New Car Reviews

First Drive: 2018 Dinan S1 BMW M550i xDrive

Keeping up with the Joneses

Boy, we’ve sure got it good. From the top to the bottom of the market, outright speed is increasingly egalitarian in this horsepower-swollen golden age. Somehow, in the relatively short timeline between shaking off the OPEC crisis and trying to solve the bigger secrets of Martian occupation, we’ve found ourselves with the impossible task of picking between a seemingly endless line of sedans packing over 450 hp. Up the ante and there are still enough options at the 600-hp-plus tier that it would require trips to seven different dealerships to test them all.

It’s even freakier if you’re willing to fiddle with your new super-bruiser. Established companies like Dinan will cheerfully turn an already capable car into fire-spitting lunatic. The sesquipedalian 2018 Dinan S1 BMW M550i xDrive is a prime example of this private sector arms race, sporting enough under-hood dynamite to match the all-new 2018 BMW M5.

You guessed it, the core of the car in question is formed around the M550i xDrive, a current member of our Four Seasons fleet. Even without the Dinan regimen, it’s a burly car—the 4.4-liter twin-turbo V-8 spins out a meaty 456 hp and 480 lb-ft of torque, enough to send the 4,372-pound brawler to 60 mph in under four seconds.

From the factory, the M550i carries a weighty $74,445 price tag, so don’t expect this to play out as “cheap speed,” though what comes next isn’t much in comparison to the initial buy-in. My dark blue tester wore Dinan’s ECU tune, an upgraded quad-exhaust, and an upgraded midpipe , the combination of which twisted another 150 hp and 155 lb-ft of torque out of the engine, settling at an estimated 606 hp and 635 lb-ft of torque. Leave the rest of the order sheet blank and Dinan’s bill stops at $5,649.

In theory, a combined investment of $81,094 (to start) nets you a brand-new 5 Series that should keep up with the newly minted sixth-gen BMW M5, at least in a straight line. On paper, the figures are compelling–the M5 uses the same 4.4-liter twin-turbo V-8 as the M550i, but power is down compared to the Dinan, with the M5 putting out 600 hp and 553 lb-ft of torque.

Agitate the M5 and it cracks off 0-60 mph in a claimed 3.4 seconds, but instrumented tests see results drop just under the 3.0-second mark. There’s no official performance data from Dinan, but considering the regular M550i already breaks the four-second barrier, hustling the S1 feels every bit of a healthy low-three-second car.

Power hits low, and hard. Like other semi-massive Teutonic sleds of the same segment, the two-ton-plus mass mutes the sense of speed, until the landscape becomes unsettlingly blurred. It’s a seat-masher, for sure, but keep an eye on the speedo—it spins up faster than you might expect.

I explored the S1’s powerband best I could in the claustrophobic Malibu canyons, but this is a car better suited for the wide sweepers of Angeles Crest. Regardless, the Dinan squeezed through the Santa Monica Mountains with unexpected poise, thanks in part to the S1’s upgraded springs and “Ride Quality/Handling Kit.” Spring stiffness is improved by fifteen percent in the front and rear, and the overall ride height is cut by 0.75 inches. The aforementioned “Ride Quality/Handling Kit” adds “progressive rate” bump stops, mitigating any nasty bottoming-out that might come from the new springs. Ordering the whole caboodle costs a combined $448, which is mighty affordable considering the $80,000 buy-in.

The tester also rode on a set of handsome 20-inch Forgeline AR1 wheels, wrapped with Michelin Pilot Sport 4Ss–265 sectionals in the front, 295s in the back. They looks great, but if you’re trying to widen the price gap between the M5, leave these off the order form–they’ll set you back $6,550.

This is where the Dinan and the M5 begin to diverge. Even with the extra handling hardware, the Dinan is comprehensively outgunned by the M5’s mil-spec chassis upgrades. The F90 M5 arrives fresh from the factory bristling with tools honed at (and for) the harshest circuits around the world, so it’s no surprise the M5 is sharper, more explosive, and more clever than the Dinan when pushed.

The Dinan retains the M550i’s overboosted ez-turn steering, along with the same brakes and on-board chassis management systems that don’t stack up. Even with the spring and bumpstop concoction, it can’t scrub one hundred percent of the M550i’s cushy, lean-happy character.

This isn’t a condemnation of the Dinan–I mention this only to put both cars into the same context. The S1 is just as comfortable and easy to drive as the regular M550i, and if you leave off the fiendishly expensive wheels, it’s stealth speed. Even compared to the M5’s reasonably staid appearance, the S1 is one of those great trans-continental bullet trains that should come pre-equipped with a state-of-the-art radar detection system and pre-entry into any clandestine Cannonball Run-style rallies. Not that I condone any of that, natch.

You’re also saving $20,000 over the M5, and if you live outside one of the very few places with good driving roads, I’d say pocket the cash and stick with the Dinan. If you’ve already got an M550i kicking around in the garage, it’s high-time you gave them a call. After all, you’ve got to keep up with the times–456 hp just isn’t cutting it anymore.

2018 BMW Dinan S1 M550i xDrive Specifications

ON SALE Now
PRICE $81,094 (base w/power kit)/ $98,144 (as tested)
ENGINE 4.4.L DOHC 32-valve twin-turbocharged V-8/606 hp, 635 lb-ft
TRANSMISSION 8-speed automatic
LAYOUT 4-door, 5-passenger, front-engine, AWD sedan
EPA MILEAGE 19/25 (city/hwy)
L x W x H 195.4 x 73.5 x 57.8 in
WHEELBASE 117.1 in
WEIGHT 4,400 lb (base)
0-60 MPH 3.0 seconds (est)
TOP SPEED N/A

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