I've never warmed up to the new BMW M5. Yes, it's got gobs of torque and toys galore, but it still feels like a warmed-over 550 – a bit of a punt on a marque that deserves more. Steve Dinan tends to agree. Not just because his business depends on it, but because he's obsessed – and I don't use that word lightly – with making a better BMW. And oh yes, this is much, much better.

Dinan really isn't a "tuning" company anymore. It's a software firm that also engineers and manufacturers beautiful bits of go-fast artwork. But the real highlight of the company's S1 M5 isn't the new exhaust or the painfully perfect pair of carbon fiber cold air intakes, but the custom computer Dinan created to run it all.

A little over a year ago, one of Dinan's software engineers walked into Steve's office and dropped a bombshell. It's impossible – "it" being cracking BMW's encryption on the F10 chassis. That's the first time in Dinan's history that it hasn't been able to gets its mitts into BMW's code and bend it to their will.

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After trying every conceivable solution, Steve and Co. finally pulled the trigger on what's now known as Dinantronics, a completely custom, plug-and-play ECU that gives the company the control it needs.

This is not easy.

Hop on eBay or any BMW forum and you'll see dozens of cheap hacks that raise boost pressure on the twin-turbo 4.4-liter V8 (S63B44Tü for you code nerds). The problem is when the boost is raised, the factory computer freaks out, tripping over itself to correct the fuel mixture, ignition timing, and a host of other parameters. Eventually the angry engine starts throwing codes. At best power is lost. At worst, the $299 black box from BestBMWTUNRES just voided your warranty and broke some very expensive things.

The Dinantronics setup takes in all the information and tweaks it accordingly, from air/fuel mixtures to ignition timing in a blur of gee whiz tuning that I can only assume requires a wizard hat and a sacrificial chicken. And it does all of that while keeping the trim corrections – that is both the ideal and scheduled fuel mixture – within the specifications of BMW's propellerheads. It also makes power.

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With the carbon fiber intakes joining the freer-flowing exhaust, the S1 M5 gets boosted by 115 horsepower – from 560 to 675 hp – and torque goes up by 144 lb-ft to 644 pounds of twist. And oh-my-god-yes, this is the way it should've come out of Munich.

While the standard M5 – even with the Competition Pack – was no slouch off the line, things get more interesting much more quickly in the Dinan machine. From a standstill there's no doubt that the S1 M5 is easily in the high 3-second range when running to 60 MPH, and it's pure torquetastic bliss until 1,500 RPM shy of the 7,200 RPM redline. The seven-speed dual-clutch transmission doesn't just cope with the extra power, but revels in, snapping off eerily composed shifts with vigor. And yes, Dinan makes this kit for the manual, too. (And its M6 cousins.)

But I expected power. That's a given with Dinan. What I wasn't expecting – and what had me cackling through arms of opposite lock – was the suspension upgrades.

Part of every new Dinan's testing regime includes a months-long stint as Steve's daily driver, and the suspension was where he found the biggest faults. That lumbering, confidence-sapping sensation – exacerbated by the electric steering, mind – has been all but eliminated. The pair of adjustable tubular sway bars (28mm front and 22mm rear) are part of the recipe, but the new coil-overs coupled with the Michelin Pilot Super Sports (285/30 front, 305/30 rear) make magic.

Dinan managed to retain the Electronic Damper Control shocks, but wrapped them in adjustable springs that drop the M5 by 1.25 inches and then fitted progressive bump stops to round things out. The result is remarkable direct turn-in and nearly nonexistent body roll that feels more connected and controlled than anything weighing over two tons. What's more, Dinan has done all of that without making the ride perceptively more punishing. It's hardly a hunkered-down sports car, but for anyone buying the M5 as a performance weapon – and not just for the badge – it's an absolute must have, and it's also the least expensive thing on offer at $2,497.

Yes, cost is always the issue with Dinan's wares, sparking forum flame wars by armchair knee-jerks, and the engine upgrades are no exception. The full S1 package – the exhaust, the intakes, and the custom ECU – rings up at $9,747 and carries Dinan's 4-year/50k-mile warranty. As impressed as I was with the power, that's still a tough sell. Then again, I also don't have $100k to drop on a sports sedan. But if you're serious about speed and adore four doors, Dinan's reworked M5 is the answer. It's a point-to-point projectile that manages to blend fury and control into one of the most compelling, over-endowed sedans I've driven in ages. And it feels like it could've rolled right off of BMW's assembly line, because it should have.

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