[swamp2]

Guys, there has been a lot of debate about differentials. In short a higer FD ratio does produce more wheel torque and more wheel power however, the trade off is less time accelerating in each gear (i.e. you have to go to 2nd which is much lower acceleration than 1st while the car with the stock diff is still pulling hard to a higher speed before the 1-2 shift, similarly across all gears). There has also been a lot of debate (mostly in the past) about physics based simulation for determining a vehicles performance. In short simulation is pretty well accepted and has been shown to be quite accurate across a large range of vehicles. I finally decided to run some sims of the M3 (M-DCT) with the stock FD (3.15) vs. a 3.45 and 3.62. This is actually one of the best cases to simulate since it essentially washes out any baseline effects, the only changes to each set up is the FD ratio and therefore even though you might see some inaccuracy on an individual run the RELATIVE results between these results and any apples to apples real world test should be excellent.

In short the 3.45 FD has little to no effect (except at very high speeds) but the 3.62 has a combination of positive effects with few downsides. #1 is stock, #2 is 3.45 and #3 is 3.62. I think this goes against much of the guesses and common wisdom on the topic. Personally, I trust simulation as much or even more than test. Tests often get obfuscated with many non controlled/controllable factors leading to a non apples to apples scenario.