It may only be a 44hp boost over stock, but the extra 65 lb-ft of torque is a full 20 percent up. More aggressive ignition timing running closer to the knock sensor is possible thanks to the 100-octane Shell V-Power fuel. All this translates into an engine that can trickle around in town at 1200 rpm in third gear, yet comes alive like a thing possessed when you fully open the taps on the autobahn.
And it is when you give the engine its head that the grumbling, squirming chassis also changes its tune. Like a thoroughbred freed from a tiny paddock, the whole car wakes up and its highly focused purpose in life becomes abundantly clear.
Unlike the dampers in a luxury sedan, which are designed to have as little friction as possible for an ultra smooth ride, the dampers in a racecar need a certain amount of input to work properly. So while the secondary ride of the 135i CS in this track form is pretty jiggly at low speeds, when you start driving hard enough to load the suspension it all starts to come together.
On public roads, it's hard to get a true feeling for this car as I simply cannot use its full speed potential either in a straight line or around bends. But it's evident from the response at the helm, the pointy turn-in and the fabulous levels of mechanical grip that this car would be very quick indeed on the track.
BMW has not been noted for equipping even its M-cars with very convincing brakes. The Brembo brakes on the 135i are a step forward, but are given harder pads for duty in the Hartge car.
Knowing that Hartge always manages to achieve a near perfect balance between ride comfort and handling, I'd liked to try it on a track in this form, and then on the road with 19-inch footwear and the suspension settings backed off. That adventure, it seems, will have to wait for another day.
Hartge 135i Club Sport
Longitudinal front engine, rear-wheel drive
3.0-liter inline six, dohc, 24-valve, turbocharged and intercooled.
Hartge software, exhaust
Hartge coilovers, stabilizers
•Wheels and Tires
Hartge Classic 2, 9x20
Michelin Pilot Sport Cup, 245/30
Hartge chin spoiler, side skirts, trunk lid, rear valance, roof spoiler
Hartge steering wheel, handbrake, pedals
Peak Power: 350 hp @ 5660 rpm
Peak Torque: 354 lb-ft @ 2950 rpm
0-62 mph: 4.8 sec.
Top Speed: 174 mph