The plain old BMW 4-Series is already a pretty darn good performance coupe straight outta Munich. Its 2.0-liter four or 3.0-liter six each makes more than enough power to get out on the road and have fun: 248 hp for the four and 320 hp for the six. The stock 4-Series gets to 60 mph in 5.6 and 4.8 seconds, respectively. BMW itself says the 4-Series “…embodies the very essence of dynamics and aesthetic appeal in the premium segment.”

That’s just the entry-level 4. From there, you step up to the M4 Coupe. The M4 and its twin-turbo double-VANOS 3.0-liter six make 425 hp and launches to 60 mph in 3.9 seconds. BMW lists a Nurburgring lap time of 7:52 for the M4, which ain’t bad at all. BMW further points out that you can get an M4 with 444 hp if you get the Competition Package. The M4 has carbon-fiber reinforced plastic roof, trunk lid, engine brace and even driveshaft to lighten it up. The Active M differential further enhances performance underway.

But is that enough? Would you like more? Because Dinan offers more.

The Dinan S2 M4 makes a listed 548 hp and 549 lb ft of torque. Adjustable coilovers and a whole bunch of suspension bits make it a car for the track more than the street.

I just drove a Dinan F82 M4 S2, which offers a laundry list of power and performance perks. Let’s start with the power. The engine on my test car was upgraded with a “Dinantronics Performance Tuner Stage 3” kit, a carbon-fiber cold air intake, free-flow stainless exhaust, high-flow X-pipe and high-performance heat exchanger. Dinan lists power with this tune at 548 and torque at 549 lb-ft. That’s 123 hp over the stock M4. You can’t do that with intake and exhaust, no matter how good those components are. The key is that Dinantronics Performance Tuner Stage 3 thing. Dinan lists it as “…a highly engineered and sophisticated piece of computer hardware and software that enhances engine performance…” It's a so-called piggyback unit that sits on the BMW ECU.

"We’re working with all the same sensors, we’re doing all the same stuff, but it’s intercepting the signal as opposed to basically replacing the map from the factory ECU," said a Dinan spokesman.

I personally think it just clamps the wastegates down a little longer, but I‘m sure it’s more complex than that. In any case, wastegate-clamping could easily get you 548 peak horsepower, so I will believe it. And Dinan says this tune is legal in all 50 states, does not void the new-car warranty and does not affect long-term reliability. I only had it for a couple hours, but it was reliable that whole time.

The other Dinan parts on my M4 S2 are aimed at keeping the wheels on the ground. To that end, my test car got Dinan’s adjustable coil-over suspension system, sway bars, rear link kit, tension strut ball-joint kit and adjustable camber plates. Many a tuner will simply install lowering springs and be done, so it’s impressive that Dinan includes so many items here. My car also had 20-inch forged wheels and 275/30 front and 305/30 rear Pirelli P-Zero Corsa tires, plus some trim items.

The Dinan S2 M4 makes a listed 548 hp and 549 lb ft of torque. Adjustable coilovers and a whole bunch of suspension bits make it a car for the track more than the street.

So how does it drive? Well…

Sometimes too much is just too much, especially in the tuner world. When it comes to horsepower, too much is generally fine, but suspensions are another matter. They’re delicate things that require perfect balance matched to each particular track or canyon road to work at their best. Given that most roads -- and even racetracks -- are not pizza-spatula-smooth, a little compliance in the suspension tuning is often what you want. Let it soak up the bumps. The idea is to keep the contact patches on the ground as much as possible. Crank it down too tight and the contact patches, along with the rest of the car, go bouncing down the road.

Which brings us to the Dinan BMW S2 M4. With this car, using the setup I had for an afternoon, it felt like Dinan had just cranked the thing down to the stops and left me, the poor, hapless driver, to bounce down the road. This is fine with many enthusiasts, who will think, “I’ve really got a performance car here!” Well, I gotta think a little discretion in shock and spring tuning is in order.

The Dinan S2 M4 makes a listed 548 hp and 549 lb ft of torque. Adjustable coilovers and a whole bunch of suspension bits make it a car for the track more than the street.

My ride in the S2 M4 comes just a few short months after my rides in the Dinan M1 and S2 M2, and a couple years after my ride in an S3 M235i. In all those cars, the ride was too firm for normal street use but felt much better in enthusiastic canyon-carving. In the current test subject, the S2 M4, it felt too stiff even in the canyons. Generally speaking, on all of them, I would have softened up the springs to match the shocks and bushings to a real road. With this S2 M4, though, as with all the other Dinans I’ve driven in the last year, the hardcore Dinanites will say they love the maximum crankage they get with this kind of setup. But I’m here to tell you that if your tires aren’t on the ground, you’re not going to be cornering as fast.

Here’s why I came to this conclusion: Upon getting the keys, I took it immediately on some favorite roads way out on the west end of the Santa Monica Mountains. Maybe you know the roads. The setup was so firm that it felt almost bouncy. One stretch in particular, where a well-known road has curves so tight that it’s almost like an autocross course, I had to slow down considerably as the car hopped around, particularly under braking when entering corners. Too much braking combined with too much steering input and the rear wheels would jump over just a bit. Or at least it felt like that. Even though the M4 should have been a more compliant ride, given the slightly longer wheelbase versus the M2, this car felt the opposite. This was despite having tapped “M2” on the wheel setting to get what I was told was the optimum setting for carving these particular canyons.

Given the limited time I had with the car, I was unable to find a spot to try some 0-60 launches, which would have highlighted the power advantage offered in this tune. But as I said, I’m willing to accept Dinan’s claim of 548 hp.

The pricing for this setup, assuming you’re a real driving enthusiast and want something this stiff, is actually quite reasonable. The engine and suspension upgrades on my borrowed S2 M4 came to $13,282. Add $6,550 for a set of those lightweight forged wheels, $2,205 for the carbon-fiber spoiler and splitter, as well as the mirror caps, and you’d have the car you see here. It’s still well under the cost of the elusive and long-since-sold out M4 GTS, and it offers more horsepower and torque than the GTS. Plus, the Dinan name carries some prestige among the cognoscenti.

While it may not have been exactly the way I’d have set up an M4, it is the way many, many Dinan customers like theirs. And everybody knows those guys are fast.

Vehicle Model Information

ON SALE: Now

AS TESTED PRICE: $13,282 plus price of BMW M4

POWERTRAIN: 3.0-liter twin-turbo six, 7-speed DCT

OUTPUT: 548 hp, 549 lb-ft (mfg.)

OPTIONS: DINANTRONICS Performance Tuner Stage 3 $3,088, Dinan Stainless Steel Free Flow Exhaust (Black Tips) $2,574, Dinan High Flow X-Pipe $849, Dinan High Performance Heat Exchanger $699, Dinan Carbon Fiber Cold Air Intake $2,059

PROS: As stiff as you're likely to want it...or anything

CONS: Stiffer than I want it

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