I picked up my '09 coupe after having the Dinan 4.10 FD installed, along with the Dinan throttle bodies and Active Autowerke Signature Exhaust, by Co's BMW in Loveland, CO. I added my comments about the AA to the long-active thread about the AA. I can't say much about the throttle bodies yet because I'm delaying dyno testing until I get a few miles on the FD.
There are no surprises about the 4.10 so far, with engine speeds running 6.5% faster than before. As already noted in another thread, the speedometer runs off a wheel speed, so the FD has no impact on the speedo, which runs about 8 to 9% optimistic in my car. I will probably autocross on 30-series 18" tires, to gain another 5+% of gearing.
There's 6.5% more torque delivered to the rear wheels and it's easy to feel, but also part of the other mods that I made at the same time. I'm VERY pleased to report that there's no detectable gear whine added. I hear a little bit of gear noise when coasting down, but it's very minor. At 76 mph, including the impact of the AA exhaust, cruising noise level only moves from 73 dB to 74dB and I can't really attribute any of that to the FD. (I use a Radio Shack SPL meter to get my readings and did the before and after on the same piece of road, to try to eliminate road noise from the equation).
The potential noise is was worrisome to me because I couldn't get a reliable report here, or anywhere else that I tried. The guys selling the other gears whispered that the Dinan was noisy and whiney, but that's not the case, IME. Thank goodness. Shame on the guys putting out the bad vibe about the Dinan gears.
Unfortunately, I need to run-in the gears for 1200 miles and do a fluid change at that time before I can do some dyno runs to document where I am. Right now I'm getting down to the bottom of a tank of 100 octane unleaded race gas, and with all the mods my butt dyno is telling me that I'm North of 30 hp gained, net. It might be more, but my butt has been wrong before, so I'll hold the line there for now. When the gears are ready I'll put in another tank of 100 or 105, run it in for a day or two and then go to the dyno for detail reports. (We only get 91 octane at the pump here in CO, so I'm electing to test in race trim).
All these mods together had no negative impact on the cruising enjoyment of the car and added substantially to the overall kick when you put your foot in it.
Dave