Since the M4's debut in late 2014, BMW has found ways to hone and improve upon its somewhat lackluster formula. There's the Competition Package, the hardcore GTS model, and the forthcoming CS, a configuration that's said to be something of a split between the two. But Dinan, the preeminent tuner of all things BMW, wasted little time setting to work on the M4. Within a year of the factory model hitting the street, Dinan had its M4 S1 ready for enthusiasts seeking something more potent. It offered a boost in power, refined handling, and visual flare to go along with a measure of exclusivity—and we were impressed. That was nearly two years ago, though, and those subsequently released factory packages have upped the ante to some degree.
Now 38 years on, Dinan has become synonymous with serious BMW tuning. It offers aftermarket upgrades with a similar level of quality and attention to detail as the factory equipment, while injecting even more performance and distinction to the equation. The outfit also serves as a technical partner to BMW Motorsport in the Rolex Grand-Am Daytona Prototype series. It's continued to prove its worth by contributing to the team's back-to-back championships and two overall wins at the 24 Hours of Daytona, successes that bode well for the company's ability to design and manufacture high-performance upgrades for its road cars.
While it's not a reinvention of the company's tuning strategy for the high-performance coupe, this latest iteration of Dinan's ultimate M4 package—the S2—promises to improve upon it in enough meaningful ways to justify a new badge. But the proof is in the pudding, of course, so we headed out to the winding stretches of tarmac in the Angeles National Forest just northeast of Los Angeles to find out for ourselves.
"As with all our vehicles, the idea behind the M4 S2 is a holistic approach that offers a complete package," says Dinan's Dan McNiff. "Our intention is to provide the best possible iteration of the vehicle in both power as well as handling." While it might be easy to dismiss that as marketing speak, the upgrades applied to the M4 S2 touch upon nearly every aspect of its performance, yielding a car with a decidedly more hard-edged character than when it left the factory and objectively more capable as a result.
Nowhere is that difference made more obvious than in the M4 S2's suspension tweaks. As with the S1, the M4 S2 incorporates Dinan's coilover kit, which retains the factory dampers whether they're adjustable or fixed. Dinan describes the kit as being honed from its motorsport efforts but dialed in for street use with the intention of reducing brake dive, body roll, and squat under acceleration while offering reasonable ride quality during everyday use, provided owners opt to keep the ride height within the recommended specifications—most people will ignore that last part, resulting in a car that handles worse.
Those coilovers are supplemented by Dinan's tension strut ball joint kit, which is designed to reduce the deflection that's inherent to the factory rubber bushings in the thrust arms by replacing them with machined aluminum housings and new ball joints, as well as its sway bar set and rear suspension link kit, the latter of which differentiates the S2's suspension tuning from the M4 S1.
Designed to address the stock M4's susceptibility to rear steer, the rear suspension link kit replaces the toe links' curved alloy rod and rubber bushings with a straight billet aluminum rod and Teflon-coated machined steel rod ends to reduce the suspension's tendency for excessive toe change under hard acceleration and braking. The front trailing links are given a similar treatment to address the factory setup's tendency to flex under load.
Combined with camber plates that allow for up to 2.5 degrees of negative camber and just over a degree of positive camber adjustability, Dinan's suspension tuning efforts are undeniably comprehensive. But in an effort to maintain a semblance of the factory car's balance among the various aspects of its performance, the M4 S2 also features a number of tweaks under the hood.
Like the S1, the M4 S2 benefits from a more aggressive-sounding low-restriction exhaust system that's coupled with a high-flow cross-pipe. On the other side, a carbon-fiber cold-air intake gives the engine bay some additional eye candy while providing more air at cooler temperatures through its less restrictive design. The S2's setup improves on that of the S1 by the use of its Stage 3 tuning system, designed to not only take advantage of the new intake and exhaust components but the S2's new heat exchanger as well, which addresses the limitations of the stock cooling system with 60 percent more volume and 19 percent more surface area than its factory counterpart. Dinan says the new heat exchanger allows the charge air to be cooled by an additional 6-degree average across the rpm range compared to the stock unit, and it contributes to the M4 S2's peak output figures of 548 hp and 549 lb-ft of torque, gains of 123 hp and 143 lb-ft over a stock M4, and 18 hp/45 lb-ft over that of Dinan's M4 S1. "The stock cooling system heat soaks after only three pulls and allows the engine air intake temperatures to rise significantly," McNiff explains. "The ECU must then reduce engine power to prevent detonation. With the Dinan heat exchanger, the vehicle will not heat soak, even after seven pulls."
It doesn't take more than a few seconds of driving the M4 S2 to realize that this is a significantly different beast than the factory M4. With this tester's fixed dampers, the S2's ride is admittedly firm around town, though well within the acceptable range for most performance-focused drivers. Those willing to tolerate the more significant impacts over low-speed bumps will be rewarded once they get out to a good stretch of road with a suspension that feels far more connected and steering that feels much more precise and quicker to respond.
Combined with the copious grip offered by Dinan's optional wheel and tire package, which uses Pirelli Pzero Corsa rubber on forged alloys measuring 20x9.5 inches up front and 20x10.5 inches in the rear, the M4 S2 simply feels more composed and inspires more confidence at speed. The suspension tweaks help ease some of the shortcomings of the M4's steering, too, providing more immediate turn-in and significantly reduced body motion without entering into the realm of mid-corner nervousness that can result from overly stiff suspension tuning. Simply put, this M4 feels more at home on twisty mountains roads than any modern BMW I've driven, and that includes the Dinan M2 S2.
The powertrain upgrades seem to yield less obvious benefits, though. The tone of the exhaust remains subtle when cruising and totally free of cabin drone throughout the rev range but can be harsh and dissonant at wide-open throttle with sudden swings in volume. There's also some sense that those substantial horsepower and torque gains over stock should be more noticeable, but what ultimately seems to be made most obvious is the turbo lag below 4k. However, where many turbocharged setups give nearly everything they have to offer in the midrange, the M4 S2 actually feels at its strongest toward the top end, encouraging you to wring out each gear to get the last bit of performance out of that inline-six.
Dinan considers the M4 S2 a complete package of modifications designed to work in harmony with one another. The marketing guys are quick to point out that all of these upgrades are available individually, allowing owners to do these upgrades incrementally or forego certain aspects of the S2 package entirely, if they so choose.
For those looking to knock it all out in one fell swoop, the S2 package rings up to $13,282 before installation. That includes the engine and suspension upgrades along with Dinan's aluminum pedal set, serialized plaque, and requisite branded badging. The optional wheel package will add another $6,550 to the mix, while carbon-fiber mirror caps, a front splitter, and spoiler from BMW will cost you another $2,205.
Although that's not an insignificant amount of coin to add to the bottom line, the fact that these upgrades can be done a la carte makes them significantly more accessible, and Dinan's warranty of up to four years and 50,000 miles speaks volumes for the company's confidence in its products. While there might be less expensive ways to coax performance out of a stock M4, a heavily tuned car that doesn't behave like one is a virtue in and of itself.