Does Engine size and gear ratio REALLY matter?

[cosmick]

Originally Posted by P-hack

The smaller engine is more likely to come with a smaller/lighter car.

Amen!

[Arragonis]

Hmm mm. Turbos. Go debate.

[rmay635703]

Originally Posted by NoD~

Now, to be perfectly clear: This is a theoretical, on paper idea. I realize that there's a billion other variables to this equation.

That said, the thought process here is, in real world ideology, to compare in regards to the idea of, say, an engine swap to a different engine or changing out transmission for different gear ratios, all while still using the rest of the car. Even then, there's obviously variables...
.

Plain and simple a smaller engine will always get better fuel economy if it is of equal efficiency as compared to a larger one.

Unless the small motor has terrible gears and poor fuel delivery there is just no comparison.

That is why the mother earth 40mpg full size trucks do so with their 5hp - 25hp engines.

Obviously drivability is removed but fuel economy is great.

This is of coarse removing P&G and obviously removing what happens if the motor is so small that you run it at redline to maintain 55mph

[some_other_dave]

Originally Posted by cosmick

I can find you 1.1L cars that never could do 30 MPG, and I can find you 6.0L cars, with more drag, that can return 35 MPG consistently, no mods to either.

Of course you can--there are enough tradeoffs that you can find just about anything if you look hard enough. Especially if you're looking for lower economy numbers. (Heck, just leave the handbrake on and you'll find lower economy numbers!!)

That doesn't mean that the larger engines get the same economy as the smaller ones.

-soD

[Occasionally6]

Originally Posted by rmay635703

Plain and simple a smaller engine will always get better fuel economy if it is of equal efficiency as compared to a larger one.

Unless the small motor has terrible gears and poor fuel delivery there is just no comparison.

That is why the mother earth 40mpg full size trucks do so with their 5hp - 25hp engines.

Obviously drivability is removed but fuel economy is great.

This is of coarse removing P&G and obviously removing what happens if the motor is so small that you run it at redline to maintain 55mph

Pick a power requirement i.e. a particular rate of acceleration or road speed for a vehicle. For the sake of this we'll assume a CVT and that the engine can operate at a single - ideal - load and speed.There is a "right size" for the engine that will provide that power with the greatest efficiency. Both larger and smaller engines will be less efficient, just on different sides of the peak of the BSFC island.

From the OP:

Originally Posted by NoD~

Lets say you have a 1.0L engine VS a 2.0L engine. They both use the same technologies, such as fuel injection, cam specs, etc. ..... Efficiency is just about even on these engines....

...Here's my thoughts on it: If they both consume an equal amount of fuel to produce an equal amount of power and things like idling is thrown out of the equation, should engine size actually matter? And with gearing: As long as you stay in the appropriate RPM range (such as referenced to a BSFC), is there really any point in gearing changes as long as you don't cruise in a set gear?

If they scale perfectly they won't produce the same power with equal efficiency across the whole speed and load range. If you are going to pulse and glide they could be equally efficient with the acceleration rates proportional to engine size.