I think it's an engine when you can modify it. If you're working on a car you can make it faster in the 1/4 mile or you can make it get better fuel economy. You can adjust it so it works well at high altitudes or in a dusty desert rally. An engine should already be capable of driving somewhere in one way ... and it should allow you to modify it to drive anywhere.
Blitz3D is a bunch of nuts, bolts, and assorted parts which you can form into an engine ... but it doesn't do anything without some assembly. Torque on the other hand already does the FPS game ... when you download it you can immediately play a game and then if you want you can immediately pop the hood and start adding the 'cold air iduction' and 'high flow mufflers', etc...
Blitz3D is a bunch of nuts, bolts, and assorted parts which you can form into an engine ... but it doesn't do anything without some assembly. Torque on the other hand already does the FPS game ... when you download it you can immediately play a game and then if you want you can immediately pop the hood and start adding the 'cold air iduction' and 'high flow mufflers', etc...