Found this on Truck Trend:
Why don't we get the 3.7? Infiniti cites a few reasons. The company wanted to differentiate the V-6 and V-8 models, and one element of that was by widening the performance gap.
There was only a 42-horsepower difference between 2008 FX35 and 45; the new engines are now separated by nearly 90 horses. Also, the 3.5-liter's 303 horses are only 27 fewer than the 3.7 puts out, and its 6.1-second 0-to-60 time is actually faster than the previous FX45's. Despite what Infiniti says, though, the real story may be one of cost: the 3.7-liter is a more complex engine, and using it could've driven up the MSRP on U.S. models.
http://www.trucktrend.com/features/n...x35/index.html