It's called Automation, and although it's beta, it seems to be fairly polished. The basic premise is that you run your own car company, but with the added twist that you can also design your own car from the ground up. Yes, that means you can even design your engine.
There's a demo available for those of us who are too poor due to Christmas to afford the $25 to purchase the full version. It only gives you limited options, with the I4 being the only engine build choice. The best I could do was 381hp at 7800 rpm, so I would really, really like to see what could be done with better engine options.