"Research Vehicles" questions
 

Where do all the engine choices come from? Why are there so many more choices than actual engine options for specific models?

Sounds like they have subscriptions for the data. Covering multiple markets can mean more engine options in total, or some choices are duplicated as the databases are combined.

Trollbait nailed it.

Even with all of the engine options, there are many that are missed.

I notice also besides what must be duplicate engines there are duplicate models like in Hyundai Sonata there is the Limited 2.0T (23) and 2.0T Limited (35). There is also Ultimate 2.0T (10) which is identical running gear with a few other non-mpg options. Also in the Sonata there is GAS (41), H4 GAS (48), L2 GAS (11) and L4 GAS (257). Those, especially the first one, are of no use or value in determining accurate averages for anyone as they could be anything and would skew the results of the correctly identified 2.0 or 2.4 or whatever engines.

I may be all wet with the engine choices but it definitely affects averages when you have some cars in 2.0 X and others in X 2.0.