I tracked my N55 135i for the first time this weekend, and it performed better than I expected. Having run prior track days in an Exige, the weight of the 135i is immediately apparent, but so is the comfort day-to-day. After this event, I'm convinced that this car can serve effectively as a dual-purpose vehicle.
BMW Performance Power Kit (PPK1)
BMW Performance Suspension
M3 Front Control Arm Kit (includes control arms, wish bones, sway bar, springs, struts)
M3 Rear Subframe Bushings
Forge Motorsport FMIC
Ferodo DS2500 Pads + 600*F brake fluid
100 octane gas
This was my best lap, even though I flubbed turn 11 (the last one). 1:50:99sec.
The power was sufficient, but the most impressive aspect of this vehicle on the track was the braking power. Absolutely zero fade, and tremendous stopping power. I'd say it stops better than the stock brakes on my Exige. Really, really strong braking capability. I don't know how much of this is attributable to the pads, the fluid, or the beefy stock caliper/disk setup, but I can say with confidence that this combination works well.
Since the event, I noticed that the brakes do make a LOT of noise on the street. I never did a full bedding procedure prior to track day, so that may help. Otherwise, I may throw the stockers back on till the next event.
I got the intercooler to discourage overheating. We had very mild ambient temps in the low 70's and high 60's, so it may not have been an issue anyway. But I'm happy to have the FMIC regardless. Before/after dyno runs showed a nice little bump in HP and area under the curve in torque from installing the Forge unit.
The suspension is as stiff as I'd want a daily driver to be. It's not too low for even the largest speed bumps, and not too jarring to take on long trips either. For me, it's the Goldilocks "just right" balance for street and track.
Happy to field any questions.