Can a V8 fit in Pontiac Sunfire?

No, a V8 engine will not fit in a Pontiac Sunfire. The Sunfire was a compact car designed for smaller, more fuel-efficient engines. The engine bay is simply too small to accommodate the size and width of a V8 engine, even with significant modifications. While some extensive custom fabrication *might* be theoretically possible, it would be an incredibly impractical and expensive undertaking, not to mention likely compromising the structural integrity of the car.