Originally Posted By: d00df00d
Originally Posted By: rshunter
Comparing the fuel efficiency of two significantly different vehicles and allotting the difference, in its entirety, to the engine design is absurd at best.
I'm pretty sure that's exactly the point. I.e., you can't judge the inherent fuel economy of an engine type when most of the cars in which it is used have an inherently inefficient drivetrain type.
Hence, "AWD has nothing to do with the fuel economy of the
engine."
We're on the same page of the tech manual, but I'm apparently not getting
my point across. That is, some here aren't recognizing that the fuel economy numbers being used as a point of reference tell us
not about the fuel efficiency of the engine, but of the vehicle as a whole. Using the EPA numbers of an AWD car to conclude the opposed-piston engine is inefficient is simply without factual basis. But, that is precisely what is being done.
What is actually being seen is that an AWD car requires more energy to propel than a 2WD car. Thus, AWD has
everything to do with
this point of reference. You simply can't separate one from the other in
this situation. The original post by "mormit" was simply pointing out that the observed fuel economy numbers were influenced by the use of AWD. We've yet to see any substantiation of the earlier claim that the engine design is, itself, less fuel efficient.
As an example, compare the numbers for two otherwise identical compact trucks. The 4WD version will have EPA numbers that are a couple of MPG lower in both the city and highway ratings. Does this mean that the
exact same engine, in the 4WD version, is inferior to the one in the 2WD version? Anyone with a degree of sense realizes that the answer is
"NO". Yet this is just the type of comparison that is being used to purport an inefficiency of the opposed-piston design. Anyone with engine design experience knows that cylinder orientation has
"sod all" to do with BSFC numbers...