Tuner Tuesday Double Take: 2002 and 2003 BMW M5 Dinan S2s

There are a few select automotive tuners who can take an impressive package and refine it into an even better entity. That group includes legends such as AMG, Alpina and Ruf – all of which are staples of this segment.

Yet they are far from alone. Given the task of improving on what is generally considered to be one of the greatest sedans ever made is no small feat, but if there was one group up to it, it was Steve Dinan’s eponymous company in California.

While just about anyone can take a turbocharged engine and crank up the boost, slap a few stickers on it and call it done, the E39 M5 didn’t come with forced induction. On top of that, it was a motor which wasn’t exactly underdeveloped before it went into production. Nor were the brakes, suspension, or any other aspect of the third gen M5. But Dinan thought they could improve upon them, and with a tremendous amount of work, did.

Dinan went to town on the S62 from start to end. Out came the factory air boxes, air meters and velocity stacks, replaced by Dinan units of larger diameter and better flow qualities, along with larger throttle bodies bored out by the company. This necessitated reprogramming of the computer controls for the engine to match the new flow characteristics. To help the exhaust side of the motor, unique tubular headers were fit to a free-flowing, lightweight exhaust system. While this sounds a bit like old-school engineering, it was successful; the result was an additional 76 horsepower and 51 lb.ft of torque – basically, this was like adding a 1980 Rabbit’s worth of power to an already powerful car.

Dinan coupled the engine mods with a shorter final drive and higher rev-limiter to reach fantastic speeds. The S2 was capable of 0-60 runs around 4 seconds flat and, in unrestricted mode, geared out around 190 mph in 6th.…