Dinan 550xi S2, the 200-mph M5 that BMW doesn’t build: Motoramic Drives

If you’ve ever owned a BMW, you’ve probably pined for some Dinan upgrades. The company, founded by Steve Dinan in 1979, occupies the sort of space that AMG once did for Mercedes, before it was brought in-house — while Dinan isn’t officially affiliated with BMW, the Germans clearly don’t hate what he’s doing. And what he’s doing is taking fast BMWs and making them faster.

Amidst the chaos of Pebble Beach, I get a chance to head out for a drive with Dinan in his 550xi S2, an all-wheel-drive 5-series with reworked suspension and brakes. And also more power; instead of the stock 550’s 400 hp, the Dinan car makes 508 horses and a staggering 584 lb-ft of torque. The speed limiter is jettisoned, giving the car a claimed top speed of more than 200 mph. How far away are the Bonneville Salt Flats, anyway?

Even with a turbocharged V-8, adding that much power involves more than an ECU reflash. Dinan hardware includes larger intercoolers, a new exhaust and a cleverly reworked intake. Where the stock 550 uses diagonal chassis braces at the front corners of the engine bay, Dinan installs hollow braces that act as a secondary pathway for air to enter the intake. He says the system increases flow by 20 percent.

I’m honestly not going to be able to test the suspension upgrades in the environs of Pebble Beach — 17-Mile Drive is a poor venue for seeking max g-forces — but I do get plenty of chances to dip into the throttle and feel that wave of torque at work. With all-wheel-drive, the 550xi S2 just lays down the power and crushes you back in the seat. It already feels, to me, much like what you’d expect out of an AWD M5. But if you want to get even closer to that ideal, you could opt for the S3. That one includes bigger turbos and makes 542 hp, which would be close to an M5, if BMW didn’t thoroughly sandbag its factory horsepower numbers (an M5 is really more like 600 hp).