I’m a rare bird, indeed.

I’m quick - for my time - in my own right but I’m deeply overshadowed by my big brother, who is a full-on muscle car. I’m powered by an advanced-for-the-time engine that overpowered some of its bigger rivals while delivering economy-car fuel mileage. The car magazines of the time loved me, and enthusiasts liked my (for the time) high-revving, well-balanced inline six, but the US market wasn’t ready for me yet.

Because I was several years ahead of my time, I ended up a sales flop.

Who am I?

Edit: RamblinRover wins one internet!