Step 1 - Make It Rigid:

… not that the stock M5 is a flexy-flier by any means, but you can always improve rigidity by adding front & rear strut tower braces:

The stock M5 handles extremely well… for a 4000lb sedan.  However it understeers moderately, especially at low speeds, and both front tires bear the brunt of any heavy cornering.  The Dinan stage 3 suspension setup replaces springs, sway bars, adds camber plates for more negative camber in front, and replaces the stock shocks & struts with adjustable Konis on all four corners.   The change lowers the car about ½”, which is barely noticeable (see picture).  However, the vehicle’s handling is transformed – it is as if 400 lbs had been removed from the vehicle.  It now turns in instantly with near-zero body lean, and holds a tight line even in slow corners.  All this, yet the ride quality is almost indistinguishable from the stock vehicle’s; unless you’re actively looking for clues, this could be a stock car… at least until you turn the wheel.  Dinan’s magic with suspension seems to be the ability to make any BMW handle like an all-out sports car while still riding like a luxury vehicle.  They’ve done it again with this package.

The stock M5 is a very fast sedan – it leaves the factory with 330 rear-wheel horsepower, will accelerate from 0-60 in 4.7 seconds and will cover the ¼ mile in 13.1s @ 108mph.  However, your humble editor is a somewhat jaded horsepower junkie; my previous car did the quarter mile in 11.0 @ 131.  The M5 isn’t likely to threaten those figures, but by opening up the intake and exhaust and adding a bit of pressurized breathing, the M5’s 5.0 liter V8 should be able to make close to 500 rear-wheel HP.  Stay tuned for further developments…

Step 3a - The Exhaust:

As a rule, stock exhaust systems are fairly restrictive.  In the case of the M5, the exhaust system in isolation is not a major bottleneck.  However, swapping the stock cans for a pair of Dinan stainless units added 7 HP, dropped 30 lbs (!), and added a pleasing, Corvette-baiting exhaust note to an otherwise sleeper car:

With the exhaust and ECU mods, the M5 doesn't pick up any peak horsepower on the dyno, but horsepower and torque improve 3% throughout the low-to-mid RPMs.  The chart below has my M5 in blue and a bone stock M5 in red.  Note the power increase everywhere except the top end:

 

Step 3b - The Intake:

Swapping the stock airboxes, hoses & resonators for a pair of beautiful carbon-fiber Dinan cold-air intakes with K&N filters allows the engine to breath a bit more easily.  Pictures and dyno figures to come shortly...