The first generation of the BMW X3 may have sold well, but it wasn't one of the brand's top accomplishments: the 'Bangled' design was controversial, interior quality lagged far behind the X5 of the time, it couldn't go off-road, and on-road, it drove rather harshly. So, how do you go about improving it? Well, how about replacing the original motor with one of BMW's most iconic straight-six engines?

That's exactly what a brave owner did. In a Facebook group called EastCoast BMW Classifieds, Corey Dalba posted an ad of his X3 which has been fitted with the 3.2-liter S54B32 engine from the E46 M3. Between 2001 and 2006, this engine ruled the International Engine Of The Year awards in the 3.0-liter to 4.0-liter category.

Although its outputs of 338 horsepower and 262 lb-ft of torque sound rather puny today, the naturally aspirated S54's wail as it soared to its 8,000 rpm redline is legendary. It contributed to the E46 M3 being one of BMW's most memorable cars ever before the sports coupe morphed into the heavier M4 we have today. Whether a 15-year-old X3 is our first choice for an S54 heart transplant is debatable, but we can only imagine how rapid this SUV is. According to the ad, everything works and Dalba uses the M/X3 as his daily driver.

It has a new clutch, a new transfer case, a fresh headliner, and "everything is coded properly and works like it was from the factory." He further goes on to say that "I would trust this vehicle to take me anywhere, and have for the last two years." The mere sight of that M classic in the engine bay is enough to convince us, and even the personalized license plate cheekily states "MPROVED". Admirably, Dalba managed to resist affixing a hoard of M badges to the exterior, turning this into the ultimate sleeper SUV. Or, put another way, the spiritual predecessor to today's X3 M.

As part of the upgrade, the all-wheel-drive layout was maintained and the X3 also received new springs, sitting slightly lower than the stock model. Most commenters seemed suitably impressed, especially after Dalba later posted a video of the X3's instrument panel while flooring it - hilariously, the S54 continues its rise up the rev range long after the X3's tachometer needle reaches its 7,000 rpm maximum. What's undeniable is that the engine note is exactly as we remember and makes a mockery of the latest M3's synthetic acoustics.

According to another comment on the seller's ad, Dalba has been struggling to sell the M3-engined X3 and this will be his last attempt. If he doesn't convince anyone to buy it, he'll be heading back to his workshop and using the S54 in one of his e30s. Now THAT would be something…

For now, the most desirable first-gen BMW X3 in America is up for grabs.