fuel consumption.

Remember also, the increase in internal engine loading/friction goes up as the square of the rpm. That causes fuel usage increase also.

Your turbo comparison is flawed, because as the rpm of the turbo increases, the more the motor is tricked into thinking it's displacement is much greater than it really is. You can get big increases of boost at much lower engine rpm...depending how much exhaust gas your gas pedal dictates. Not to be confused with Supercharging, which is almost one hundred percent rpm based boost.

Anyway, I certainly don't feel as though I'm labouring under any grossly distorted sense of reality. Heck...not even a misconception..

[Daox]

As I said, they're all quite similar maps. We even have a bunch of diesel ones and they all look very similar.

Here is a 2.0L Zetec Ford engine.





Here is a 1.9L Saturn engine.





Here is a 3.0L Toyota V6 engine.





Here is an 09 2.0L VW TDI engine.





They all look pretty similar. They all say engines are more efficient at higher loads. This is why smaller engines are more efficient. These charts take into account internal friction and everything else engine related as they're done on a dyno. I'm not trying to be a jerk or anything, but this is well established science.

[deleted user]

Smaller engine, higher load= higher efficiency

More air in cylinder of the smaller engine means higher real compression, which produces more power with less air fuel mixture.

The harder the engine has to work the lower the restriction to incoming air, more air in cylinder.

The smaller engine running at the same speed, with identical manifold vacuum (inverse of map) uses 20% less air fuel mixture.

Example 2.5 liter engine on a dyno producing 20hp uses 1x amount of fuel. Increasing the load to 50 hp uses 1.5x fuel, with the extra 50% fuel producing an extra 30 hp.

20/1 = 20 hp per unit of fuel
50/1.5 = 33.33 hp per unit of fuel

The higher the actual (in the cylinder) compression the greater the power produced ON THE SAME AMOUNT OF FUEL.

Think about it, the engine is basically a lever. The more air fuel mix you put in the cylinder the greater the efficiency of the engine, AS LONG AS THE FUEL MIXTURE IS NOT SUBJECT TO ENRICHMENT.

regards
mech

[owl]

Smaller engine, higher load= higher efficiency

More air in cylinder of the smaller engine means higher real compression, which produces more power with less air fuel mixture.

The harder the engine has to work the lower the restriction to incoming air, more air in cylinder.

The smaller engine running at the same speed, with identical manifold vacuum (inverse of map) uses 20% less air fuel mixture.

Example 2.5 liter engine on a dyno producing 20hp uses 1x amount of fuel. Increasing the load to 50 hp uses 1.5x fuel, with the extra 50% fuel producing an extra 30 hp.

20/1 = 20 hp per unit of fuel
50/1.5 = 33.33 hp per unit of fuel

The higher the actual (in the cylinder) compression the greater the power produced ON THE SAME AMOUNT OF FUEL.

Think about it, the engine is basically a lever. The more air fuel mix you put in the cylinder the greater the efficiency of the engine, AS LONG AS THE FUEL MIXTURE IS NOT SUBJECT TO ENRICHMENT.

regards
mech

I don't know where you guys are getting your ideas of small = efficient. It simply is not true. The biggest single problem in engine design is keeping the combustion heat from being sucked away into the cylinder walls and the head. You want that heat doing work, not going into the environment. Increasing the cylinder bore size is one way of doing that.

If you double the bore of a cylinder, you increase the volume by a factor of eight but the surface area only goes up by four. Less heat loss = more efficiency.

Don't believe it? Check out the efficiency of those ocean going diesels. They are getting 50 percent efficiency. If they could save even a few percent of fuel consumption by using more, smaller engines they would have done it fifty years ago.

In internal combustion engines, the larger you can make the bore, with the least number of cylinders possible for the application the more power you will get for a unit of fuel.

Come on people, this is first year thermodynamics. Go do some homework

[owl]

That should have read

4 times the volume
But only
2 times the area

'Rithmetic...I missed the day they did volumes..

[deleted user]

I don't know where you guys are getting your ideas of small = efficient. It simply is not true. The biggest single problem in engine design is keeping the combustion heat from being sucked away into the cylinder walls and the head. You want that heat doing work, not going into the environment. Increasing the cylinder bore size is one way of doing that.

If you double the bore of a cylinder, you increase the volume by a factor of eight but the surface area only goes up by four. Less heat loss = more efficiency.

Don't believe it? Check out the efficiency of those ocean going diesels. They are getting 50 percent efficiency. If they could save even a few percent of fuel consumption by using more, smaller engines they would have done it fifty years ago.

In internal combustion engines, the larger you can make the bore, with the least number of cylinders possible for the application the more power you will get for a unit of fuel.

Come on people, this is first year thermodynamics. Go do some homework

Maybe second year might help you.

regards
mech