He has used strange platforms in the past, but those were all just tossing something WIP onto an existing platform as a test bed. GM for drivetrain, 800-Series for linelock. But there's no i5 in the public release of the game. Which means he went out of his way to use that sound for no apperent reason other than A) There's a WIP i5 B) He was just messing with us IMO they are equally likely options. Some new-ish European hatchbacks do use i5/VR6 engines, so if this new brand is European then it is a possibility.