Specialty File
Here's a shocker: We don't know a single automotive tuner who spends his leisure time under a shady tree reading William Shakespeare. So it's a good bet that tuner Steve Dinan will be reading the following warning from King Lear for the first time: "Striving to better, oft we mar what's well."
Not a problem, apparently, because with Dinan's latest work of art, he has not only fixed a car that wasn't broken but also sought to perfect a car that everyone considers to be as close to perfection as is humanly possible: the BMW M5. Then he casually sent the result to us for review. He didn't even chaperone the thing - he simply dropped it off and told us to keep it as long as we needed.
Conversation around the Lake Erie Spring Water cooler here at Hogback Road was skeptical. Dinan told us that his S2-M5 package - it costs $35,848 - upped the M5's horsepower from 394 to 470 and torque from 368 to 419 pound-feet, and did so without resorting to a turbo or supercharger. A 76-hp gain on a naturally aspirated engine would be an impressive feat on an unstressed, undeveloped engine, but the M5's mill is anything but unstressed.
The M5 V-8 is one of the most impressive motors ever built for the street. It is packed with four cams with infinitely variable valve timing, 32 valves, an aluminum block, eight electronically controlled throttle bodies - one for each cylinder - and an 11.0:1 compression ratio, and it's assembled with a care that results in 394 horsepower from 4.9 liters. It freely revs to 7000 rpm and never feels flat-footed, no matter how low the rev counter.
BMW coupled the engine to a six-speed manual transmission and a buttoned-down, lively chassis. We've never met an M5 we didn't love. It's won every comparison test it's been entered in, and if its $73,624 base price could be trimmed to get below our mid-$60,000 threshold for the 10Best Cars competition, it'd be a shoe-in for an award.
So we figured anyone trying to outdo BMW's engineers would, well, screw up. Maybe the result would be faster, but the M5's overall package could well be spoiled in the quest for more speed.
Dinan approached the task differently when he started on the M5 project two years ago. First, he set out to increase the engine's breathing characteristics. He ditched the stock airboxes and airflow meters for larger, better-flowing units and installed shorter, larger-diameter velocity stacks. Next he bored out each of the throttle bodies.
On the exhaust side, he installed a set of Dinan-made headers that resemble a pile of cooked spaghetti but flow well enough to create another 28 horsepower. In addition, he added a new exhaust system that sounds slightly raspier and weighs 29 pounds less than the stock system. Finally, Dinan lightened the flywheel by seven pounds.
These hardware changes are only a small part of the engine modifications. The real challenge was to reprogram the engine computer to take full advantage of the improved breathing. The M5's computer controls a myriad of engine functions, including the throttles, the timing of all four camshafts, and the usual bits such as the pulse-width and timing of the fuel injection. Each of these functions relies on the other, so change one - timing, for example - and then you likely also have to change everything else.
Writing the optimal program was a long, arduous, and iterative process that Dinan says took the bulk of the two years his company spent developing this package. But hard work paid off with the added 76 horses at peak power and a fatter torque curve that offers more torque at every rpm.
Coupled to the more powerful engine is a shorter final drive (3.45:1 versus 2.81:1). There are also slightly stiffer springs and shocks, special forged aluminum wheels, wider tires, and cooling ducts that direct air to the stock front brakes.
We found the benefits of these changes after our first run on the test track. Dinan's car is a rocket. It rips to 60 mph in 4.1 seconds, to 100 in 10 seconds flat, and through the quarter-mile in 12.7 seconds at 113 mph. The last M5 we tested needed 4.7 seconds to reach 60 mph and turned the quarter in 13.2 seconds at 109 mph. The S2-M5's top-gear acceleration from 50 to 70 mph improved 0.2 second, to 6.2. Dinan says that in addition to raising the stock 7000-rpm rev limit to 7300 rpm, he also removed the 156-mph top-speed governor. We didn't test for top speed, but Dinan suggests the S2-M5 can reach redline in sixth gear, which would be a hair-raising 191 mph. Skidpad grip climbed from the stocker's 0.83 g figure to 0.87.
And we did not find a downside, or any quirky behavior, with the increased performance. The exhaust system delightfully burbles at idle and emits a satisfying rasp at full throttle, but it settles into a subdued hum when cruising. The engine's throttle response is big-block instant. Thanks to the wide gear spacing of the M5's transmission, the shorter final drive does not make for frenzied highway cruising. At 80 mph in sixth gear, the engine revs at about 3000 rpm. Similarly, the suspension changes didn't ruin the M5's balance. Although we didn't have a stock M5 around for direct comparison, Dinan's S2-M5 had the same impressive combination of resilient ride and well-controlled body motions, but with even more grip.
It's a thoughtfully engineered package that feels as though it could have come from the factory. There are even side benefits we didn't expect, such as easier clutch engagement. We never realized how tricky it is to get a stock M5 rolling smoothly until we got in the Dinan car. Dinan says the lightened flywheel gets the credit.
Should you too have to fear of Shakespeare's warning, you may have the S2-M5 system installed on your M5 at any one of the 100 Dinan-licensed BMW dealers. Dinan will match the remainder of BMW's four-year/50,000-mile warranty and will also match that warranty if the package is installed on a new car.
Dinan also offers systems for the BMW 540i that include a supercharger. We haven't had a chance to try out that one yet, but for sure we won't be second-guessing it.
Dinan, 865 Jarvis Drive, Morgan Hill, California 95037; 408- 779-8584; www.dinanbmw.com.
