Quote:
Originally Posted by SPACEMANRICK
Yes it is all relative and a compromise........ gas mileage, power, sound, weight etc. The M3 sounds ferocious at full throttle but many M3 drivers are averaging 16 to 17 litres per 100 km, I am now averaging about 10.5 litres per 100 km in my 335 xdrive and I assume many 328 drivers are averaging about 8 to 9 litres per 100 km.
|
If you're comparing 335xi to 328i RWD, then that may be true.
But we have to have more data to see real world MPG differences.
The RWD versions haven't been showing a big difference.
MPG does favor the 328i but only slightly.
Remember, comparing equally optioned cars the weight difference isn't that much, somewhere around 120lbs.
The MPG differences will be greater only when either car is driven hard using maximum power output.
The N55 will use more fuel as it will also produce more power when called upon by the drivers throttle foot.
Driven at a good bit less than maximum, which is how most drive on a daily basis, either engine will need to put out around the same hp/torque.
When doing that either engine will need and use close to the same amount of fuel. With that manner of driving the MPG difference will be more about the 328i's slightly lower weight, and potentially less friction loss as the N20 has 2 fewer cylinders.
The great equalizer here is that both cars use the same trans with the same gearing and same final driver, along with same diameter wheels/tires.
So if a 335i is driven hard and fast with the driver calling up near max power for for extended miles, and a 328i driver is doing the same, that's where the 335i's N55 will use more fuel.
But how often is the case except on the track.
I mentioned earlier that there is a potential that the 4cyl N20 may have lower frictional losses in the engine. I don't have any data or information that that is true or not true. Speculation is that there is less in the N20, but I doubt it's a lot, but even a bit less will give higher MPG over time and miles.
Lower frictional loss pay back higher dividends in better MPG especially on longer highway drives. In those conditions it takes less hp/torque to keep the vehicle at speed vs accelerating. Of course this would be for normal and nominal high speeds where it doesn't take a lot of power to keep the car moving at a stead rate.
At highway driving, the N20 should have an advantage if there is less friction loss. But that potential could be mitigated by the N20's added friction due to the balance shaft assembly. So it's an interesting question as to which engine has greater internal friction losses.
You have the N20 with 2 less cylinders, but it also has balance shaft assembly.
The N55 has 2 more cylinders, and total ring surface area is greater adding to it's friction level.
The F30 is great setup by which to see MPG differences attributed mostly to engine size and cylinder count.
The reasons being that equally equipped there is not a big difference in actual on road vehicle weight, with the 335i weighing only about 3.7% more.
And, with an AT they have the same identical trans, so gearing is taken out of the equation.
They even use the same wheel/tire size, and in some cases the same tires.
There is a stock tire pressure difference iirc, due to the weight balance difference.