According to Road & Track, Nissan is considering up to three different powertrain options for its next-generation Z. The powerplants run the gamut in terms of technology, but all put a greater focus on overall economy than the current car.
Another possibility - which has already been reported on these pages - is the use of a Mercedes-Benz' 3.0L turbo diesel. Under the hood of the of the E350 BlueTEC that mill makes 210 horsepower and 400 lb-ft of torque, but it's possible Nissan could bump up that horsepower rating to give the Z a more sporting feel.
Interestingly, Road & Track reports that Nissan could even offer the next Z with hybrid, diesel and gas engine options, giving buyers the ultimate in flexibility. Of course that scenario sounds a little farfetched to us, but we'll just have to wait until 2013 to see.
References
1.'Nissan Z - 2013...' view